ELF Assembler

A robust library for constructing and analyzing ELF (Executable and Linkable Format) binaries, tailored for Linux and Unix-like systems.

🏛️ Architecture

graph TB
    subgraph "ELF Construction Pipeline"
        A[Object Data] --> B[Section Header Table]
        B --> C[Program Header Table]
        C --> D[Relocation Resolver]
        D --> E[Symbol Table Generator]
        E --> F[ELF Binary]
        
        subgraph "Metadata Sections"
            G[.text / .data]
            H[.symtab / .strtab]
            I[.rela.text]
            J[.dynamic]
        end
        
        B --> G
        E --> H
        D --> I
        C --> J
    end

🚀 Features

Format Integrity

• Multi-Type Support: Generates Relocatable files (ET_REL), Executables (ET_EXEC), and Shared Objects (ET_DYN).
• Architecture Adaptation: Automatically configures ELF Class (32/64 bit), Endianness, and OS ABI metadata.
• Section Layout: Calculates section offsets and alignment, handling serialization of the .shstrtab section name table.

Core Capabilities

• Symbol & Relocation: Implements full symbol table mapping and relocation type processing (e.g., R_X86_64_PC32), supporting external symbol references.
• Dynamic Linking: Constructs .dynamic sections, configuring metadata required by dynamic loaders such as DT_NEEDED and DT_SONAME.
• Program Header Layout: Automatically generates PT_LOAD segments, managing read/write/execute permissions for memory segments.

Advanced Features

• Stripping: Supports optional symbol table stripping to reduce binary size.
• Zero-Copy Writing: Reduces I/O pressure by pre-allocating buffers when building large binaries.

💻 Usage

Generating a Simple ELF Executable

The following example demonstrates how to wrap raw x86_64 machine code into an ELF executable.

use elf_assembler::{types::ElfFile, writer::ElfWriter};
use std::{io::Cursor, fs};

fn main() {
    // 1. Prepare machine code (e.g., x86_64 exit(42))
    // mov rax, 60; mov rdi, 42; syscall
    let machine_code = vec![
        0xb8, 0x3c, 0x00, 0x00, 0x00, // mov eax, 60
        0xbf, 0x2a, 0x00, 0x00, 0x00, // mov edi, 42
        0x0f, 0x05                    // syscall
    ];

    // 2. Create ELF structure
    let elf = ElfFile::create_executable(machine_code);

    // 3. Write binary
    let mut buffer = Cursor::new(Vec::new());
    let mut writer = ElfWriter::new(&mut buffer);
    writer.write_elf_file(&elf).expect("Failed to write ELF");

    let binary = buffer.into_inner();
    fs::write("exit42", binary).expect("Failed to save file");
    
    println!("Generated ELF binary: ./exit42");
}

🛠️ Support Status

Legend: ✅ Supported, 🚧 In Progress, ❌ Not Supported

🔗 Relations

• gaia-types: Utilizes the BinaryReader and BinaryWriter for structured I/O of ELF headers and tables.
• gaia-assembler: Provides the ELF encapsulation layer for the assembler's Linux/Unix native backends.