From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20200508183230.229464-1-ndesaulniers@xxxxxxxxxx
Link: https://github.com/ClangBuiltLinux/linux/issues/961
Link: https://lore.kernel.org/lkml/20200504193524.GA221287@xxxxxxxxxx/
Link: https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#x86Operandmodifiers
Fixes: 1651e700664b4 ("x86: Fix bitops.h warning with a moved cast")
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Reported-by: kernelci.org bot <bot@xxxxxxxxxxxx>
Suggested-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
Suggested-by: Brian Gerst <brgerst@xxxxxxxxx>
Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx>
Suggested-by: Ilie Halip <ilie.halip@xxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Reviewed-By: Brian Gerst <brgerst@xxxxxxxxx>
Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx> [build, clang-11]
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Daniel Axtens <dja@xxxxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/bitops.h | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/bitops.h~x86-bitops-fix-build-regression
+++ a/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");
@@ -123,9 +123,9 @@ static __always_inline void
arch_change_bit(long nr, volatile unsigned long *addr)
{
if (__builtin_constant_p(nr)) {
- asm volatile(LOCK_PREFIX "xorb %1,%0"
+ asm volatile(LOCK_PREFIX "xorb %b1,%0"
: CONST_MASK_ADDR(nr, addr)
- : "iq" ((u8)CONST_MASK(nr)));
+ : "iq" (CONST_MASK(nr)));
} else {
asm volatile(LOCK_PREFIX __ASM_SIZE(btc) " %1,%0"
: : RLONG_ADDR(addr), "Ir" (nr) : "memory");
_
