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 <jesse.brandeb...@intel.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/961
Link: https://lore.kernel.org/lkml/20200504193524.ga221...@google.com/
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 <sedat.di...@gmail.com>
Reported-by: kernelci.org bot <b...@kernelci.org>
Suggested-by: Andy Shevchenko <andriy.shevche...@intel.com>
Suggested-by: Brian Gerst <brge...@gmail.com>
Suggested-by: H. Peter Anvin <h...@zytor.com>
Suggested-by: Ilie Halip <ilie.ha...@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulni...@google.com>
---
Changes V2 -> V3:
* use `%b` "x86 Operand Modifier" instead of bitwise op then cast.
* reword commit message.
* add Brian and HPA suggested by tags
* drop Nathan & Sedat Tested by/reviewed by tags (new patch is different
enough).
Changes V1 -> V2:
* change authorship/signed-off-by to Ilie
* add Nathan's Tested by/reviewed by
* update commit message slightly with info sent to HPA.
arch/x86/include/asm/bitops.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index b392571c1f1d..03e24286e4eb 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -52,9 +52,9 @@ static __always_inline void
arch_set_bit(long nr, volatile unsigned long *addr)
{
if (__builtin_constant_p(nr)) {
- asm volatile(LOCK_PREFIX "orb %1,%0"
+ asm volatile(LOCK_PREFIX "orb %b1,%0"
: CONST_MASK_ADDR(nr, addr)
- : "iq" (CONST_MASK(nr) & 0xff)
+ : "iq" (CONST_MASK(nr))
: "memory");
} else {
asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0"
@@ -72,9 +72,9 @@ static __always_inline void
arch_clear_bit(long nr, volatile unsigned long *addr)
{
if (__builtin_constant_p(nr)) {
- asm volatile(LOCK_PREFIX "andb %1,%0"
+ asm volatile(LOCK_PREFIX "andb %b1,%0"
: CONST_MASK_ADDR(nr, addr)
- : "iq" (CONST_MASK(nr) ^ 0xff));
+ : "iq" (~CONST_MASK(nr)));
} else {
asm volatile(LOCK_PREFIX __ASM_SIZE(btr) " %1,%0"
: : RLONG_ADDR(addr), "Ir" (nr) : "memory");
--
2.26.2.645.ge9eca65c58-goog
