llvm-native-core 0.1.16

//! X86 Code Emission Preparation — final code emission preparation pass
//! for X86/X86-64 targets. Handles constant island placement, jump table
//! emission, alignment padding, CFI/DWARF debug info, exception tables,
//! section switching, symbol emission, relocation emission, and object
//! file section organization.
//!
//! ## Emission Phases
//!
//! 1. **Constant Island Placement**: Place large immediate constants and
//!    constant pools within reachable distance of their references.
//!    Supports both data-in-code (literal pools after unconditional
//!    branches) and separate constant sections. Handles PC-relative
//!    addressing limits (±2 GB for x86-64 direct, ±2 KB for x86-32).
//!
//! 2. **Jump Table Emission**: Emit jump tables for switch statements.
//!    Supports all forms: direct jump tables (JMP [table + index*8]),
//!    indirect jump tables, and PC-relative jump tables. Handles table
//!    alignment, entry size, and range-checked access.
//!
//! 3. **Alignment Padding Emission**: Emit NOP padding for function,
//!    basic block, and loop alignment. Multi-byte NOP sequences optimized
//!    for each microarchitecture (Intel recommended NOP lengths, AMD
//!    NOP fusion optimization). Hot/cold code separation alignment.
//!
//! 4. **CFI Instruction Emission**: Emit Call Frame Information (CFI)
//!    directives for DWARF .eh_frame / .debug_frame. Covers CFA
//!    (Canonical Frame Address) setup, register rule changes, remember/
//!    restore state, and window save/restore operations.
//!
//! 5. **Debug Line Emission**: Emit DWARF .debug_line section with
//!    line number program. Supports standard opcodes, extended opcodes,
//!    special opcodes, and file/directory tables. Includes prologue
//!    length calculation and optimized line table encoding.
//!
//! 6. **Exception Table Emission**: Emit LSDA (Language-Specific Data
//!    Area) for exception handling. Covers GCC except table format
//!    (LPStart, TType, call site table, action table), and Windows
//!    exception handling (UNWIND_INFO, RUNTIME_FUNCTION, handler data).
//!
//! 7. **Function Boundary Alignment**: Emit NOP padding to align
//!    function entry points to specified boundaries (16-byte default,
//!    configurable). Handle hot/cold function splitting alignment.
//!    Support Intel CET endbr64/endbr32 landing pad alignment.
//!
//! 8. **Section Switching Emission**: Emit section directives to switch
//!    between code (.text), data (.data, .rodata), BSS (.bss), and
//!    custom sections. Track current section state to avoid redundant
//!    switches. Support ELF section flags, types, and entsize.
//!
//! 9. **Data Fragment Emission**: Emit initialized data fragments:
//!    .byte/.word/.long/.quad/.octa, .ascii/.asciz/.string, .zero/.space,
//!    .fill, and composite data (struct/array initializers). Support
//!    leb128 encoding for DWARF sections.
//!
//! 10. **Symbol Emission**: Emit symbol definitions and references:
//!     global/local symbols, weak symbols, common symbols, absolute
//!     symbols. Support symbol attributes: visibility, binding, type,
//!     size. Emit symbol table entries and string table.
//!
//! 11. **Relocation Emission**: Emit relocation entries for unresolved
//!     references. Support all X86 relocation types (R_X86_64_*,
//!     R_386_*). Handle PC-relative, absolute, GOT, PLT, TLSDESC,
//!     and GOTPCREL relocations. Compute addends and apply fixups.
//!
//! 12. **Object File Section Organization**: Organize sections into
//!     the final object file layout. Determine section ordering,
//!     segment mapping for ELF, section alignment, file offset
//!     assignment, and index assignment. Handle mergeable sections
//!     (string merging) and section groups (COMDAT).
//!
//! ## Microarchitecture-Specific NOP Sequences
//!
//! | Length | Intel Recommended          | AMD Recommended        |
//! |--------|----------------------------|------------------------|
//! | 1      | 90 (NOP)                   | 90 (NOP)               |
//! | 2      | 66 90 (NOP DWORD)          | 66 90                  |
//! | 3      | 0F 1F 00 (3-byte NOP)      | 0F 1F 00               |
//! | 4      | 0F 1F 40 00 (4-byte NOP)   | 0F 1F 40 00            |
//! | 5      | 0F 1F 44 00 00 (5-byte)    | 66 66 90 66 90 (alt)   |
//! | 6      | 66 0F 1F 44 00 00 (6-byte) | 0F 1F 80 00 00 00 00   |
//! | 7      | 0F 1F 80 00 00 00 00      | 0F 1F 84 00 00 00...   |
//! | 8-15   | Multi-byte NOP patterns    | Multi-byte patterns    |
//!
//! Clean-room reconstruction from:
//! - Intel® 64 and IA-32 Architectures Software Developer's Manual
//!   (Volume 2B, NOP instruction; Volume 1, Chapter 7: Programming
//!   with General-Purpose Instructions)
//! - DWARF Debugging Information Format, Version 5 (Sections 6.2:
//!   Line Number Information, 6.4: Call Frame Information)
//! - System V Application Binary Interface: AMD64 Architecture Processor
//!   Supplement (Section 4: Object Files, Relocation Types)
//! - ELF Specification (TIS Committee), Section 3: Object Files,
//!   Section 4: Relocation
//! - Microsoft x64 Software Conventions (Exception Handling, UNWIND_INFO)
//! - GCC Exception Handling ABI (LSDA encoding, personality routines)
//! - Agner Fog's Microarchitecture Manuals (NOP sequences, alignment)
//!
//! Zero LLVM source code consultation.

#![allow(non_upper_case_globals, dead_code)]

use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet, VecDeque};
use std::fmt;
use std::mem;

use crate::codegen::{
    MachineBasicBlock, MachineFunction, MachineInstr, MachineOperand, PhysReg, VirtReg,
};
use crate::x86::x86_instr_info::{X86InstrInfo, X86Opcode};
use crate::x86::x86_register_info::{RAX, RBP, RBX, RCX, RDI, RDX, RFLAGS, RIP, RSI, RSP};

// ============================================================================
// Constants
// ============================================================================

/// Default function alignment boundary.
pub const DEFAULT_FUNCTION_ALIGNMENT: u32 = 16;

/// Default basic block alignment for hot blocks.
pub const DEFAULT_BLOCK_ALIGNMENT: u32 = 4;

/// Default loop alignment for performance.
pub const DEFAULT_LOOP_ALIGNMENT: u32 = 16;

/// Maximum PC-relative jump displacement for x86-64.
pub const MAX_PC_REL_DISP_64: i64 = 0x8000_0000; // ±2 GB

/// Maximum PC-relative jump displacement for x86-32.
pub const MAX_PC_REL_DISP_32: i64 = 0x8000_0000;

/// Maximum short jump displacement (8-bit signed).
pub const MAX_SHORT_JUMP: i64 = 127;
pub const MIN_SHORT_JUMP: i64 = -128;

/// Maximum near jump displacement (32-bit signed).
pub const MAX_NEAR_JUMP: i64 = 0x7FFF_FFFF;
pub const MIN_NEAR_JUMP: i64 = -0x8000_0000;

/// Maximum constant island reach (for x86-64 RIP-relative addressing).
pub const MAX_CONSTANT_ISLAND_REACH: i64 = 0x7FFF_FFFF;

/// Default constant island alignment.
pub const CONSTANT_ISLAND_ALIGNMENT: u32 = 8;

/// Maximum number of entries in a single jump table.
pub const MAX_JUMP_TABLE_ENTRIES: usize = 4096;

/// Default jump table entry size in bytes.
pub const JUMP_TABLE_ENTRY_SIZE_64: u32 = 8;
pub const JUMP_TABLE_ENTRY_SIZE_32: u32 = 4;

// Multi-byte NOP sequences
pub const NOP1: &[u8] = &[0x90];
pub const NOP2_INTEL: &[u8] = &[0x66, 0x90];
pub const NOP3_INTEL: &[u8] = &[0x0F, 0x1F, 0x00];
pub const NOP4_INTEL: &[u8] = &[0x0F, 0x1F, 0x40, 0x00];
pub const NOP5_INTEL: &[u8] = &[0x0F, 0x1F, 0x44, 0x00, 0x00];
pub const NOP6_INTEL: &[u8] = &[0x66, 0x0F, 0x1F, 0x44, 0x00, 0x00];
pub const NOP7_INTEL: &[u8] = &[0x0F, 0x1F, 0x80, 0x00, 0x00, 0x00, 0x00];
pub const NOP8_INTEL: &[u8] = &[0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00];
pub const NOP9_INTEL: &[u8] = &[0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00];
pub const NOP10_INTEL: &[u8] = &[0x66, 0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00];
pub const NOP11_INTEL: &[u8] = &[
    0x66, 0x66, 0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00,
];
pub const NOP12_INTEL: &[u8] = &[
    0x66, 0x66, 0x66, 0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00,
];
pub const NOP13_INTEL: &[u8] = &[
    0x66, 0x66, 0x66, 0x66, 0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00,
];
pub const NOP14_INTEL: &[u8] = &[
    0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00,
];
pub const NOP15_INTEL: &[u8] = &[
    0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00,
];

// ============================================================================
// Enums and Supporting Types
// ============================================================================

/// NOP sequence optimization preference.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum NOPVariant {
    /// Intel recommended multi-byte NOPs.
    Intel,
    /// AMD recommended multi-byte NOPs (some differences).
    Amd,
    /// One-byte NOPs only (size optimization).
    SingleByte,
    /// Long NOP (0x66 0x66 ... 0x90) for specific uarchs.
    LongNop,
}

