linker-utils 0.9.0

use crate::elf::AllowedRange;
use crate::elf::RelocationKind;
use crate::elf::RelocationKindInfo;
use crate::elf::RelocationSize;
use crate::elf::Sign;
use crate::relaxation::RelocationModifier;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RelaxationKind {
    /// Transforms a mov instruction that would have loaded an address to not use the GOT. The
    /// transformation will look like `mov *x(%rip), reg` -> `lea x(%rip), reg`.
    MovIndirectToLea,

    /// Transforms a mov instruction that would have loaded an absolute value to not use the GOT.
    /// The transformation will look like `mov *x(%rip), reg` ->  `mov x, reg`.
    MovIndirectToAbsolute,

    /// Transforms a mov instruction that would have loaded an absolute value to not use the GOT.
    /// The transformation will look like `mov *x(%rip), reg` ->  `mov x, reg`.
    RexMovIndirectToAbsolute(u8),

    // Transforms an indirect add to an absolute add.
    RexAddIndirectToAbsolute(u8),

    // Transforms an indirect sub to an absolute sub.
    RexSubIndirectToAbsolute(u8),

    // Transforms an indirect cmp to an absolute cmp.
    RexCmpIndirectToAbsolute(u8),

    /// Transform a call instruction like `call *x(%rip)` -> `call x(%rip)`.
    CallIndirectToRelative,

    /// Transform a jump instruction like `jmp *x(%rip)` -> `jmp x(%rip)`.
    JmpIndirectToRelative,

    /// Leave the instruction alone. Used when we only want to change the kind of relocation used.
    NoOp,

    /// Transform general dynamic (GD) into local exec.
    TlsGdToLocalExec,

    /// As above, but for the large-model form of the instruction.
    TlsGdToLocalExecLarge,

    /// Transform local dynamic (LD) into local exec.
    TlsLdToLocalExec,

    /// Transform local dynamic (LD) into local exec when the subsequent instruction is an indirect
    /// call instruction.
    TlsLdToLocalExecNoPlt,

    /// Transform local dynamic (LD) into local exec with extra padding because the previous
    /// instruction was 64 bit.
    TlsLdToLocalExec64,

    /// Transform general dynamic (GD) into initial exec
    TlsGdToInitialExec,

    // Transform TLSDESC to local exec for a statically linked executables.
    TlsDescToLocalExec(u8),

