[lkml]   [2020]   [May]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v6 1/2] x86: fix bitops.h warning with a moved cast
On Mon, 4 May 2020 12:51:12 -0700
Nick Desaulniers <> 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

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:
> This is blowing up our KernelCI reports.

Bummer, how come none of those KernelCI reports are part of
zero-day testing at
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?

 \ /
  Last update: 2020-05-05 03:15    [W:0.127 / U:3.704 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site