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x86/uaccess: Improve __try_cmpxchg64_user_asm() for x86_32

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Improve __try_cmpxcgh64_user_asm() for !CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT
by relaxing the output register constraint from "c" to "q" constraint,
which allows the compiler to choose between %ecx or %ebx register.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220628161612.7993-1-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2022-06-28 18:16:12 +02:00 committed by Borislav Petkov
parent 3163600cab
commit 4630535c64
1 changed files with 6 additions and 5 deletions
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11
arch/x86/include/asm/uaccess.h
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@ -448,7 +448,7 @@ do { \
#ifdef CONFIG_X86_32
/*
* Unlike the normal CMPXCHG, hardcode ECX for both success/fail and error.
* Unlike the normal CMPXCHG, use output GPR for both success/fail and error.
* There are only six GPRs available and four (EAX, EBX, ECX, and EDX) are
* hardcoded by CMPXCHG8B, leaving only ESI and EDI. If the compiler uses
* both ESI and EDI for the memory operand, compilation will fail if the error
@ -461,11 +461,12 @@ do { \
__typeof__(*(_ptr)) __new = (_new); \
asm volatile("\n" \
"1: " LOCK_PREFIX "cmpxchg8b %[ptr]\n" \
"mov $0, %%ecx\n\t" \
"setz %%cl\n" \
"mov $0, %[result]\n\t" \
"setz %b[result]\n" \
"2:\n" \
_ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG, %%ecx) \
: [result]"=c" (__result), \
_ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG, \
%[result]) \
: [result] "=q" (__result), \
"+A" (__old), \
[ptr] "+m" (*_ptr) \
: "b" ((u32)__new), \