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SubjectRe: [PATCH 1/3] x86: verify_cpu: use 32-bit arithmetic
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On May 17, 2018 2:30:01 PM PDT, Alexey Dobriyan <adobriyan@gmail.com> wrote:
>32-bit instructions are 1 byte shorter than 16-bit instructions.
>
>Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
>---
>
> arch/x86/kernel/verify_cpu.S | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
>--- a/arch/x86/kernel/verify_cpu.S
>+++ b/arch/x86/kernel/verify_cpu.S
>@@ -56,14 +56,14 @@ ENTRY(verify_cpu)
> cmpl $0x1,%eax
> jb .Lverify_cpu_no_longmode # no cpuid 1
>
>- xor %di,%di
>+ xor %edi, %edi
> cmpl $0x68747541,%ebx # AuthenticAMD
> jnz .Lverify_cpu_noamd
> cmpl $0x69746e65,%edx
> jnz .Lverify_cpu_noamd
> cmpl $0x444d4163,%ecx
> jnz .Lverify_cpu_noamd
>- mov $1,%di # cpu is from AMD
>+ mov $1, %edi # cpu is from AMD
> jmp .Lverify_cpu_check
>
> .Lverify_cpu_noamd:
>@@ -122,13 +122,13 @@ ENTRY(verify_cpu)
> andl $SSE_MASK,%edx
> cmpl $SSE_MASK,%edx
> je .Lverify_cpu_sse_ok
>- test %di,%di
>+ test %edi, %edi
> jz .Lverify_cpu_no_longmode # only try to force SSE on AMD
> movl $MSR_K7_HWCR,%ecx
> rdmsr
> btr $15,%eax # enable SSE
> wrmsr
>- xor %di,%di # don't loop
>+ xor %edi, %edi # don't loop
> jmp .Lverify_cpu_sse_test # try again
>
> .Lverify_cpu_no_longmode:

Well, in 32/64-bit mode... this code is also assembled in 16-bit mode, and the 16-but code is more space sensitive.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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