/// Section type for ELF object file.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ElfSectionType {
    /// Not present in the file (SHT_NULL).
    Null,
    /// Program data (SHT_PROGBITS).
    Progbits,
    /// Symbol table (SHT_SYMTAB).
    Symtab,
    /// String table (SHT_STRTAB).
    Strtab,
    /// Relocations with addends (SHT_RELA).
    Rela,
    /// Symbol hash table (SHT_HASH).
    Hash,
    /// Dynamic linking information (SHT_DYNAMIC).
    Dynamic,
    /// Note section (SHT_NOTE).
    Note,
    /// Uninitialized data (SHT_NOBITS).
    Nobits,
    /// Relocations without addends (SHT_REL).
    Rel,
    /// Dynamic linker symbol table (SHT_DYNSYM).
    Dynsym,
    /// Array of constructors (SHT_INIT_ARRAY).
    InitArray,
    /// Array of destructors (SHT_FINI_ARRAY).
    FiniArray,
    /// Preinitialization array (SHT_PREINIT_ARRAY).
    PreinitArray,
    /// Section group (SHT_GROUP).
    Group,
    /// Extended section indexing (SHT_SYMTAB_SHNDX).
    SymtabShndx,
    /// X86-64 unwind information.
    X8664Unwind,
}

impl ElfSectionType {
    /// Get the ELF SHT_* value.
    pub fn elf_value(&self) -> u32 {
        match self {
            ElfSectionType::Null => 0,
            ElfSectionType::Progbits => 1,
            ElfSectionType::Symtab => 2,
            ElfSectionType::Strtab => 3,
            ElfSectionType::Rela => 4,
            ElfSectionType::Hash => 5,
            ElfSectionType::Dynamic => 6,
            ElfSectionType::Note => 7,
            ElfSectionType::Nobits => 8,
            ElfSectionType::Rel => 9,
            ElfSectionType::Dynsym => 11,
            ElfSectionType::InitArray => 14,
            ElfSectionType::FiniArray => 15,
            ElfSectionType::PreinitArray => 16,
            ElfSectionType::Group => 17,
            ElfSectionType::SymtabShndx => 18,
            ElfSectionType::X8664Unwind => 0x7000_0001,
        }
    }
}

/// ELF section flags.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ElfSectionFlags {
    /// Section contains writable data (SHF_WRITE).
    pub write: bool,
    /// Section occupies memory during execution (SHF_ALLOC).
    pub alloc: bool,
    /// Section contains executable instructions (SHF_EXECINSTR).
    pub execinstr: bool,
    /// Section may be merged (SHF_MERGE).
    pub merge: bool,
    /// Section contains null-terminated strings (SHF_STRINGS).
    pub strings: bool,
    /// sh_info contains section header table index (SHF_INFO_LINK).
    pub info_link: bool,
    /// Special ordering requirements (SHF_LINK_ORDER).
    pub link_order: bool,
    /// OS-specific handling (SHF_OS_NONCONFORMING).
    pub os_nonconforming: bool,
    /// Section is a member of a group (SHF_GROUP).
    pub group: bool,
    /// Section holds Thread-Local Storage (SHF_TLS).
    pub tls: bool,
}

impl ElfSectionFlags {
    /// Create default section flags for .text (AX).
    pub fn text() -> Self {
        Self {
            write: false,
            alloc: true,
            execinstr: true,
            merge: false,
            strings: false,
            info_link: false,
            link_order: false,
            os_nonconforming: false,
            group: false,
            tls: false,
        }
    }

    /// Create default section flags for .data (WA).
    pub fn data() -> Self {
        Self {
            write: true,
            alloc: true,
            execinstr: false,
            merge: false,
            strings: false,
            info_link: false,
            link_order: false,
            os_nonconforming: false,
            group: false,
            tls: false,
        }
    }

    /// Create default section flags for .rodata (A).
    pub fn rodata() -> Self {
        Self {
            write: false,
            alloc: true,
            execinstr: false,
            merge: false,
            strings: false,
            info_link: false,
            link_order: false,
            os_nonconforming: false,
            group: false,
            tls: false,
        }
    }

    /// Create default section flags for .bss (WA).
    pub fn bss() -> Self {
        Self {
            write: true,
            alloc: true,
            execinstr: false,
            merge: false,
            strings: false,
            info_link: false,
            link_order: false,
            os_nonconforming: false,
            group: false,
            tls: false,
        }
    }

    /// Compute the ELF sh_flags value.
    pub fn elf_value(&self) -> u64 {
        let mut flags: u64 = 0;
        if self.write {
            flags |= 0x1;
        } // SHF_WRITE
        if self.alloc {
            flags |= 0x2;
        } // SHF_ALLOC
        if self.execinstr {
            flags |= 0x4;
        } // SHF_EXECINSTR
        if self.merge {
            flags |= 0x10;
        } // SHF_MERGE
        if self.strings {
            flags |= 0x20;
        } // SHF_STRINGS
        if self.info_link {
            flags |= 0x40;
        } // SHF_INFO_LINK
        if self.link_order {
            flags |= 0x80;
        } // SHF_LINK_ORDER
        if self.os_nonconforming {
            flags |= 0x100;
        } // SHF_OS_NONCONFORMING
        if self.group {
            flags |= 0x200;
        } // SHF_GROUP
        if self.tls {
            flags |= 0x400;
        } // SHF_TLS
        flags
    }
}

// ============================================================================
// Section Representation
// ============================================================================

/// An ELF section in the object file.
#[derive(Debug, Clone)]
pub struct ElfSection {
    /// Section name (e.g., ".text", ".data").
    pub name: String,
    /// Section type.
    pub section_type: ElfSectionType,
    /// Section flags.
    pub flags: ElfSectionFlags,
    /// Virtual address (for linked objects).
    pub addr: u64,
    /// File offset from the start of the file.
    pub offset: u64,
    /// Section size in bytes.
    pub size: u64,
    /// Section alignment (power of 2).
    pub alignment: u32,
    /// Link to another section index (e.g., symtab for rela).
    pub link: u32,
    /// Additional info (e.g., symbol table index for SHT_SYMTAB).
    pub info: u32,
    /// Entry size for fixed-size entry sections.
    pub entsize: u64,
    /// The section's raw data.
    pub data: Vec<u8>,
    /// Whether this section is finalized.
    pub finalized: bool,
}

impl ElfSection {
    /// Create a new ELF section.
    pub fn new(name: &str, section_type: ElfSectionType, flags: ElfSectionFlags) -> Self {
        Self {
            name: name.to_string(),
            section_type,
            flags,
            addr: 0,
            offset: 0,
            size: 0,
            alignment: 1,
            link: 0,
            info: 0,
            entsize: 0,
            data: Vec::new(),
            finalized: false,
        }
    }

    /// Append raw data to this section.
    pub fn append(&mut self, data: &[u8]) {
        self.data.extend_from_slice(data);
        self.size = self.data.len() as u64;
    }

    /// Append an aligned block of data with NOP padding.
    pub fn append_aligned(&mut self, data: &[u8], alignment: u32) {
        let current_offset = self.data.len() as u64;
        let misalignment = current_offset & (alignment as u64 - 1);
        if misalignment != 0 {
            let padding = alignment as u64 - misalignment;
            let nops = generate_nop_padding(padding as usize, NOPVariant::Intel);
            self.data.extend_from_slice(&nops);
        }
        self.data.extend_from_slice(data);
        self.size = self.data.len() as u64;
    }

    /// Append a u8 value.
    pub fn append_u8(&mut self, value: u8) {
        self.data.push(value);
        self.size = self.data.len() as u64;
    }

    /// Append a u16 value (little-endian).
    pub fn append_u16(&mut self, value: u16) {
        self.data.extend_from_slice(&value.to_le_bytes());
        self.size = self.data.len() as u64;
    }

    /// Append a u32 value (little-endian).
    pub fn append_u32(&mut self, value: u32) {
        self.data.extend_from_slice(&value.to_le_bytes());
        self.size = self.data.len() as u64;
    }

    /// Append a u64 value (little-endian).
    pub fn append_u64(&mut self, value: u64) {
        self.data.extend_from_slice(&value.to_le_bytes());
        self.size = self.data.len() as u64;
    }

    /// Append a signed LEB128 encoded value.
    pub fn append_sleb128(&mut self, value: i64) {
        let encoded = encode_sleb128(value);
        self.data.extend_from_slice(&encoded);
        self.size = self.data.len() as u64;
    }

    /// Append an unsigned LEB128 encoded value.
    pub fn append_uleb128(&mut self, value: u64) {
        let encoded = encode_uleb128(value);
        self.data.extend_from_slice(&encoded);
        self.size = self.data.len() as u64;
    }
}

// ============================================================================
// Symbol Representation
// ============================================================================

/// An ELF symbol.
#[derive(Debug, Clone)]
pub struct ElfSymbol {
    /// Symbol name.
    pub name: String,
    /// Symbol value (address or offset).
    pub value: u64,
    /// Symbol size.
    pub size: u64,
    /// Symbol type (STT_FUNC, STT_OBJECT, etc.).
    pub symbol_type: SymbolType,
    /// Symbol binding (STB_LOCAL, STB_GLOBAL, STB_WEAK).
    pub binding: SymbolBinding,
    /// Symbol visibility.
    pub visibility: SymbolVisibility,
    /// Section index where the symbol is defined.
    pub section_index: u32,
    /// Whether this is an undefined symbol.
    pub is_undefined: bool,
}

/// ELF symbol type (STT_*).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum SymbolType {
    /// Unspecified type (STT_NOTYPE).
    Notype,
    /// Data object (STT_OBJECT).
    Object,
    /// Function (STT_FUNC).
    Func,
    /// Section (STT_SECTION).
    Section,
    /// Source file (STT_FILE).
    File,
    /// Thread-local storage (STT_TLS).
    Tls,
    /// Common block (STT_COMMON).
    Common,
    /// Indirect function (STT_GNU_IFUNC).
    GnuIFunc,
}

impl SymbolType {
    pub fn elf_value(&self) -> u8 {
        match self {
            SymbolType::Notype => 0,
            SymbolType::Object => 1,
            SymbolType::Func => 2,
            SymbolType::Section => 3,
            SymbolType::File => 4,
            SymbolType::Tls => 6,
            SymbolType::Common => 5,
            SymbolType::GnuIFunc => 10,
        }
    }
}

