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Avoid using ebx as an asm! operand (#1121)

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It is sometimes reserved by LLVM.
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Amanieu d'Antras 2021-04-16 13:20:00 +01:00 • committed by GitHub
parent 23f45cc955
commit 0073d6ace3
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1 changed files with 8 additions and 7 deletions
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15
library/stdarch/crates/core_arch/src/x86/cpuid.rs
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@ -56,12 +56,16 @@ pub unsafe fn __cpuid_count(leaf: u32, sub_leaf: u32) -> CpuidResult {
let ecx;
let edx;
// LLVM sometimes reserves `ebx` for its internal use, we so we need to use
// a scratch register for it instead.
#[cfg(target_arch = "x86")]
{
asm!(
"mov {0}, ebx",
"cpuid",
"xchg {0}, ebx",
lateout(reg) ebx,
inlateout("eax") leaf => eax,
lateout("ebx") ebx,
inlateout("ecx") sub_leaf => ecx,
lateout("edx") edx,
options(nostack, preserves_flags),
@ -69,15 +73,12 @@ pub unsafe fn __cpuid_count(leaf: u32, sub_leaf: u32) -> CpuidResult {
}
#[cfg(target_arch = "x86_64")]
{
// x86-64 uses `rbx` as the base register, so preserve it.
// This works around a bug in LLVM with ASAN enabled:
// https://bugs.llvm.org/show_bug.cgi?id=17907
asm!(
"mov rsi, rbx",
"mov {0:r}, rbx",
"cpuid",
"xchg rsi, rbx",
"xchg {0:r}, rbx",
lateout(reg) ebx,
inlateout("eax") leaf => eax,
lateout("esi") ebx,
inlateout("ecx") sub_leaf => ecx,
lateout("edx") edx,
options(nostack, preserves_flags),