On Mon, May 11, 2020 at 2:46 PM Nick Desaulniers
<ndesaulni...@google.com> wrote:
>
> On Mon, May 11, 2020 at 11:09 AM Brian Gerst <brge...@gmail.com> wrote:
> > This looks like the same issue that we just discussed for bitops.h.
> > Add the "b" operand size modifier to force it to use the 8-bit
> > register names (and probably also needs the "w" modifier in the 16-bit
> > case).
>
> While it does feel familiar, it is slightly different.
> https://godbolt.org/z/Rme4Zg
> That case was both compilers validating the inline asm, yet generating
> assembly that the assembler would choke on. This case is validation
> in the front end failing.
> long long ret;
> switch (sizeof(ret)) {
> case 1:
> asm ("movb $5, %0" : "=q" (ret));
> break;
> case 8:;
> }
So if the issue here is that the output variable type is long long,
what code is using a 64-bit percpu variable on a 32-bit kernel? Can
you give a specific file that fails to build with Clang? If Clang is
choking on it it may be silently miscompiling on GCC.
--
Brian Gerst