/// ELF symbol binding (STB_*).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum SymbolBinding {
    /// Local symbol (STB_LOCAL).
    Local,
    /// Global symbol (STB_GLOBAL).
    Global,
    /// Weak symbol (STB_WEAK).
    Weak,
    /// GNU unique symbol (STB_GNU_UNIQUE).
    GnuUnique,
}

impl SymbolBinding {
    pub fn elf_value(&self) -> u8 {
        match self {
            SymbolBinding::Local => 0,
            SymbolBinding::Global => 1,
            SymbolBinding::Weak => 2,
            SymbolBinding::GnuUnique => 10,
        }
    }
}

/// ELF symbol visibility.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum SymbolVisibility {
    /// Default visibility (STV_DEFAULT).
    Default,
    /// Internal visibility (STV_INTERNAL).
    Internal,
    /// Hidden visibility (STV_HIDDEN).
    Hidden,
    /// Protected visibility (STV_PROTECTED).
    Protected,
}

impl SymbolVisibility {
    pub fn elf_value(&self) -> u8 {
        match self {
            SymbolVisibility::Default => 0,
            SymbolVisibility::Internal => 1,
            SymbolVisibility::Hidden => 2,
            SymbolVisibility::Protected => 3,
        }
    }
}

impl ElfSymbol {
    /// Create a new function symbol.
    pub fn new_function(name: &str, value: u64, size: u64, section_index: u32) -> Self {
        Self {
            name: name.to_string(),
            value,
            size,
            symbol_type: SymbolType::Func,
            binding: SymbolBinding::Global,
            visibility: SymbolVisibility::Default,
            section_index,
            is_undefined: false,
        }
    }

    /// Create a new local symbol.
    pub fn new_local(name: &str, value: u64, section_index: u32) -> Self {
        Self {
            name: name.to_string(),
            value,
            size: 0,
            symbol_type: SymbolType::Notype,
            binding: SymbolBinding::Local,
            visibility: SymbolVisibility::Default,
            section_index,
            is_undefined: false,
        }
    }

    /// Make this symbol undefined (external reference).
    pub fn as_undefined(mut self) -> Self {
        self.is_undefined = true;
        self.section_index = 0; // SHN_UNDEF
        self
    }
}

// ============================================================================
// Relocation Representation
// ============================================================================

/// An X86-64 ELF relocation entry.
#[derive(Debug, Clone)]
pub struct ElfRelocation {
    /// Offset from the start of the section where the fixup is applied.
    pub offset: u64,
    /// Relocation type (R_X86_64_*).
    pub rel_type: X86RelocationType,
    /// Symbol index this relocation refers to.
    pub symbol_index: u32,
    /// Addend for RELA relocations.
    pub addend: i64,
}

/// X86 relocation types.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum X86RelocationType {
    /// R_X86_64_NONE / R_386_NONE.
    None,
    /// R_X86_64_64: Direct 64-bit.
    Dir64,
    /// R_X86_64_PC32: PC-relative 32-bit.
    PC32,
    /// R_X86_64_GOT32: 32-bit GOT entry.
    Got32,
    /// R_X86_64_PLT32: 32-bit PLT entry.
    Plt32,
    /// R_X86_64_COPY: Copy relocation.
    Copy,
    /// R_X86_64_GLOB_DAT: Create GOT entry.
    GlobDat,
    /// R_X86_64_JUMP_SLOT: Create PLT entry.
    JumpSlot,
    /// R_X86_64_RELATIVE: Adjust by program base.
    Relative,
    /// R_X86_64_GOTPCREL: GOT-relative 32-bit (commonly used).
    GotPcRel,
    /// R_X86_64_32: Direct 32-bit zero-extended.
    Dir32,
    /// R_X86_64_32S: Direct 32-bit sign-extended.
    Dir32S,
    /// R_X86_64_16: Direct 16-bit.
    Dir16,
    /// R_X86_64_PC16: PC-relative 16-bit.
    PC16,
    /// R_X86_64_PC8: PC-relative 8-bit.
    PC8,
    /// R_X86_64_PC64: PC-relative 64-bit.
    PC64,
    /// R_X86_64_GOTPC32: Not used (old alias).
    GotPC32,
    /// R_X86_64_TLSGD: TLS GD.
    TlsGd,
    /// R_X86_64_TLSLD: TLS LD.
    TlsLd,
    /// R_X86_64_TPOFF32: TLS TP offset 32.
    TpOff32,
    /// R_X86_64_GOTTPOFF: TLS IE.
    GotTpOff,
    /// R_X86_64_TLSDESC: TLS DESC.
    TlsDesc,
}

impl X86RelocationType {
    /// Get the ELF relocation type value for x86-64.
    pub fn elf_value_x86_64(&self) -> u32 {
        match self {
            X86RelocationType::None => 0,
            X86RelocationType::Dir64 => 1,
            X86RelocationType::PC32 => 2,
            X86RelocationType::Got32 => 3,
            X86RelocationType::Plt32 => 4,
            X86RelocationType::Copy => 5,
            X86RelocationType::GlobDat => 6,
            X86RelocationType::JumpSlot => 7,
            X86RelocationType::Relative => 8,
            X86RelocationType::GotPcRel => 9,
            X86RelocationType::Dir32 => 10,
            X86RelocationType::Dir32S => 11,
            X86RelocationType::Dir16 => 12,
            X86RelocationType::PC16 => 13,
            X86RelocationType::PC8 => 14,
            X86RelocationType::PC64 => 24,
            X86RelocationType::GotPC32 => 25,
            X86RelocationType::TlsGd => 18,
            X86RelocationType::TlsLd => 19,
            X86RelocationType::TpOff32 => 23,
            X86RelocationType::GotTpOff => 22,
            X86RelocationType::TlsDesc => 36,
        }
    }
}

// ============================================================================
// Constant Island
// ============================================================================

/// A constant island (literal pool) entry.
#[derive(Debug, Clone)]
pub struct ConstantIsland {
    /// Unique ID for this island.
    pub id: usize,
    /// The offset within the section where this island begins.
    pub offset: u64,
    /// The constant values stored in this island.
    pub values: Vec<ConstantIslandEntry>,
    /// The alignment of this island.
    pub alignment: u32,
    /// Whether this island is placed inline (after unconditional branch).
    pub is_inline: bool,
    /// The function this island belongs to.
    pub function_name: String,
}

/// A single entry in a constant island.
#[derive(Debug, Clone)]
pub struct ConstantIslandEntry {
    /// The 64-bit constant value.
    pub value: u64,
    /// The size of the constant (in bytes): 2, 4, 8, or 16.
    pub size: u8,
    /// Whether this entry is referenced PC-relative.
    pub is_pc_rel: bool,
    /// The label/symbol associated with this constant.
    pub label: Option<String>,
}

// ============================================================================
// Jump Table
// ============================================================================

/// A jump table for switch statements.
#[derive(Debug, Clone)]
pub struct JumpTable {
    /// Unique ID for this jump table.
    pub id: usize,
    /// The function this jump table belongs to.
    pub function_name: String,
    /// The jump table entries (target block labels).
    pub entries: Vec<String>,
    /// The entry size (4 or 8 bytes).
    pub entry_size: u32,
    /// The minimum case value (for range checking).
    pub min_case: i64,
    /// The maximum case value (for range checking).
    pub max_case: i64,
    /// The alignment of the jump table.
    pub alignment: u32,
    /// Whether to emit as PC-relative entries.
    pub pc_relative: bool,
    /// The offset where the table is emitted.
    pub offset: u64,
}

// ============================================================================
// CFI / Debug Info
// ============================================================================

/// A CFI (Call Frame Information) directive.
#[derive(Debug, Clone)]
pub enum CFIDirective {
    /// Define CFA offset: CFA = register + offset.
    DefCfa(u16, i64),
    /// Define CFA register (keep offset unchanged).
    DefCfaRegister(u16),
    /// Define CFA offset (keep register unchanged).
    DefCfaOffset(i64),
    /// Define offset of saved register from CFA.
    Offset(u16, i64),
    /// Restore register to the rule at the start of the sequence.
    Restore(u16),
    /// Mark a register as undefined.
    Undefined(u16),
    /// Mark a register as having the same value as another register.
    SameValue(u16),
    /// Mark a register as being saved in another register.
    Register(u16, u16),
    /// Remember current CFA state.
    RememberState,
    /// Restore previously remembered CFA state.
    RestoreState,
    /// Advance the location counter.
    AdvanceLoc(i64),
    /// Advance the location counter by a small amount.
    AdvanceLoc1(u8),
    /// Advance the location counter by a 2-byte amount.
    AdvanceLoc2(u16),
    /// Advance the location counter by a 4-byte amount.
    AdvanceLoc4(u32),
    /// Mark the end of the FDE.
    EndFde,
    /// An expression for computing a value.
    Expression(u16, Vec<u8>),
    /// A val_offset rule.
    ValOffset(u16, i64),
    /// A val_expression rule.
    ValExpression(u16, Vec<u8>),
    /// GNU-specific: window save.
    WindowSave,
    /// GNU-specific: arguments_size.
    ArgumentsSize(i64),
}

/// A DWARF Call Frame Information entry.
#[derive(Debug, Clone)]
pub struct FDE {
    /// The CIE index this FDE uses.
    pub cie_index: u32,
    /// Initial location (start of function).
    pub initial_location: u64,
    /// Address range covered (function size).
    pub address_range: u64,
    /// The CFI directives for this FDE.
    pub directives: Vec<CFIDirective>,
    /// The LSDA (Language-Specific Data Area) address.
    pub lsda: Option<u64>,
    /// The personality function address.
    pub personality: Option<u64>,
    /// Whether this FDE has an LSDA augmentation.
    pub has_lsda: bool,
}

/// A DWARF Common Information Entry.
#[derive(Debug, Clone)]
pub struct CIE {
    /// CIE version.
    pub version: u8,
    /// Augmentation string.
    pub augmentation: String,
    /// Code alignment factor.
    pub code_alignment_factor: u64,
    /// Data alignment factor.
    pub data_alignment_factor: i64,
    /// Return address register.
    pub return_address_register: u16,
    /// Initial CFI directives.
    pub initial_directives: Vec<CFIDirective>,
    /// Whether this CIE has a personality encoding.
    pub has_personality: bool,
    /// The personality encoding byte.
    pub personality_encoding: u8,
    /// Whether this CIE has LSDA encoding.
    pub has_lsda_encoding: bool,
    /// The LSDA encoding byte.
    pub lsda_encoding: u8,
    /// FDE pointer encoding byte.
    pub fde_encoding: u8,
}

// ============================================================================
// LEB128 Encoding
// ============================================================================

/// Encode an unsigned value as ULEB128.
pub fn encode_uleb128(value: u64) -> Vec<u8> {
    let mut result: Vec<u8> = Vec::new();
    let mut val = value;
    loop {
        let mut byte = (val & 0x7F) as u8;
        val >>= 7;
        if val != 0 {
            byte |= 0x80;
        }
        result.push(byte);
        if val == 0 {
            break;
        }
    }
    result
}

/// Encode a signed value as SLEB128.
pub fn encode_sleb128(value: i64) -> Vec<u8> {
    let mut result: Vec<u8> = Vec::new();
    let mut val = value;
    let mut more = true;

    while more {
        let mut byte = (val & 0x7F) as u8;
        val >>= 7;

        // Sign bit of byte is second high-order bit:
        // 0xxxxxxx if this is the last byte and the value is non-negative
        // 1xxxxxxx if this is not the last byte
        if (val == 0 && (byte & 0x40) == 0) || (val == -1 && (byte & 0x40) != 0) {
            more = false;
        } else {
            byte |= 0x80;
        }
        result.push(byte);
    }
    result
}

// ============================================================================
// NOP Padding Generation
// ============================================================================

/// Generate a NOP padding sequence of the specified length.
pub fn generate_nop_padding(length: usize, variant: NOPVariant) -> Vec<u8> {
    if length == 0 {
        return Vec::new();
    }

    let mut result: Vec<u8> = Vec::with_capacity(length);
    let mut remaining = length;

    match variant {
        NOPVariant::Intel => {
            while remaining > 0 {
                let nop = match remaining {
                    1 => NOP1,
                    2 => NOP2_INTEL,
                    3 => NOP3_INTEL,
                    4 => NOP4_INTEL,
                    5 => NOP5_INTEL,
                    6 => NOP6_INTEL,
                    7 => NOP7_INTEL,
                    8 => NOP8_INTEL,
                    9 => NOP9_INTEL,
                    10 => NOP10_INTEL,
                    11 => NOP11_INTEL,
                    12 => NOP12_INTEL,
                    13 => NOP13_INTEL,
                    14 => NOP14_INTEL,
                    _ => NOP15_INTEL,
                };
                let take = nop.len().min(remaining);
                result.extend_from_slice(&nop[..take]);
                remaining -= take;
            }
        }
        NOPVariant::Amd => {
            // AMD recommended: prefer 0F 1F-based NOPs for length >= 3.
            while remaining > 0 {
                let nop = match remaining {
                    1 => NOP1,
                    2 => NOP2_INTEL,
                    3 => NOP3_INTEL,
                    4 => NOP4_INTEL,
                    5..=15 => {
                        // For AMD, longer NOPs use the standard Intel patterns
                        // except for length 5 which may use 66 66 90 66 90.
                        NOP5_INTEL
                    }
                    _ => NOP15_INTEL,
                };
                let take = nop.len().min(remaining);
                result.extend_from_slice(&nop[..take]);
                remaining -= take;
            }
        }
        NOPVariant::SingleByte => {
            result.resize(length, 0x90);
        }
        NOPVariant::LongNop => {
            // Long NOP: 0x66 prefix repeated, then 0x90.
            while remaining > 1 {
                result.push(0x66);
                remaining -= 1;
            }
            if remaining == 1 {
                result.push(0x90);
            }
        }
    }

    result
}

/// Align an offset to a given alignment boundary and return the NOP padding.
pub fn generate_alignment_padding(
    current_offset: u64,
    alignment: u32,
    variant: NOPVariant,
) -> Vec<u8> {
    let alignment = alignment as u64;
    if alignment <= 1 {
        return Vec::new();
    }
    let misalignment = current_offset & (alignment - 1);
    if misalignment == 0 {
        return Vec::new();
    }
    let padding = (alignment - misalignment) as usize;
    generate_nop_padding(padding, variant)
}

// ============================================================================
// DWARF Line Number Program
// ============================================================================

/// DWARF line number program state machine.
#[derive(Debug, Clone)]
pub struct DwarfLineProgram {
    /// The raw bytecode for the line number program.
    pub bytecode: Vec<u8>,
    /// Standard opcode length array (DW_LNS_*).
    pub standard_opcode_lengths: Vec<u8>,
    /// Minimum instruction length.
    pub minimum_instruction_length: u8,
    /// Maximum operations per instruction.
    pub maximum_operations_per_instruction: u8,
    /// Default is_stmt value.
    pub default_is_stmt: bool,
    /// Line base (signed).
    pub line_base: i8,
    /// Line range.
    pub line_range: u8,
    /// Opcode base.
    pub opcode_base: u8,
}

impl DwarfLineProgram {
    /// Create a new DWARF line number program.
    pub fn new() -> Self {
        Self {
            bytecode: Vec::new(),
            standard_opcode_lengths: vec![0; 12], // DW_LNS_set_isa is 12
            minimum_instruction_length: 1,
            maximum_operations_per_instruction: 1,
            default_is_stmt: true,
            line_base: -5,
            line_range: 14,
            opcode_base: 13, // Next after the last standard opcode.
        }
    }

    /// Emit a special opcode (line and address advance).
    pub fn emit_special_opcode(&mut self, line_advance: i32, addr_advance: u32) {
        let adjusted_line = line_advance - self.line_base as i32;
        if adjusted_line >= 0 && adjusted_line < self.line_range as i32 && addr_advance < 256 {
            let opcode = (adjusted_line as u8) + (self.line_range * addr_advance as u8);
            let special = opcode + self.opcode_base;
            self.bytecode.push(special);
        }
    }

    /// Emit DW_LNS_copy.
    pub fn emit_copy(&mut self) {
        self.bytecode.push(0x01); // DW_LNS_copy
    }

    /// Emit DW_LNS_advance_pc.
    pub fn emit_advance_pc(&mut self, advance: u64) {
        self.bytecode.push(0x02); // DW_LNS_advance_pc
        self.bytecode.extend_from_slice(&encode_uleb128(advance));
    }

    /// Emit DW_LNS_advance_line.
    pub fn emit_advance_line(&mut self, advance: i64) {
        self.bytecode.push(0x03); // DW_LNS_advance_line
        self.bytecode.extend_from_slice(&encode_sleb128(advance));
    }

    /// Emit DW_LNS_set_file.
    pub fn emit_set_file(&mut self, file_index: u64) {
        self.bytecode.push(0x04); // DW_LNS_set_file
        self.bytecode.extend_from_slice(&encode_uleb128(file_index));
    }

    /// Emit DW_LNS_set_column.
    pub fn emit_set_column(&mut self, column: u64) {
        self.bytecode.push(0x05); // DW_LNS_set_column
        self.bytecode.extend_from_slice(&encode_uleb128(column));
    }

    /// Emit DW_LNE_end_sequence.
    pub fn emit_end_sequence(&mut self) {
        self.bytecode.push(0x00); // Extended opcode
        self.bytecode.extend_from_slice(&encode_uleb128(1)); // Length
        self.bytecode.push(0x01); // DW_LNE_end_sequence
    }

    /// Emit DW_LNE_set_address.
    pub fn emit_set_address(&mut self, addr: u64) {
        self.bytecode.push(0x00); // Extended opcode
        self.bytecode.extend_from_slice(&encode_uleb128(9)); // Length = 1 + 8
        self.bytecode.push(0x02); // DW_LNE_set_address
        self.bytecode.extend_from_slice(&addr.to_le_bytes());
    }

    /// Emit DW_LNE_define_file.
    pub fn emit_define_file(&mut self, name: &str, dir_index: u64, mtime: u64, size: u64) {
        let mut payload: Vec<u8> = Vec::new();
        payload.extend_from_slice(name.as_bytes());
        payload.push(0); // Null terminator
        payload.extend_from_slice(&encode_uleb128(dir_index));
        payload.extend_from_slice(&encode_uleb128(mtime));
        payload.extend_from_slice(&encode_uleb128(size));

        self.bytecode.push(0x00); // Extended opcode
        self.bytecode
            .extend_from_slice(&encode_uleb128(1 + payload.len() as u64));
        self.bytecode.push(0x03); // DW_LNE_define_file
        self.bytecode.extend_from_slice(&payload);
    }

    /// Get the total bytecode length.
    pub fn len(&self) -> usize {
        self.bytecode.len()
    }

    /// Whether the program is empty.
    pub fn is_empty(&self) -> bool {
        self.bytecode.is_empty()
    }
}

// ============================================================================
// Exception Tables
// ============================================================================

/// A GCC except-table (LSDA) call site entry.
#[derive(Debug, Clone)]
pub struct LsdaCallSite {
    /// Start offset relative to the function start.
    pub start_offset: u32,
    /// Length of the call site region.
    pub length: u32,
    /// Landing pad offset (0 if none).
    pub landing_pad: u32,
    /// Action table index (0 if no action).
    pub action_index: u32,
}

/// A landing pad action entry.
#[derive(Debug, Clone)]
pub struct LsdaAction {
    /// Type filter index (positive = catch type, negative = exception spec).
    pub type_filter: i32,
    /// Next action offset (0 if last action).
    pub next_action_offset: i32,
}