    // Transform TLSDESC to initial exec.
    TlsDescToInitialExec,

    /// Convert a TLSDESC_CALL to a no-op.
    SkipTlsDescCall,
}

impl RelaxationKind {
    pub fn apply(self, section_bytes: &mut [u8], offset_in_section: &mut u64, addend: &mut i64) {
        let offset = *offset_in_section as usize;
        match self {
            RelaxationKind::MovIndirectToLea => {
                // Since the value is an address, we transform a PC-relative mov into a PC-relative
                // lea.
                section_bytes[offset - 2] = 0x8d;
            }
            RelaxationKind::MovIndirectToAbsolute => {
                // Turn a PC-relative mov into an absolute mov.
                section_bytes[offset - 2] = 0xc7;
                let mod_rm = &mut section_bytes[offset - 1];
                *mod_rm = (*mod_rm >> 3) & 0x7 | 0xc0;
                *addend = 0;
            }
            RelaxationKind::RexMovIndirectToAbsolute(inst_offset) => {
                // Turn a PC-relative mov into an absolute mov.
                let rex = section_bytes[offset - 3];
                if inst_offset == 3 {
                    section_bytes[offset - 3] = (rex & !4) | ((rex & 4) >> 2);
                } else if inst_offset == 4 {
                    section_bytes[offset - 3] = (rex & !0x44) | ((rex & 0x44) >> 2);
                }
                section_bytes[offset - 2] = 0xc7;
                let mod_rm = &mut section_bytes[offset - 1];
                *mod_rm = (*mod_rm >> 3) & 0x7 | 0xc0;
                *addend = 0;
            }
            RelaxationKind::RexAddIndirectToAbsolute(inst_offset) => {
                if inst_offset == 3 {
                    let rex = section_bytes[offset - 3];
                    section_bytes[offset - 3] = (rex & !4) | ((rex & 4) >> 2);
                } else if inst_offset == 4 {
                    let rex = section_bytes[offset - 3];
                    section_bytes[offset - 3] = (rex & !0x44) | ((rex & 0x44) >> 2);
                } else if inst_offset == 6 {
                    let l5 = &mut section_bytes[offset - 5];
                    if (*l5 & (1 << 7)) == 0 {
                        *l5 = (*l5 | (1 << 7)) & !(1 << 5);
                    }
                    if (*l5 & (1 << 4)) == 0 {
                        *l5 = *l5 | (1 << 4) | (1 << 3);
                    }
                }
                section_bytes[offset - 2] = 0x81;
                let mod_rm = &mut section_bytes[offset - 1];
                *mod_rm = (*mod_rm >> 3) & 0x7 | 0xc0;
                *addend = 0;
            }
            RelaxationKind::RexSubIndirectToAbsolute(inst_offset) => {
                // Turn a PC-relative sub into an absolute sub.
                let rex = section_bytes[offset - 3];
                if inst_offset == 3 {
                    section_bytes[offset - 3] = (rex & !4) | ((rex & 4) >> 2);
                } else if inst_offset == 4 {
                    section_bytes[offset - 3] = (rex & !0x44) | ((rex & 0x44) >> 2);
                }
                section_bytes[offset - 2] = 0x81;
                let mod_rm = &mut section_bytes[offset - 1];
                *mod_rm = (*mod_rm >> 3) & 0x7 | 0xe8;
                *addend = 0;
            }
            RelaxationKind::RexCmpIndirectToAbsolute(inst_offset) => {
                // Turn a PC-relative cmp into an absolute cmp.
                let rex = section_bytes[offset - 3];
                if inst_offset == 3 {
                    section_bytes[offset - 3] = (rex & !4) | ((rex & 4) >> 2);
                } else if inst_offset == 4 {
                    section_bytes[offset - 3] = (rex & !0x44) | ((rex & 0x44) >> 2);
                }
                section_bytes[offset - 2] = 0x81;
                let mod_rm = &mut section_bytes[offset - 1];
                *mod_rm = (*mod_rm >> 3) & 0x7 | 0xf8;
                *addend = 0;
            }
            RelaxationKind::CallIndirectToRelative => {
                section_bytes[offset - 2..offset].copy_from_slice(&[0x67, 0xe8]);
            }
            RelaxationKind::JmpIndirectToRelative => {
                section_bytes[offset - 2..offset + 4].copy_from_slice(&[0xe9, 0, 0, 0, 0, 0x90]);
                *offset_in_section -= 1; // Instruction is 1 byte shorter
            }
            RelaxationKind::TlsGdToLocalExec => {
                section_bytes[offset - 4..offset + 8].copy_from_slice(&[
                    0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0, // mov %fs:0,%rax
                    0x48, 0x8d, 0x80, // lea {offset}(%rax),%rax
                ]);
                *offset_in_section += 8;
                *addend = 0;
            }
            RelaxationKind::TlsGdToLocalExecLarge => {
                section_bytes[offset - 3..offset + 19].copy_from_slice(&[
                    0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0, // mov %fs:0,%rax
                    0x48, 0x8d, 0x80, 0, 0, 0, 0, // lea {offset}(%rax),%rax
                    0x66, 0x0f, 0x1f, 0x44, 0, 0, // nopw (%rax,%rax)
                ]);
                *offset_in_section += 9;
                *addend = 0;
            }
            RelaxationKind::TlsGdToInitialExec => {
                section_bytes[offset - 4..offset + 8].copy_from_slice(&[
                    // mov %fs:0,%rax
                    0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0, // add *x,%rax
                    0x48, 0x03, 0x05,
                ]);
                *offset_in_section += 8;
            }
            RelaxationKind::TlsLdToLocalExec => {
                section_bytes[offset - 3..offset + 9].copy_from_slice(&[
                    // mov %fs:0,%rax
                    0x66, 0x66, 0x66, 0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0,
                ]);
                *offset_in_section += 5;
            }
            RelaxationKind::TlsLdToLocalExecNoPlt => {
                section_bytes[offset - 3..offset + 10].copy_from_slice(&[
                    // mov %fs:0,%rax
                    0x66, 0x66, 0x66, 0x66, 0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0,
                ]);
                *offset_in_section += 5;
            }
            RelaxationKind::TlsLdToLocalExec64 => {
                section_bytes[offset - 3..offset + 19].copy_from_slice(&[
                    // nopw (%rax,%rax)
                    0x66, 0x66, 0x66, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0, 0, 0, 0, 0,
                    // mov %fs:0,%rax
                    0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0,
                ]);
                *offset_in_section += 15;
            }
            RelaxationKind::TlsDescToLocalExec(inst_offset) => {
                let rex = section_bytes[offset - 3];
                let modrm = section_bytes[offset - 1];

