[cfe-dev] jump in inline assembly

[Reid Kleckner via cfe-dev]

Clang has no equivalent for GCC asm goto. LLVM does not support jumping
between inline asm blobs inside the same function.

Implementing that support is covered by
https://llvm.org/bugs/show_bug.cgi?id=9295, which is unlikely to happen.

On Fri, Oct 28, 2016 at 2:57 PM, Pietro Braione via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> I have a C program with an inline assembly instruction similar to this:
>
> a = b;
> if (foo)
>   asm volatile (“jmp *%0” : : “r” (baz)) /* baz points somewhere after etc
> */
>
> etc:
> /* here a is used */
>
> When compiled with -O2 clang moves the initialization of a after the if
> statement and before the first statement of etc, and as consequence the
> program segfaults when foo == 1.  It’s clear that clang presumes that after
> the asm volatile instruction the execution will fall through the next
> statement. gcc allows to use the goto keyword after asm [volatile] to
> inform that an asm block may jump, but this seems not to work in clang.
> What is the clang equivalent of asm goto? My clang -v: Apple LLVM version
> 8.0.0 (clang-800.0.38).
>
> Best,
> Pietro Braione
>
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