I agree eax is better (0 extended and small size)
Jordan, I could clean up the incorrect usage in other packages.:-)
Jeff
From: Andrew Fish [mailto:[email protected]]
Sent: Wednesday, October 22, 2014 2:55 PM
To: [email protected]
Cc: Fan, Jeff; Tian, Feng
Subject: Re: [edk2] [PATCH] MdeModulePkg DebugSupportDxe: Fix build error with
GNU assembler
On Oct 21, 2014, at 11:27 PM, Jordan Justen
<[email protected]<mailto:[email protected]>> wrote:
On Sun, Oct 19, 2014 at 7:09 PM, Fan, Jeff
<[email protected]<mailto:[email protected]>> wrote:
SourceLevelDebugPkg/DebugAgentLib x64 also used movw %es, %rax.
We need to fix it also.
And UefiCpuPkg/Library/CpuExceptionLib x64 used movl %es, %eax.
We could clean it to make a consistence in code base.
More than that, it appears that the MASM code does a mov rax, es too.
I'm not sure that mov ax, es is really much of an improvement, and I'm
not interested in cleaning all that code up. I'd just like
MdeModulePkg to build. :) Would one of you be interested in pursuing
this cleanup?
I'm also not sure, but it could be that the mov rax, es actually does
a zero extended move, so maybe the mov ax, es would be different.
Would that impact the code that looks at this value later?
Actually it looks like eax is the correct form for X64 code ...
On the MASM side for X64 https://defuse.ca/online-x86-assembler.htm
mov rax, es
mov eax ,es
mov ax, es
mov es, rax
mov es, eax
mov es, ax
0: 48 8c c0 mov rax,es
3: 8c c0 mov eax,es
5: 66 8c c0 mov ax,es
8: 48 8e c0 mov es,rax
b: 8e c0 mov es,eax
d: 8e c0 mov es,eax
ax generates 0x66 - operand-size override prefix
rax generates 0x48 - REX use 64-bit operand size.
Anyway, I think that my original patch makes the code more consistent
with the current other GNU asm and MASM code. So, maybe it is okay as
a small next step?
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