x86: bitops: fix build regression

This is easily reproducible via CC=clang + CONFIG_STAGING=y +
CONFIG_VT6656=m.

It turns out that if your config tickles __builtin_constant_p via
differences in choices to inline or not, these statements produce
invalid assembly:

    $ cat foo.c
    long a(long b, long c) {
      asm("orb	%1, %0" : "+q"(c): "r"(b));
      return c;
    }
    $ gcc foo.c
    foo.c: Assembler messages:
    foo.c:2: Error: `%rax' not allowed with `orb'

Use the `%b` "x86 Operand Modifier" to instead force register allocation
to select a lower-8-bit GPR operand.

The "q" constraint only has meaning on -m32 otherwise is treated as
"r".  Not all GPRs have low-8-bit aliases for -m32.

Fixes: 1651e700664b4 ("x86: Fix bitops.h warning with a moved cast")
Reported-by: kernelci.org bot <[email protected]>
Suggested-by: Andy Shevchenko <[email protected]>
Suggested-by: Brian Gerst <[email protected]>
Suggested-by: H. Peter Anvin <[email protected]>
Suggested-by: Ilie Halip <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Tested-by: Sedat Dilek <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>	[build, clang-11]
Reviewed-by: Nathan Chancellor <[email protected]>
Reviewed-By: Brian Gerst <[email protected]>
Reviewed-by: Jesse Brandeburg <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Luc Van Oostenryck <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Daniel Axtens <[email protected]>
Cc: "Peter Zijlstra (Intel)" <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Link: https://github.com/ClangBuiltLinux/linux/issues/961
Link: https://lore.kernel.org/lkml/[email protected]/
Link: https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#x86Operandmodifiers
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions