Messages in this thread |  | | Date | Mon, 4 May 2020 18:14:43 -0700 | From | Jesse Brandeburg <> | Subject | Re: [PATCH v6 1/2] x86: fix bitops.h warning with a moved cast |
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On Mon, 4 May 2020 12:51:12 -0700 Nick Desaulniers <ndesaulniers@google.com> wrote:
> Sorry for the very late report. It turns out that if your config > tickles __builtin_constant_p just right, this now produces invalid > assembly: > > $ cat foo.c > long a(long b, long c) { > asm("orb\t%1, %0" : "+q"(c): "r"(b)); > return c; > } > $ gcc foo.c > foo.c: Assembler messages: > foo.c:2: Error: `%rax' not allowed with `orb' > > The "q" constraint only has meanting on -m32 otherwise is treated as > "r". > > Since we have the mask (& 0xff), can we drop the `b` suffix from the > instruction? Or is a revert more appropriate? Or maybe another way to > skin this cat?
Figures that such a small change can create problems :-( Sorry for the thrash!
The patches in the link below basically add back the cast, but I'm interested to see if any others can come up with a better fix that a) passes the above code generation test b) still keeps sparse happy c) passes the test module and the code inspection
If need be I'm OK with a revert of the original patch to fix the issue in the short term, but it seems to me there must be a way to satisfy both tools. We went through several iterations on the way to the final patch that we might be able to pluck something useful from.
> Link: https://github.com/ClangBuiltLinux/linux/issues/961 > This is blowing up our KernelCI reports.
ASIDE: Bummer, how come none of those KernelCI reports are part of zero-day testing at https://01.org/lkp/documentation/0-day-test-service I'm interested in your answer but don't want to pollute this thread, feel free to contact me directly for this one or start a new thread?
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