/// A complete LSDA (Language-Specific Data Area).
#[derive(Debug, Clone)]
pub struct Lsda {
    /// Landing pad base (offset from function start).
    pub landing_pad_base: u32,
    /// Type table pointer encoding.
    pub ttype_encoding: u8,
    /// Type table entries (symbol names).
    pub type_table: Vec<String>,
    /// Call site table entries.
    pub call_sites: Vec<LsdaCallSite>,
    /// Action table entries.
    pub actions: Vec<LsdaAction>,
    /// Whether this LSDA uses the "SJLJ" (setjmp/longjmp) format.
    pub is_sjlj: bool,
}

impl Lsda {
    /// Create a new empty LSDA.
    pub fn new() -> Self {
        Self {
            landing_pad_base: 0,
            ttype_encoding: 0x9B, // DW_EH_PE_indirect | DW_EH_PE_pcrel | DW_EH_PE_sdata4
            type_table: Vec::new(),
            call_sites: Vec::new(),
            actions: Vec::new(),
            is_sjlj: false,
        }
    }

    /// Encode the LSDA as a sequence of bytes.
    pub fn encode(&self) -> Vec<u8> {
        let mut data: Vec<u8> = Vec::new();

        // Landing pad base
        data.push(self.landing_pad_base as u8);

        // TType encoding
        data.push(self.ttype_encoding);

        // TType base offset (ULEB128 encoded, relative to the
        // start of the type table in the call site table)
        if !self.type_table.is_empty() {
            data.extend_from_slice(&encode_uleb128(0)); // Offset to type table
        } else {
            data.push(0);
        }

        // Call site table length (ULEB128).
        let cst_len = self.call_sites.len() as u64;
        data.extend_from_slice(&encode_uleb128(cst_len));

        // Call site entries.
        for site in &self.call_sites {
            data.extend_from_slice(&encode_uleb128(site.start_offset as u64));
            data.extend_from_slice(&encode_uleb128(site.length as u64));
            data.extend_from_slice(&encode_uleb128(site.landing_pad as u64));
            data.extend_from_slice(&encode_uleb128(site.action_index as u64));
        }

        data
    }
}

// ============================================================================
// Main Emitter: X86CodeEmission
// ============================================================================

/// The primary code emission preparation pass for X86 targets.
#[derive(Debug, Clone)]
pub struct X86CodeEmission {
    /// Target triple.
    pub target_triple: String,
    /// Whether targeting 64-bit mode.
    pub is_64bit: bool,
    /// Configuration.
    pub config: CodeEmissionConfig,
    /// Sections of the object file.
    pub sections: HashMap<String, ElfSection>,
    /// Section ordering for emission.
    pub section_order: Vec<String>,
    /// Symbols defined in the object file.
    pub symbols: Vec<ElfSymbol>,
    /// Relocations to apply.
    pub relocations: Vec<ElfRelocation>,
    /// Constant islands to emit.
    pub constant_islands: Vec<ConstantIsland>,
    /// Jump tables to emit.
    pub jump_tables: Vec<JumpTable>,
    /// The text section name (".text" or custom).
    pub text_section: String,
    /// The data section name.
    pub data_section: String,
    /// The read-only data section name.
    pub rodata_section: String,
    /// Current section being emitted to.
    pub current_section: Option<String>,
    /// Current offset in the text section.
    pub text_offset: u64,
    /// Statistics.
    pub stats: CodeEmissionStats,
}

/// Configuration for code emission.
#[derive(Debug, Clone)]
pub struct CodeEmissionConfig {
    /// Function alignment.
    pub function_alignment: u32,
    /// Loop alignment.
    pub loop_alignment: u32,
    /// Basic block alignment.
    pub block_alignment: u32,
    /// Constant island alignment.
    pub constant_island_alignment: u32,
    /// Jump table alignment.
    pub jump_table_alignment: u32,
    /// NOP variant to use.
    pub nop_variant: NOPVariant,
    /// Emit debug line information.
    pub emit_debug_line: bool,
    /// Emit CFI directives.
    pub emit_cfi: bool,
    /// Emit exception tables.
    pub emit_eh_tables: bool,
    /// Optimize NOP alignment for performance.
    pub optimize_alignments: bool,
    /// Use compact unwind on macOS.
    pub compact_unwind: bool,
    /// Target OS.
    pub target_os: TargetOs,
}

/// Target operating system for code emission.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TargetOs {
    Linux,
    MacOS,
    Windows,
    FreeBSD,
    Unknown,
}

impl Default for CodeEmissionConfig {
    fn default() -> Self {
        Self {
            function_alignment: DEFAULT_FUNCTION_ALIGNMENT,
            loop_alignment: DEFAULT_LOOP_ALIGNMENT,
            block_alignment: DEFAULT_BLOCK_ALIGNMENT,
            constant_island_alignment: CONSTANT_ISLAND_ALIGNMENT,
            jump_table_alignment: 8,
            nop_variant: NOPVariant::Intel,
            emit_debug_line: false,
            emit_cfi: false,
            emit_eh_tables: false,
            optimize_alignments: true,
            compact_unwind: false,
            target_os: TargetOs::Linux,
        }
    }
}

/// Statistics collected during code emission.
#[derive(Debug, Clone, Default)]
pub struct CodeEmissionStats {
    /// Number of functions emitted.
    pub functions_emitted: usize,
    /// Number of basic blocks emitted.
    pub blocks_emitted: usize,
    /// Total bytes of code emitted.
    pub code_bytes: u64,
    /// Total bytes of data emitted.
    pub data_bytes: u64,
    /// Number of NOP bytes emitted for alignment.
    pub nop_bytes: u64,
    /// Number of constant islands emitted.
    pub constant_islands: usize,
    /// Number of jump tables emitted.
    pub jump_tables: usize,
    /// Number of relocations emitted.
    pub relocations_count: usize,
    /// Number of symbols emitted.
    pub symbols_count: usize,
    /// Total debug info bytes.
    pub debug_bytes: u64,
}

// ============================================================================
// X86CodeEmission Implementation
// ============================================================================

impl X86CodeEmission {
    /// Create a new code emission preparer for x86-64.
    pub fn new_x86_64(target: &str) -> Self {
        let target_os = if target.contains("linux") {
            TargetOs::Linux
        } else if target.contains("darwin") || target.contains("macos") {
            TargetOs::MacOS
        } else if target.contains("windows") {
            TargetOs::Windows
        } else if target.contains("freebsd") {
            TargetOs::FreeBSD
        } else {
            TargetOs::Unknown
        };

        Self {
            target_triple: target.to_string(),
            is_64bit: true,
            config: CodeEmissionConfig::default(),
            sections: HashMap::new(),
            section_order: Vec::new(),
            symbols: Vec::new(),
            relocations: Vec::new(),
            constant_islands: Vec::new(),
            jump_tables: Vec::new(),
            text_section: ".text".to_string(),
            data_section: ".data".to_string(),
            rodata_section: ".rodata".to_string(),
            current_section: None,
            text_offset: 0,
            stats: CodeEmissionStats::default(),
        }
    }

    /// Create a new code emission preparer for x86-32.
    pub fn new_x86_32(target: &str) -> Self {
        let mut emitter = Self::new_x86_64(target);
        emitter.is_64bit = false;
        emitter
    }

    /// Set custom configuration.
    pub fn with_config(mut self, config: CodeEmissionConfig) -> Self {
        self.config = config;
        self
    }

    // ========================================================================
    // Full Emission Pipeline
    // ========================================================================

    /// Run the full code emission preparation on a function.
    pub fn prepare_function(&mut self, mf: &MachineFunction) {
        self.stats.functions_emitted += 1;
        self.stats.blocks_emitted += mf.blocks.len();

        // Ensure we're in the text section.
        self.switch_to_section(&self.text_section.clone());

        // Emit function alignment.
        self.emit_function_alignment(mf);

        // Emit function symbol.
        self.emit_symbol(&mf.name, self.text_offset, mf.blocks.len() as u64 * 16);

        // Emit function body.
        for block in &mf.blocks {
            // Optionally emit block alignment.
            if self.config.optimize_alignments {
                self.emit_block_alignment();
            }

            // Emit block code.
            for _instr in &block.instructions {
                // In a full implementation, encode each instruction to bytes
                // and append to the text section.
                self.stats.code_bytes += 4; // Average instruction size estimate.
            }
        }

        // Emit constant islands near this function if needed.
        self.emit_constant_islands_for_function(mf);

        // Emit jump tables for this function if needed.
        self.emit_jump_tables_for_function(mf);

        // Emit CFI directives if enabled.
        if self.config.emit_cfi {
            self.emit_cfi_for_function(mf);
        }

        // Emit debug line info if enabled.
        if self.config.emit_debug_line {
            self.emit_debug_line_for_function(mf);
        }

        // Emit exception handling tables if enabled.
        if self.config.emit_eh_tables {
            self.emit_eh_for_function(mf);
        }
    }

    // ========================================================================
    // Section Management
    // ========================================================================

    /// Switch to a named section, creating it if necessary.
    pub fn switch_to_section(&mut self, name: &str) {
        if self.current_section.as_deref() == Some(name) {
            return; // Already in this section.
        }

        if !self.sections.contains_key(name) {
            self.create_section(name);
        }

        self.current_section = Some(name.to_string());
    }

    /// Create a new section with appropriate flags.
    fn create_section(&mut self, name: &str) {
        let (section_type, flags) = self.section_defaults(name);
        let section = ElfSection::new(name, section_type, flags);

        if !self.section_order.contains(&name.to_string()) {
            self.section_order.push(name.to_string());
        }

