elf_loader 0.15.0

A no_std-friendly ELF loader, runtime linker, and JIT linker for Rust.
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pub(crate) const DYLIB_OFFSET: usize = 1;
pub(crate) const RESOLVE_FUNCTION_OFFSET: usize = 2;

/// Dynamic linker runtime resolver for AArch64 PLT entries.
///
/// This function is called when a PLT entry needs to resolve a symbol address
/// at runtime. It saves the current register state including SIMD registers,
/// calls the dynamic linker resolution function, and then restores the state
/// before jumping to the resolved function.
///
/// The function preserves all caller-saved registers (x0-x8) and SIMD registers
/// (q0-q7) to ensure compatibility with the AArch64 calling convention.
///
/// # Safety
/// This function uses naked assembly and must be called with the correct
/// stack layout set up by the PLT stub code.
#[unsafe(naked)]
pub(crate) extern "C" fn dl_runtime_resolve() {
    core::arch::naked_asm!(
        "
    // ==========================================
    // 1. 保存上下文 (Context Save)
    // ==========================================
    // 需要保存:
    // - x0-x7 (整数参数)
    // - x8 (间接返回值地址，必须保存!)
    // - q0-q7 (浮点/向量参数，必须保存!)
    // 总计空间需求:
    // Q regs: 8 * 16 = 128 bytes
    // X regs: 9 * 8  = 72 bytes
    // Padding: 对齐到 16 字节 -> 总共需要 208 字节
    
    sub sp, sp, #208

    // 保存整数寄存器
    stp x0, x1, [sp, #0]
    stp x2, x3, [sp, #16]
    stp x4, x5, [sp, #32]
    stp x6, x7, [sp, #48]
    str x8,     [sp, #64]

    // 保存向量寄存器
    stp q0, q1, [sp, #80]
    stp q2, q3, [sp, #112]
    stp q4, q5, [sp, #144]
    stp q6, q7, [sp, #176]

    // ==========================================
    // 2. 准备 dl_fixup 参数
    // ==========================================
    // 目标: dl_fixup(struct link_map *l, ElfW(Word) reloc_index)
    
    // 【参数 1: link_map】
    // 标准 PLT0 保证 x16 指向 GOT[2]。
    // link_map 位于 GOT[1]，即 x16 - 8。
    ldr x0, [x16, #-8]

    // 【参数 2: reloc_index】
    // 计算公式: index = (&GOT[n] - &GOT[3]) / 8
    // - &GOT[n] 存储在 [sp + 208] (PLT0 压入的 x16)
    // - &GOT[3] 等于 x16 + 8 (因为 x16 是 GOT[2])
    
    ldr x10, [sp, #208]   // 从旧栈顶读取 &GOT[n]
    add x11, x16, #8      // 计算 &GOT[3] 的地址
    sub x1, x10, x11      // x1 = 字节偏移量
    lsr x1, x1, #3        // x1 = 偏移量 / 8 (得到索引)

    // 调用解析函数
    bl {dl_fixup}

    // x0 返回解析后的实际函数地址，暂存到 x17 (x17 是 caller-saved,可以随便用)
    mov x17, x0

    // ==========================================
    // 3. 恢复上下文 (Context Restore)
    // ==========================================
    ldp q0, q1, [sp, #80]
    ldp q2, q3, [sp, #112]
    ldp q4, q5, [sp, #144]
    ldp q6, q7, [sp, #176]

    ldp x0, x1, [sp, #0]
    ldp x2, x3, [sp, #16]
    ldp x4, x5, [sp, #32]
    ldp x6, x7, [sp, #48]
    ldr x8,     [sp, #64]

    // ==========================================
    // 4. 栈清理与跳转
    // ==========================================
    // 回收我们分配的 208 字节
    add sp, sp, #208

    // 弹出 PLT0 压入的 pair (x16, lr)
    // 注意：x16 (GOT entry) 已经没用了，但 LR (x30) 必须恢复
    ldp x16, x30, [sp], #16

    // 跳转到解析后的地址
    br x17
        ",
        dl_fixup = sym crate::relocation::dl_fixup,
    )
}