                // Extract REX.R (bit 2 of rex) and reg field (bits 3-5 of modrm)
                let rex_r = (rex >> 2) & 1;
                let reg = (modrm >> 3) & 0x7;

                let rex = if inst_offset == 3 {
                    if rex_r == 0 { 0x48 } else { 0x49 }
                } else if inst_offset == 4 {
                    if rex_r == 0 { 0x18 } else { 0x19 }
                } else {
                    return;
                };
                section_bytes[offset - 3..offset + 4].copy_from_slice(&[
                    // mov {offset},%{reg}
                    rex,
                    0xc7,
                    0xc0 | reg,
                    0,
                    0,
                    0,
                    0,
                ]);
                *addend = 0;
            }
            RelaxationKind::TlsDescToInitialExec => {
                let rex = section_bytes[offset - 3];
                let modrm = section_bytes[offset - 1];

                // Extract REX.R (bit 2 of rex) and reg field (bits 3-5 of modrm)
                let rex_r = (rex >> 2) & 1;
                let reg = (modrm >> 3) & 0x7;

                let rex = if rex_r == 0 { 0x48 } else { 0x4c };
                section_bytes[offset - 3..offset + 4].copy_from_slice(&[
                    // mov {GOT}(%rip),%{reg}
                    rex,
                    0x8b,
                    0x05 | reg << 3,
                    0,
                    0,
                    0,
                    0,
                ]);
            }
            RelaxationKind::SkipTlsDescCall => {
                section_bytes[offset..offset + 2].copy_from_slice(&[
                    // xchg %ax,%ax
                    0x66, 0x90,
                ]);
            }
            RelaxationKind::NoOp => {}
        }
    }

    #[must_use]
    pub fn next_modifier(&self) -> RelocationModifier {
        match self {
            RelaxationKind::TlsGdToInitialExec
            | RelaxationKind::TlsGdToLocalExec
            | RelaxationKind::TlsGdToLocalExecLarge
            | RelaxationKind::TlsLdToLocalExec
            | RelaxationKind::TlsLdToLocalExecNoPlt
            | RelaxationKind::TlsLdToLocalExec64 => RelocationModifier::SkipNextRelocation,
            RelaxationKind::MovIndirectToLea
            | RelaxationKind::MovIndirectToAbsolute
            | RelaxationKind::RexMovIndirectToAbsolute(_)
            | RelaxationKind::RexAddIndirectToAbsolute(_)
            | RelaxationKind::RexSubIndirectToAbsolute(_)
            | RelaxationKind::RexCmpIndirectToAbsolute(_)
            | RelaxationKind::CallIndirectToRelative
            | RelaxationKind::JmpIndirectToRelative
            | RelaxationKind::TlsDescToLocalExec(_)
            | RelaxationKind::TlsDescToInitialExec
            | RelaxationKind::NoOp
            | RelaxationKind::SkipTlsDescCall => RelocationModifier::Normal,
        }
    }
}

type RelocSizeAndRange = (RelocationSize, AllowedRange);

const RELOC_8_BYTE_UNSIGNED: RelocSizeAndRange = (
    RelocationSize::ByteSize(8),
    AllowedRange::from_byte_size(8, Sign::Unsigned),
);
const RELOC_8_BYTE_SIGNED: RelocSizeAndRange = (
    RelocationSize::ByteSize(8),
    AllowedRange::from_byte_size(8, Sign::Signed),
);
const RELOC_4_BYTE_UNSIGNED: RelocSizeAndRange = (
    RelocationSize::ByteSize(4),
    AllowedRange::from_byte_size(4, Sign::Unsigned),
);
const RELOC_4_BYTE_SIGNED: RelocSizeAndRange = (
    RelocationSize::ByteSize(4),
    AllowedRange::from_byte_size(4, Sign::Signed),
);
const RELOC_2_BYTE_SIGNED: RelocSizeAndRange = (
    RelocationSize::ByteSize(2),
    AllowedRange::from_byte_size(2, Sign::Signed),
);
const RELOC_1_BYTE_SIGNED: RelocSizeAndRange = (
    RelocationSize::ByteSize(1),
    AllowedRange::from_byte_size(1, Sign::Signed),
);
const RELOC_NONE: RelocSizeAndRange = (RelocationSize::ByteSize(0), AllowedRange::no_check());