        self.sections.insert(name.to_string(), section);
    }

    /// Get default section type and flags based on section name.
    fn section_defaults(&self, name: &str) -> (ElfSectionType, ElfSectionFlags) {
        match name {
            ".text" | ".text.hot" | ".text.startup" | ".text.unlikely" => {
                (ElfSectionType::Progbits, ElfSectionFlags::text())
            }
            ".data" | ".data.rel" | ".data.rel.ro" => {
                (ElfSectionType::Progbits, ElfSectionFlags::data())
            }
            ".rodata" | ".rodata.str1.1" | ".rodata.cst4" | ".rodata.cst8" | ".rodata.cst16" => {
                (ElfSectionType::Progbits, ElfSectionFlags::rodata())
            }
            ".bss" => (ElfSectionType::Nobits, ElfSectionFlags::bss()),
            ".eh_frame" => (
                ElfSectionType::X8664Unwind,
                ElfSectionFlags {
                    write: false,
                    alloc: true,
                    execinstr: false,
                    merge: false,
                    strings: false,
                    info_link: false,
                    link_order: false,
                    os_nonconforming: false,
                    group: false,
                    tls: false,
                },
            ),
            ".debug_line" | ".debug_info" | ".debug_abbrev" | ".debug_str" | ".debug_loc"
            | ".debug_ranges" => (
                ElfSectionType::Progbits,
                ElfSectionFlags {
                    write: false,
                    alloc: false,
                    execinstr: false,
                    merge: false,
                    strings: false,
                    info_link: false,
                    link_order: false,
                    os_nonconforming: false,
                    group: false,
                    tls: false,
                },
            ),
            ".symtab" => (
                ElfSectionType::Symtab,
                ElfSectionFlags {
                    write: false,
                    alloc: false,
                    execinstr: false,
                    merge: false,
                    strings: false,
                    info_link: false,
                    link_order: false,
                    os_nonconforming: false,
                    group: false,
                    tls: false,
                },
            ),
            ".strtab" => (
                ElfSectionType::Strtab,
                ElfSectionFlags {
                    write: false,
                    alloc: false,
                    execinstr: false,
                    merge: false,
                    strings: false,
                    info_link: false,
                    link_order: false,
                    os_nonconforming: false,
                    group: false,
                    tls: false,
                },
            ),
            ".rela.text" | ".rela.data" | ".rela.eh_frame" => (
                ElfSectionType::Rela,
                ElfSectionFlags {
                    write: false,
                    alloc: false,
                    execinstr: false,
                    merge: false,
                    strings: false,
                    info_link: true,
                    link_order: false,
                    os_nonconforming: false,
                    group: false,
                    tls: false,
                },
            ),
            _ => (
                ElfSectionType::Progbits,
                ElfSectionFlags {
                    write: false,
                    alloc: false,
                    execinstr: false,
                    merge: false,
                    strings: false,
                    info_link: false,
                    link_order: false,
                    os_nonconforming: false,
                    group: false,
                    tls: false,
                },
            ),
        }
    }

    // ========================================================================
    // Alignment Emission
    // ========================================================================

    /// Emit function entry alignment padding.
    pub fn emit_function_alignment(&mut self, _mf: &MachineFunction) {
        if self.config.function_alignment > 1 {
            let padding = generate_alignment_padding(
                self.text_offset,
                self.config.function_alignment,
                self.config.nop_variant,
            );
            if !padding.is_empty() {
                self.stats.nop_bytes += padding.len() as u64;
                self.append_to_current_section(&padding);
                self.text_offset += padding.len() as u64;
            }
        }
    }

    /// Emit basic block alignment padding.
    fn emit_block_alignment(&mut self) {
        if self.config.block_alignment > 1 {
            let padding = generate_alignment_padding(
                self.text_offset,
                self.config.block_alignment,
                self.config.nop_variant,
            );
            if !padding.is_empty() {
                self.stats.nop_bytes += padding.len() as u64;
                self.append_to_current_section(&padding);
                self.text_offset += padding.len() as u64;
            }
        }
    }

    /// Emit loop alignment padding (larger NOPs for loop tops).
    pub fn emit_loop_alignment(&mut self) {
        if self.config.loop_alignment > 1 {
            let padding = generate_alignment_padding(
                self.text_offset,
                self.config.loop_alignment,
                self.config.nop_variant,
            );
            if !padding.is_empty() {
                self.stats.nop_bytes += padding.len() as u64;
                self.append_to_current_section(&padding);
                self.text_offset += padding.len() as u64;
            }
        }
    }

    // ========================================================================
    // Constant Island Emission
    // ========================================================================

    /// Register a constant island for later emission.
    pub fn add_constant_island(&mut self, island: ConstantIsland) {
        self.constant_islands.push(island);
        self.stats.constant_islands += 1;
    }

    /// Emit all constant islands for a specific function.
    fn emit_constant_islands_for_function(&mut self, mf: &MachineFunction) {
        let func_name = &mf.name;
        let islands: Vec<usize> = self
            .constant_islands
            .iter()
            .enumerate()
            .filter(|(_, ci)| ci.function_name == *func_name)
            .map(|(i, _)| i)
            .collect();

        if islands.is_empty() {
            return;
        }

        // For inline islands: emit after an unconditional JMP at the
        // end of the function.
        // For separate islands: emit in the .rodata section.
        for idx in islands {
            let island = &self.constant_islands[idx];
            if island.is_inline {
                // Emit inline in .text section.
                let alignment = island.alignment;
                let padding = generate_alignment_padding(
                    self.text_offset,
                    alignment,
                    self.config.nop_variant,
                );
                self.append_to_current_section(&padding);
                self.text_offset += padding.len() as u64;

                for entry in &island.values {
                    match entry.size {
                        4 => {
                            self.append_u32_to_current_section(entry.value as u32);
                            self.text_offset += 4;
                        }
                        8 => {
                            self.append_u64_to_current_section(entry.value);
                            self.text_offset += 8;
                        }
                        _ => {
                            self.append_u64_to_current_section(entry.value);
                            self.text_offset += 8;
                        }
                    }
                }
                self.stats.data_bytes += island.values.len() as u64 * 8;
            } else {
                // Emit in rodata section.
                self.switch_to_section(&self.rodata_section);
                let alignment = island.alignment;
                let padding = generate_alignment_padding(
                    self.sections
                        .get(&self.rodata_section)
                        .map_or(0, |s| s.size),
                    alignment,
                    self.config.nop_variant,
                );
                self.append_to_current_section(&padding);

                for entry in &island.values {
                    match entry.size {
                        4 => {
                            self.append_u32_to_current_section(entry.value as u32);
                        }
                        8 => {
                            self.append_u64_to_current_section(entry.value);
                        }
                        _ => {
                            self.append_u64_to_current_section(entry.value);
                        }
                    }
                }
                self.switch_to_section(&self.text_section);
                self.stats.data_bytes += island.values.len() as u64 * 8;
            }
        }
    }

    // ========================================================================
    // Jump Table Emission
    // ========================================================================

    /// Register a jump table for later emission.
    pub fn add_jump_table(&mut self, table: JumpTable) {
        self.jump_tables.push(table);
        self.stats.jump_tables += 1;
    }

    /// Emit jump tables for a specific function.
    fn emit_jump_tables_for_function(&mut self, mf: &MachineFunction) {
        let func_name = &mf.name;
        let tables: Vec<usize> = self
            .jump_tables
            .iter()
            .enumerate()
            .filter(|(_, jt)| jt.function_name == *func_name)
            .map(|(i, _)| i)
            .collect();

        if tables.is_empty() {
            return;
        }

        // Jump tables are typically emitted in .rodata or .text.
        self.switch_to_section(&self.rodata_section);

        for idx in tables {
            let table = &self.jump_tables[idx];
            let alignment = table.alignment;
            let current_size = self
                .sections
                .get(&self.rodata_section)
                .map_or(0, |s| s.size);
            let padding =
                generate_alignment_padding(current_size, alignment, self.config.nop_variant);
            self.append_to_current_section(&padding);

            for _entry in &table.entries {
                // Emit the target address (or PC-relative offset) for each entry.
                if table.entry_size == 8 {
                    self.append_u64_to_current_section(0); // Placeholder; filled by relocation.
                } else {
                    self.append_u32_to_current_section(0); // Placeholder; filled by relocation.
                }
            }
            self.stats.data_bytes += table.entries.len() as u64 * table.entry_size as u64;
        }

        self.switch_to_section(&self.text_section);
    }

    // ========================================================================
    // Symbol Emission
    // ========================================================================

    /// Emit a symbol definition.
    pub fn emit_symbol(&mut self, name: &str, value: u64, size: u64) {
        let section_index = self.get_current_section_index();
        let symbol = ElfSymbol::new_function(name, value, size, section_index);
        self.symbols.push(symbol);
        self.stats.symbols_count += 1;
    }

    /// Emit an undefined symbol reference (relocation).
    pub fn emit_relocation(
        &mut self,
        offset: u64,
        rel_type: X86RelocationType,
        symbol_name: &str,
        addend: i64,
    ) {
        // Find or create the symbol.
        let symbol_index = self.find_or_create_symbol(symbol_name);

        self.relocations.push(ElfRelocation {
            offset,
            rel_type,
            symbol_index,
            addend,
        });
        self.stats.relocations_count += 1;
    }

    /// Find or create a symbol by name.
    fn find_or_create_symbol(&mut self, name: &str) -> u32 {
        if let Some(pos) = self.symbols.iter().position(|s| s.name == name) {
            pos as u32
        } else {
            let idx = self.symbols.len() as u32;
            let sym = ElfSymbol {
                name: name.to_string(),
                value: 0,
                size: 0,
                symbol_type: SymbolType::Notype,
                binding: SymbolBinding::Global,
                visibility: SymbolVisibility::Default,
                section_index: 0,
                is_undefined: true,
            };
            self.symbols.push(sym);
            self.stats.symbols_count += 1;
            idx
        }
    }

    // ========================================================================
    // CFI Emission
    // ========================================================================

    /// Emit CFI directives for a function.
    fn emit_cfi_for_function(&mut self, mf: &MachineFunction) {
        let fde = self.build_fde_for_function(mf);

        self.switch_to_section(".eh_frame");

        // CIE
        let cie = CIE {
            version: 1,
            augmentation: "zR".to_string(),
            code_alignment_factor: 1,
            data_alignment_factor: if self.is_64bit { -8 } else { -4 },
            return_address_register: if self.is_64bit { 16 } else { 8 }, // RA/RIP
            initial_directives: Vec::new(),
            has_personality: false,
            personality_encoding: 0,
            has_lsda_encoding: false,
            lsda_encoding: 0,
            fde_encoding: 0x1B, // DW_EH_PE_pcrel | DW_EH_PE_sdata4
        };

        // Encode CIE + FDE into the .eh_frame section.
        let encoded = self.encode_eh_frame(&cie, &fde);
        self.append_to_current_section(&encoded);
        self.stats.debug_bytes += encoded.len() as u64;

        self.switch_to_section(&self.text_section);
    }

    /// Build an FDE for a function.
    fn build_fde_for_function(&self, mf: &MachineFunction) -> FDE {
        let mut directives: Vec<CFIDirective> = Vec::new();

        // Standard prologue CFI directives.
        // push rbp
        if self.is_64bit {
            directives.push(CFIDirective::DefCfaOffset(16));
            directives.push(CFIDirective::Offset(RBP, -16));
            // mov rbp, rsp
            directives.push(CFIDirective::DefCfaRegister(RBP));
        }

        // Callee-saved register saves.
        // ... (depends on frame lowering).

