relibc_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 = "mangled-names")))]
#[naked]
#[no_mangle]
pub unsafe 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" ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(all(windows, target_env = "gnu", not(feature = "mangled-names")))]
#[naked]
#[no_mangle]
pub unsafe 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"
         ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(all(windows, target_env = "gnu", not(feature = "mangled-names")))]
#[naked]
#[no_mangle]
pub unsafe 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"
        ::: "memory" : "volatile"
    );
    intrinsics::unreachable();
}