/// Returns the supplied x86-64 relocation as RelocationKindType. Returns `None` if the r_type isn't
/// recognised.
#[must_use]
#[inline(always)]
pub const fn relocation_from_raw(r_type: u32) -> Option<RelocationKindInfo> {
    let (kind, (size, range)) = match r_type {
        object::elf::R_X86_64_64 => (RelocationKind::Absolute, RELOC_8_BYTE_UNSIGNED),
        object::elf::R_X86_64_PC32 => (RelocationKind::Relative, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_PC64 => (RelocationKind::Relative, RELOC_8_BYTE_SIGNED),
        object::elf::R_X86_64_GOT32 => (RelocationKind::GotRelGotBase, RELOC_4_BYTE_UNSIGNED),
        object::elf::R_X86_64_GOT64 => (RelocationKind::GotRelGotBase, RELOC_8_BYTE_UNSIGNED),
        object::elf::R_X86_64_GOTOFF64 => (RelocationKind::SymRelGotBase, RELOC_8_BYTE_SIGNED),
        object::elf::R_X86_64_PLT32 => (RelocationKind::PltRelative, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_PLTOFF64 => (RelocationKind::PltRelGotBase, RELOC_8_BYTE_SIGNED),
        object::elf::R_X86_64_GOTPCREL => (RelocationKind::GotRelative, RELOC_4_BYTE_SIGNED),

        // For now, we rely on GOTPC64 and GOTPC32 always referencing the symbol
        // _GLOBAL_OFFSET_TABLE_, which means that we can just treat these as normal relative
        // relocations and avoid any special processing when writing.
        object::elf::R_X86_64_GOTPC64 => (RelocationKind::Relative, RELOC_8_BYTE_SIGNED),
        object::elf::R_X86_64_GOTPC32 => (RelocationKind::Relative, RELOC_4_BYTE_SIGNED),

        object::elf::R_X86_64_32 => (RelocationKind::Absolute, RELOC_4_BYTE_UNSIGNED),
        object::elf::R_X86_64_32S => (RelocationKind::Absolute, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_16 => (RelocationKind::Absolute, RELOC_2_BYTE_SIGNED),
        object::elf::R_X86_64_PC16 => (RelocationKind::Relative, RELOC_2_BYTE_SIGNED),
        object::elf::R_X86_64_8 => (RelocationKind::Absolute, RELOC_1_BYTE_SIGNED),
        object::elf::R_X86_64_PC8 => (RelocationKind::Relative, RELOC_1_BYTE_SIGNED),
        object::elf::R_X86_64_TLSGD => (RelocationKind::TlsGd, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_TLSLD => (RelocationKind::TlsLd, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_DTPOFF32 => (RelocationKind::DtpOff, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_DTPOFF64 => (RelocationKind::DtpOff, RELOC_8_BYTE_SIGNED),
        object::elf::R_X86_64_GOTTPOFF
        | object::elf::R_X86_64_CODE_4_GOTTPOFF
        | object::elf::R_X86_64_CODE_5_GOTTPOFF
        | object::elf::R_X86_64_CODE_6_GOTTPOFF => (RelocationKind::GotTpOff, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_GOTPCRELX
        | object::elf::R_X86_64_REX_GOTPCRELX
        | object::elf::R_X86_64_CODE_4_GOTPCRELX
        | object::elf::R_X86_64_CODE_5_GOTPCRELX
        | object::elf::R_X86_64_CODE_6_GOTPCRELX => {
            (RelocationKind::GotRelative, RELOC_4_BYTE_SIGNED)
        }
        object::elf::R_X86_64_TPOFF32 => (RelocationKind::TpOff, RELOC_4_BYTE_SIGNED),
        object::elf::R_X86_64_GOTPC32_TLSDESC
        | object::elf::R_X86_64_CODE_4_GOTPC32_TLSDESC
        | object::elf::R_X86_64_CODE_5_GOTPC32_TLSDESC
        | object::elf::R_X86_64_CODE_6_GOTPC32_TLSDESC => {
            (RelocationKind::TlsDesc, RELOC_4_BYTE_SIGNED)
        }
        object::elf::R_X86_64_TLSDESC_CALL => (RelocationKind::TlsDescCall, RELOC_NONE),
        object::elf::R_X86_64_NONE => (RelocationKind::None, RELOC_NONE),
        _ => return None,
    };

    Some(RelocationKindInfo {
        kind,
        size,
        mask: None,
        range,
        alignment: 1,
        bias: 0,
        thunkable: false,
    })
}