        FDE {
            cie_index: 0,
            initial_location: 0,                        // Filled by relocation.
            address_range: mf.blocks.len() as u64 * 16, // Estimated function size.
            directives,
            lsda: None,
            personality: None,
            has_lsda: false,
        }
    }

    /// Encode CIE + FDE into raw bytes for the .eh_frame section.
    fn encode_eh_frame(&self, cie: &CIE, fde: &FDE) -> Vec<u8> {
        let mut data: Vec<u8> = Vec::new();

        // CIE length (placeholder, will be filled later).
        data.extend_from_slice(&0u32.to_le_bytes());
        // CIE id = 0.
        data.extend_from_slice(&0u32.to_le_bytes());
        // Version.
        data.push(cie.version);
        // Augmentation string.
        data.extend_from_slice(cie.augmentation.as_bytes());
        data.push(0);
        // Code alignment factor.
        data.extend_from_slice(&encode_uleb128(cie.code_alignment_factor));
        // Data alignment factor.
        data.extend_from_slice(&encode_sleb128(cie.data_alignment_factor));
        // Return address register.
        data.push(cie.return_address_register as u8);

        // ... Initial directives, augmentation data, etc.

        // FDE
        // FDE length.
        data.extend_from_slice(&0u32.to_le_bytes());
        // CIE pointer (relocation).
        data.extend_from_slice(&0i32.to_le_bytes());
        // Initial location (relocation).
        data.extend_from_slice(&0i32.to_le_bytes());
        // Address range.
        data.extend_from_slice(&(fde.address_range as u32).to_le_bytes());

        // CFI instructions.
        for directive in &fde.directives {
            match directive {
                CFIDirective::DefCfaOffset(offset) => {
                    data.push(0x0F); // DW_CFA_def_cfa_offset
                    data.extend_from_slice(&encode_uleb128(*offset as u64));
                }
                CFIDirective::DefCfaRegister(reg) => {
                    data.push(0x0D); // DW_CFA_def_cfa_register
                    data.extend_from_slice(&encode_uleb128(*reg as u64));
                }
                CFIDirective::Offset(reg, offset) => {
                    data.push(0x80 | (reg & 0x3F) as u8); // DW_CFA_offset
                    data.extend_from_slice(&encode_uleb128(*offset as u64));
                }
                CFIDirective::DefCfa(reg, offset) => {
                    data.push(0x0C); // DW_CFA_def_cfa
                    data.extend_from_slice(&encode_uleb128(*reg as u64));
                    data.extend_from_slice(&encode_uleb128(*offset as u64));
                }
                _ => {
                    // Placeholder for other CFI directives.
                }
            }
        }

        data
    }

    // ========================================================================
    // Debug Line Emission
    // ========================================================================

    /// Emit debug line info for a function.
    fn emit_debug_line_for_function(&mut self, _mf: &MachineFunction) {
        if !self.config.emit_debug_line {
            return;
        }

        let mut program = DwarfLineProgram::new();

        // Emit a line program for this function.
        // In a full implementation, this would contain address/line mappings
        // for each instruction.

        if !program.is_empty() {
            self.switch_to_section(".debug_line");
            self.append_to_current_section(&program.bytecode);
            self.stats.debug_bytes += program.bytecode.len() as u64;
            self.switch_to_section(&self.text_section);
        }
    }

    // ========================================================================
    // Exception Table Emission
    // ========================================================================

    /// Emit exception handling tables for a function.
    fn emit_eh_for_function(&mut self, mf: &MachineFunction) {
        if !self.config.emit_eh_tables {
            return;
        }

        let lsda = self.build_lsda_for_function(mf);
        let encoded = lsda.encode();

        if !encoded.is_empty() {
            self.switch_to_section(".gcc_except_table");
            self.append_to_current_section(&encoded);
            self.stats.debug_bytes += encoded.len() as u64;
            self.switch_to_section(&self.text_section);
        }
    }

    /// Build an LSDA for a function with exception handling.
    fn build_lsda_for_function(&self, _mf: &MachineFunction) -> Lsda {
        // Scan the function for landing pads, catch blocks, and cleanup blocks.
        let mut lsda = Lsda::new();
        // In a full implementation, analyze EH labels and build
        // call site table and action table.
        lsda
    }

    // ========================================================================
    // Section Data Append Helpers
    // ========================================================================

    /// Append raw data to the current section.
    fn append_to_current_section(&mut self, data: &[u8]) {
        if let Some(ref name) = self.current_section.clone() {
            if let Some(section) = self.sections.get_mut(name) {
                section.append(data);
            }
        }
    }

    /// Append a u32 to the current section.
    fn append_u32_to_current_section(&mut self, value: u32) {
        if let Some(ref name) = self.current_section.clone() {
            if let Some(section) = self.sections.get_mut(name) {
                section.append_u32(value);
            }
        }
    }

    /// Append a u64 to the current section.
    fn append_u64_to_current_section(&mut self, value: u64) {
        if let Some(ref name) = self.current_section.clone() {
            if let Some(section) = self.sections.get_mut(name) {
                section.append_u64(value);
            }
        }
    }

    // ========================================================================
    // Section Organization
    // ========================================================================

    /// Get the current section index (0 = undefined).
    fn get_current_section_index(&self) -> u32 {
        if let Some(ref name) = self.current_section {
            self.section_order
                .iter()
                .position(|n| n == name)
                .map_or(0, |i| (i + 1) as u32)
        } else {
            0
        }
    }

    /// Finalize all sections for writing the object file.
    pub fn finalize_sections(&mut self) {
        // Compute offsets for each section.
        let mut offset: u64 = 0;

        // ELF header space (64 bytes for Elf64_Ehdr).
        offset += 64;

        // Reserve space for section header table.
        let shdr_size: u64 = if self.is_64bit { 64 } else { 40 };
        let num_sections = self.section_order.len() + 1; // +1 for null section
        offset += shdr_size * num_sections as u64;

        for name in &self.section_order.clone() {
            if let Some(section) = self.sections.get_mut(name) {
                // Align section start.
                let align = section.alignment as u64;
                if align > 1 {
                    let misalign = offset & (align - 1);
                    if misalign != 0 {
                        offset += align - misalign;
                    }
                }
                section.offset = offset;
                offset += section.size;
                section.finalized = true;
            }
        }
    }

    /// Generate a report string.
    pub fn report(&self) -> String {
        format!(
            "CodeEmission: funcs={} blocks={} code_bytes={} data_bytes={} nop_bytes={} \
             const_islands={} jump_tables={} relocs={} symbols={} debug_bytes={} sections={}",
            self.stats.functions_emitted,
            self.stats.blocks_emitted,
            self.stats.code_bytes,
            self.stats.data_bytes,
            self.stats.nop_bytes,
            self.stats.constant_islands,
            self.stats.jump_tables,
            self.stats.relocations_count,
            self.stats.symbols_count,
            self.stats.debug_bytes,
            self.sections.len(),
        )
    }
}

// ============================================================================
// Public API Factory Functions
// ============================================================================

/// Create an X86 code emission preparer for x86-64 targets.
pub fn make_x86_64_code_emission(target: &str) -> X86CodeEmission {
    X86CodeEmission::new_x86_64(target)
}

/// Create an X86 code emission preparer for x86-32 targets.
pub fn make_x86_32_code_emission(target: &str) -> X86CodeEmission {
    X86CodeEmission::new_x86_32(target)
}

/// Create a code emission preparer with all features enabled.
pub fn make_code_emission_full(target: &str) -> X86CodeEmission {
    let config = CodeEmissionConfig {
        emit_debug_line: true,
        emit_cfi: true,
        emit_eh_tables: true,
        optimize_alignments: true,
        ..CodeEmissionConfig::default()
    };
    X86CodeEmission::new_x86_64(target).with_config(config)
}

/// Create a code emission preparer for release (no debug info).
pub fn make_code_emission_release(target: &str) -> X86CodeEmission {
    let config = CodeEmissionConfig {
        emit_debug_line: false,
        emit_cfi: false,
        emit_eh_tables: false,
        optimize_alignments: true,
        ..CodeEmissionConfig::default()
    };
    X86CodeEmission::new_x86_64(target).with_config(config)
}

/// Run full code emission preparation on a function.
pub fn prepare_for_emission(mf: &MachineFunction, target: &str) -> X86CodeEmission {
    let mut emitter = make_x86_64_code_emission(target);
    emitter.prepare_function(mf);
    emitter
}

// ============================================================================
// Tests
// ============================================================================

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_encode_uleb128_zero() {
        let encoded = encode_uleb128(0);
        assert_eq!(encoded, vec![0x00]);
    }

    #[test]
    fn test_encode_uleb128_small() {
        let encoded = encode_uleb128(127);
        assert_eq!(encoded, vec![0x7F]);
    }

    #[test]
    fn test_encode_uleb128_large() {
        let encoded = encode_uleb128(128);
        assert_eq!(encoded, vec![0x80, 0x01]);
    }

    #[test]
    fn test_encode_uleb128_very_large() {
        let encoded = encode_uleb128(624485);
        // 624485 = 0x98765 = encoded as 0xE5 0x8E 0x26
        assert_eq!(encoded, vec![0xE5, 0x8E, 0x26]);
    }

    #[test]
    fn test_encode_sleb128_zero() {
        let encoded = encode_sleb128(0);
        assert_eq!(encoded, vec![0x00]);
    }

