Re: [edk2-devel] AArch64 assembly compatibility for Xcode and GCC

["Akira Moroo" <retrage01@gmail.com>]

Hi,

I tried to add support AArch64 XCODE5 about three months ago, too. I had the same compatibility issue in the other code. I just ended up adding ugly #ifdef as a workaround [1]. I think there are other compatibility issues in the current EDK2 code base. I’m not sure if the GAS macro and Apple Clang Assembler are compatible, but the C standard guarantees C preprocessor macro compatibility.

[1] https://github.com/retrage/edk2/commit/89b166758b9f858373bb20eb8e006914f7f13373

Best regards,

Akira Moroo

> On Jan 6, 2022, at 8:31, Pedro Falcato <pedro.falcato@gmail.com> wrote:
> 
> Hi,
> 
> GNU Assembler and the clang assembler support more complex macros natively (using the .macro and.endm directives), without the need for the C preprocessor.
> This completely sidesteps the need for explicit ";" as the GAS macros respect newlines inside the macro.
> 
> See https://godbolt.org/z/6zzqoeKE4 for a very simple example.
> Of course, you can also pass arguments, see https://sourceware.org/binutils/docs/as/Macro.html for the full documentation.
> 
> Best regards,
> Pedro
> 
> On Wed, Jan 5, 2022 at 8:36 PM Andrew Fish via groups.io <afish=apple.com@groups.io> wrote:
> I was playing around with getting Xcode to compile AArch64 code and I hit an interesting compatibility issue. The assembler line continuation token for GCC (;) is a comment for the Xcode clang assembler. For Xcode clang you need to use %%. Yikes [1]
> 
> I was wondering if any one else has hit this in another project and if there was any cool workaround?
> 
> The only thing I can think of is the “big hammer” on both (well you only need one) ends. We could replace ; with a #define that matches the assembler. It looks like this issue mostly hits in Code that is using C pre-processor macros so we could refactor the code. I’m a little concerned that the C pre processor is getting used since the macro languages of the assembler might also have some compatibility issues?
> 
> Looking for ideas and opinions on the best way to fix this if we want to add Xcode as an ARM compiler in the future. 
> 
> 
> [1] https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/AArch64/SetJumpLongJump.S#L13
> 
> #define GPR_LAYOUT                         \
>         REG_PAIR (x19, x20,  0);           \
>         REG_PAIR (x21, x22, 16);           \
>         REG_PAIR (x23, x24, 32);           \
>         REG_PAIR (x25, x26, 48);           \
>         REG_PAIR (x27, x28, 64);           \
>         REG_PAIR (x29, x30, 80);/*FP, LR*/ \
>         REG_ONE  (x16,      96) /*IP0*/
> 
> I had to change it to:
> 
> #define GPR_LAYOUT                         \
>         REG_PAIR (x19, x20,  0)%%          \
>         REG_PAIR (x21, x22, 16)%%          \
>         REG_PAIR (x23, x24, 32)%%          \
>         REG_PAIR (x25, x26, 48)%%          \
>         REG_PAIR (x27, x28, 64)%%          \
>         REG_PAIR (x29, x30, 80)%%/*FP, LR*/ \
>         REG_ONE  (x16,      96) /*IP0*/
> 
> Thanks,
> 
> Andrew Fish
> 
> 
> 
> 
> 
> -- 
> Pedro Falcato
>