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 = 0;

/// Dynamic linker runtime resolver for RISC-V 64-bit 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 floating-point
/// registers, calls the dynamic linker resolution function, and then restores
/// the state before jumping to the resolved function.
///
/// The function preserves all caller-saved integer registers (a0-a7, ra)
/// and optionally floating-point registers depending on the target features.
///
/// # 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!(
        "
        // 保存整数参数寄存器
        // 18 * 8 = 144 bytes, 保持 16 字节对齐
        addi sp,sp,-18*8
        sd ra,8*0(sp)
        sd a0,8*1(sp)
        sd a1,8*2(sp)
        sd a2,8*3(sp)
        sd a3,8*4(sp)
        sd a4,8*5(sp)
        sd a5,8*6(sp)
        sd a6,8*7(sp)
        sd a7,8*8(sp)
        ",
        #[cfg(target_feature = "d")]
        "
        fsd fa0,8*9(sp)
        fsd fa1,8*10(sp)
        fsd fa2,8*11(sp)
        fsd fa3,8*12(sp)
        fsd fa4,8*13(sp)
        fsd fa5,8*14(sp)
        fsd fa6,8*15(sp)
        fsd fa7,8*16(sp)
        ",
        #[cfg(all(target_feature = "f", not(target_feature = "d")))]
        "
        fsw fa0,8*9(sp)
        fsw fa1,8*10(sp)
        fsw fa2,8*11(sp)
        fsw fa3,8*12(sp)
        fsw fa4,8*13(sp)
        fsw fa5,8*14(sp)
        fsw fa6,8*15(sp)
        fsw fa7,8*16(sp)
        ",
        "
        // 这两个是plt代码设置的
        mv a0,t0
        srli a1,t1,3
        // 调用重定位函数
        call {0}
        // 恢复参数寄存器
        mv t1,a0
        ld ra,8*0(sp)
        ld a0,8*1(sp)
        ld a1,8*2(sp)
        ld a2,8*3(sp)
        ld a3,8*4(sp)
        ld a4,8*5(sp)
        ld a5,8*6(sp)
        ld a6,8*7(sp)
        ld a7,8*8(sp)
        ",
        #[cfg(target_feature = "d")]
        "
        fld fa0,8*9(sp)
        fld fa1,8*10(sp)
        fld fa2,8*11(sp)
        fld fa3,8*12(sp)
        fld fa4,8*13(sp)
        fld fa5,8*14(sp)
        fld fa6,8*15(sp)
        fld fa7,8*16(sp)
        ",
        #[cfg(all(target_feature = "f", not(target_feature = "d")))]
        "
        flw fa0,8*9(sp)
        flw fa1,8*10(sp)
        flw fa2,8*11(sp)
        flw fa3,8*12(sp)
        flw fa4,8*13(sp)
        flw fa5,8*14(sp)
        flw fa6,8*15(sp)
        flw fa7,8*16(sp)
        ",
        "
        addi sp,sp,18*8
        // 执行真正的函数
        jr t1
        ",
        sym crate::relocation::dl_fixup,
    )
}