[cfe-dev] asm directive: symbolic label syntax

[Brian Cain via cfe-dev]

Does the behavior change if you declare "cont" as a global symbol?  Does
the symbol have to be "cont"?  Would ".Lcont" suffice?  Many targets treat
leading ".L" as implicitly local symbols.

On Sun, Oct 10, 2021 at 6:30 PM Alexander von Below via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Thanks a lot for your answer, and yes, I do:
>
> Working code (using numeric label):
> https://github.com/below/HelloSilicon/blob/main/Chapter%2009/uppertst4.c
> Non-working
> <https://github.com/below/HelloSilicon/blob/main/Chapter%2009/uppertst4.cNon-working>
> (original) code:
> https://github.com/below/HelloSilicon/blob/4c4b2911c43644adfd3b78aee093857444f28472/Chapter%209/uppertst4.c
>
> Compile using the makefile in the same folder, or using "clang -o
> uppertst4 uppertst4.c“
>
> On godbolt, running the original code through  armv8-a-clang 11.0.1 or
> trunk, everything seems to work fine. There is an unrelated warning, but no
> errors. The output shows both the loop and the cont labels:
> https://godbolt.org/z/xY5afcYdW
>
> Compiling the code with the symbolic cont label on an M1 using
> clang-1300.0.29.3 produces the errors:
>
> uppertst4.c:22:4: error: conditional branch requires assembler-local
> label. 'cont' is external.
>                 "BGT    cont\n"
>                  ^
> <inline asm>:4:1: note: instantiated into assembly here
> BGT     cont
> ^
> uppertst4.c:24:4: error: conditional branch requires assembler-local
> label. 'cont' is external.
>                 "BLT    cont\n"
>                  ^
> <inline asm>:6:1: note: instantiated into assembly here
> BLT     cont
> ^
> uppertst4.c:28:4: error: conditional branch requires assembler-local
> label. 'loop' is external.
>                 "B.NE   loop\n"
>                  ^
> <inline asm>:10:1: note: instantiated into assembly here
> B.NE    loop
> ^
>
> Notably, now for both loop and cont, while it is sufficient to replace
> cont with a numeric label.
>
> I would be glad to find out if I am doing it wrong, or if this is an issue
> in clang. And now my curiosity is raised why godbolt appears to differ from
> clang on macOS …
>
> Thanks again
>
> Alex
>
>
> > Am 11.10.2021 um 00:26 schrieb Joerg Sonnenberger via cfe-dev <
> cfe-dev at lists.llvm.org>:
> >
> > On Sun, Oct 10, 2021 at 12:27:28PM +0200, Alexander von Below via
> cfe-dev wrote:
> >> I have tried to adapt gnu as code for Apple Silicon, and I have found
> >> explanations for most differences. There is one issue I still have:
> >
> > Do you actually have a complete self-contained example? Try godbolt.org.
> >
> > Joerg
> > _______________________________________________
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>
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-- 
-Brian
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