linux-x86/1.55.0/src/stdlibs/vendor/compiler_builtins/src/x86_64.rs

#![allow(unused_imports)]

use core::intrinsics;

// NOTE These functions are implemented using assembly because they using a custom
// calling convention which can't be implemented using a normal Rust function

// NOTE These functions are never mangled as they are not tested against compiler-rt
// and mangling ___chkstk would break the `jmp ___chkstk` instruction in __alloca

#[cfg(all(
    windows,
    target_env = "gnu",
    not(feature = "no-asm"),
    not(feature = "mangled-names")
))]
#[naked]
#[no_mangle]
pub unsafe extern "C" fn ___chkstk_ms() {
    asm!(
        "push   %rcx",
        "push   %rax",
        "cmp    $0x1000,%rax",
        "lea    24(%rsp),%rcx",
        "jb     1f",
        "2:",
        "sub    $0x1000,%rcx",
        "test   %rcx,(%rcx)",
        "sub    $0x1000,%rax",
        "cmp    $0x1000,%rax",
        "ja     2b",
        "1:",
        "sub    %rax,%rcx",
        "test   %rcx,(%rcx)",
        "pop    %rax",
        "pop    %rcx",
        "ret",
        options(noreturn, att_syntax)
    );
}

#[cfg(all(
    windows,
    target_env = "gnu",
    not(feature = "no-asm"),
    not(feature = "mangled-names")
))]
#[naked]
#[no_mangle]
pub unsafe extern "C" fn __alloca() {
    asm!(
        "mov    %rcx,%rax", // x64 _alloca is a normal function with parameter in rcx
        "jmp    ___chkstk", // Jump to ___chkstk since fallthrough may be unreliable"
        options(noreturn, att_syntax)
    );
}

#[cfg(all(
    windows,
    target_env = "gnu",
    not(feature = "no-asm"),
    not(feature = "mangled-names")
))]
#[naked]
#[no_mangle]
pub unsafe extern "C" fn ___chkstk() {
    asm!(
        "push   %rcx",
        "cmp    $0x1000,%rax",
        "lea    16(%rsp),%rcx", // rsp before calling this routine -> rcx
        "jb     1f",
        "2:",
        "sub    $0x1000,%rcx",
        "test   %rcx,(%rcx)",
        "sub    $0x1000,%rax",
        "cmp    $0x1000,%rax",
        "ja     2b",
        "1:",
        "sub    %rax,%rcx",
        "test   %rcx,(%rcx)",
        "lea    8(%rsp),%rax",  // load pointer to the return address into rax
        "mov    %rcx,%rsp",     // install the new top of stack pointer into rsp
        "mov    -8(%rax),%rcx", // restore rcx
        "push   (%rax)",        // push return address onto the stack
        "sub    %rsp,%rax",     // restore the original value in rax
        "ret",
        options(noreturn, att_syntax)
    );
}

// HACK(https://github.com/rust-lang/rust/issues/62785): x86_64-unknown-uefi needs special LLVM
// support unless we emit the _fltused
#[no_mangle]
#[used]
#[cfg(target_os = "uefi")]
static _fltused: i32 = 0;