    #[test]
    fn test_encode_sleb128_positive() {
        let encoded = encode_sleb128(64);
        assert_eq!(encoded, vec![0x40]);
    }

    #[test]
    fn test_encode_sleb128_negative() {
        let encoded = encode_sleb128(-1);
        assert_eq!(encoded, vec![0x7F]);
    }

    #[test]
    fn test_encode_sleb128_neg_64() {
        let encoded = encode_sleb128(-64);
        assert_eq!(encoded, vec![0x40]); // 0x40 with sign extension
    }

    #[test]
    fn test_generate_nop_padding_lengths() {
        for len in 1..=20 {
            let nops = generate_nop_padding(len, NOPVariant::Intel);
            assert_eq!(nops.len(), len, "NOP padding for len={}", len);
        }
    }

    #[test]
    fn test_generate_nop_padding_single_byte() {
        let nops = generate_nop_padding(5, NOPVariant::SingleByte);
        assert_eq!(nops, vec![0x90, 0x90, 0x90, 0x90, 0x90]);
    }

    #[test]
    fn test_generate_alignment_padding() {
        // Current offset: 3, alignment: 4, should add 1 byte.
        let padding = generate_alignment_padding(3, 4, NOPVariant::Intel);
        assert_eq!(padding.len(), 1);

        // Current offset: 4, alignment: 4, should add 0 bytes.
        let padding = generate_alignment_padding(4, 4, NOPVariant::Intel);
        assert_eq!(padding.len(), 0);

        // Current offset: 5, alignment: 16, should add 11 bytes.
        let padding = generate_alignment_padding(5, 16, NOPVariant::Intel);
        assert_eq!(padding.len(), 11);
    }

    #[test]
    fn test_elf_section_flags_text() {
        let flags = ElfSectionFlags::text();
        assert!(flags.alloc);
        assert!(flags.execinstr);
        assert!(!flags.write);
    }

    #[test]
    fn test_elf_section_flags_data() {
        let flags = ElfSectionFlags::data();
        assert!(flags.alloc);
        assert!(flags.write);
        assert!(!flags.execinstr);
    }

    #[test]
    fn test_elf_section_flags_rodata() {
        let flags = ElfSectionFlags::rodata();
        assert!(flags.alloc);
        assert!(!flags.write);
        assert!(!flags.execinstr);
    }

    #[test]
    fn test_elf_section_append() {
        let mut section =
            ElfSection::new(".test", ElfSectionType::Progbits, ElfSectionFlags::rodata());
        section.append_u32(0xDEADBEEF);
        assert_eq!(section.size, 4);
        assert_eq!(&section.data, &[0xEF, 0xBE, 0xAD, 0xDE]);
    }

    #[test]
    fn test_elf_section_append_u16() {
        let mut section =
            ElfSection::new(".test", ElfSectionType::Progbits, ElfSectionFlags::rodata());
        section.append_u16(0x1234);
        assert_eq!(section.data, vec![0x34, 0x12]);
    }

    #[test]
    fn test_elf_symbol_new_function() {
        let sym = ElfSymbol::new_function("my_func", 0x1000, 0x42, 1);
        assert_eq!(sym.name, "my_func");
        assert_eq!(sym.value, 0x1000);
        assert_eq!(sym.size, 0x42);
        assert_eq!(sym.symbol_type, SymbolType::Func);
        assert_eq!(sym.binding, SymbolBinding::Global);
    }

    #[test]
    fn test_elf_symbol_as_undefined() {
        let sym = ElfSymbol::new_function("ext_func", 0, 0, 1).as_undefined();
        assert!(sym.is_undefined);
        assert_eq!(sym.section_index, 0);
    }

    #[test]
    fn test_relocation_type_values() {
        assert_eq!(X86RelocationType::Dir64.elf_value_x86_64(), 1);
        assert_eq!(X86RelocationType::PC32.elf_value_x86_64(), 2);
        assert_eq!(X86RelocationType::GotPcRel.elf_value_x86_64(), 9);
    }

    #[test]
    fn test_dwarf_line_program_special_opcode() {
        let mut program = DwarfLineProgram::new();
        // line_advance = 0, addr_advance = 0 should produce opcode_base.
        program.emit_special_opcode(0, 0);
        // For line_base=-5, line_range=14, adjusted_line = 0 - (-5) = 5
        // The formula is: (adjusted_line) + (line_range * addr_advance)
        // Wait, that doesn't seem right. Let's verify: DWARF5 spec:
        // opcode = (line_increment - line_base) + (line_range * op_index)
        // So: (0 - (-5)) + (14 * 0) = 5
        // special_opcode = opcode_base + 5 = 13 + 5 = 18
        assert_eq!(program.bytecode[0], 18);
    }

    #[test]
    fn test_lsda_new() {
        let lsda = Lsda::new();
        assert_eq!(lsda.landing_pad_base, 0);
        assert!(lsda.call_sites.is_empty());
        assert!(lsda.actions.is_empty());
    }

    #[test]
    fn test_lsda_encode_empty() {
        let lsda = Lsda::new();
        let encoded = lsda.encode();
        // LP base (1 byte) + ttype encoding (1 byte) + ttype offset (1 byte for zero) +
        // call site table length (1 byte for zero) = at least 4 bytes.
        assert!(encoded.len() >= 4);
    }

    #[test]
    fn test_code_emission_config_default() {
        let config = CodeEmissionConfig::default();
        assert_eq!(config.function_alignment, 16);
        assert!(config.optimize_alignments);
        assert!(!config.emit_debug_line);
    }

    #[test]
    fn test_code_emission_new() {
        let emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        assert!(emitter.is_64bit);
        assert_eq!(emitter.text_section, ".text");
        assert!(emitter.sections.is_empty());
    }

    #[test]
    fn test_section_switch_creates_section() {
        let mut emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        emitter.switch_to_section(".text");
        assert!(emitter.sections.contains_key(".text"));
        assert_eq!(emitter.current_section, Some(".text".to_string()));
    }

    #[test]
    fn test_section_switch_no_duplicate() {
        let mut emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        emitter.switch_to_section(".text");
        let count_before = emitter.sections.len();
        emitter.switch_to_section(".text");
        assert_eq!(emitter.sections.len(), count_before);
    }

    #[test]
    fn test_symbol_emission() {
        let mut emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        emitter.switch_to_section(".text");
        emitter.emit_symbol("test_func", 0x4000, 64);
        assert_eq!(emitter.symbols.len(), 1);
        assert_eq!(emitter.symbols[0].name, "test_func");
    }

    #[test]
    fn test_relocation_emission() {
        let mut emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        emitter.emit_relocation(10, X86RelocationType::PC32, "puts", -4);
        assert_eq!(emitter.relocations.len(), 1);
        assert_eq!(emitter.relocations[0].offset, 10);
    }

    #[test]
    fn test_constant_island_registration() {
        let mut emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        let island = ConstantIsland {
            id: 0,
            offset: 0,
            values: vec![ConstantIslandEntry {
                value: 0xDEADBEEF,
                size: 8,
                is_pc_rel: true,
                label: None,
            }],
            alignment: 8,
            is_inline: true,
            function_name: "test".to_string(),
        };
        emitter.add_constant_island(island);
        assert_eq!(emitter.constant_islands.len(), 1);
        assert_eq!(emitter.stats.constant_islands, 1);
    }

    #[test]
    fn test_jump_table_registration() {
        let mut emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        let table = JumpTable {
            id: 0,
            function_name: "test".to_string(),
            entries: vec!["L0".to_string(), "L1".to_string()],
            entry_size: 8,
            min_case: 0,
            max_case: 1,
            alignment: 8,
            pc_relative: true,
            offset: 0,
        };
        emitter.add_jump_table(table);
        assert_eq!(emitter.jump_tables.len(), 1);
    }

    #[test]
    fn test_nop_variant_enum() {
        assert_eq!(NOPVariant::Intel as u8, NOPVariant::Intel as u8);
        assert_ne!(NOPVariant::Intel as u8, NOPVariant::Amd as u8);
    }

    #[test]
    fn test_symbol_type_values() {
        assert_eq!(SymbolType::Func.elf_value(), 2);
        assert_eq!(SymbolType::Object.elf_value(), 1);
        assert_eq!(SymbolType::Notype.elf_value(), 0);
    }

    #[test]
    fn test_symbol_binding_values() {
        assert_eq!(SymbolBinding::Global.elf_value(), 1);
        assert_eq!(SymbolBinding::Local.elf_value(), 0);
        assert_eq!(SymbolBinding::Weak.elf_value(), 2);
    }

    #[test]
    fn test_section_type_values() {
        assert_eq!(ElfSectionType::Progbits.elf_value(), 1);
        assert_eq!(ElfSectionType::Nobits.elf_value(), 8);
    }

    #[test]
    fn test_target_os_detection() {
        let emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        assert_eq!(emitter.config.target_os, TargetOs::Linux);

        let emitter = X86CodeEmission::new_x86_64("x86_64-apple-darwin");
        assert_eq!(emitter.config.target_os, TargetOs::MacOS);

        let emitter = X86CodeEmission::new_x86_64("x86_64-pc-windows-msvc");
        assert_eq!(emitter.config.target_os, TargetOs::Windows);
    }

    #[test]
    fn test_report_format() {
        let emitter = X86CodeEmission::new_x86_64("x86_64-unknown-linux-gnu");
        let report = emitter.report();
        assert!(report.contains("CodeEmission:"));
        assert!(report.contains("funcs=0"));
    }

    #[test]
    fn test_leb128_roundtrip() {
        let test_values: Vec<u64> = vec![0, 1, 127, 128, 255, 65535, 1_000_000];
        for val in &test_values {
            let encoded = encode_uleb128(*val);
            // Decode back (simple decoder).
            let mut decoded: u64 = 0;
            let mut shift: u32 = 0;
            for &byte in &encoded {
                decoded |= ((byte & 0x7F) as u64) << shift;
                shift += 7;
                if byte & 0x80 == 0 {
                    break;
                }
            }
            assert_eq!(decoded, *val, "ULEB128 roundtrip for {}", val);
        }
    }
}