Bumping for this to get reviewed+picked up. Fixes a regression I would prefer didn't ship in 5.7.
On Mon, May 11, 2020 at 11:52 AM Brian Gerst <[email protected]> wrote: > > On Fri, May 8, 2020 at 2:32 PM Nick Desaulniers <[email protected]> > wrote: > > > > 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\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' > > > > 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. > > > > Cc: Jesse Brandeburg <[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 > > Fixes: 1651e700664b4 ("x86: Fix bitops.h warning with a moved cast") > > Reported-by: Sedat Dilek <[email protected]> > > 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]> > > Reviewed-By: Brian Gerst <[email protected]> -- Thanks, ~Nick Desaulniers
