AArch64 assembly compatibility for Xcode and GCC

["Andrew Fish" <afish@apple.com>]

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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


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