Hi Arnd,
On Tue, Nov 17, 2015 at 09:57:30AM +0100, Arnd Bergmann wrote:
On Monday 16 November 2015 19:05:05 Olof's autobuilder wrote:
Errors:
arm64.allmodconfig:arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:75:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:79:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:83:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:75:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:79:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:83:3: error: read-only variable '___p1' used as 'asm' output arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
The patch below seems to fix it. Please review/apply.
8<---- Subject: ARM64: make smp_load_acquire() work with const arguments
smp_load_acquire() uses typeof() to declare a local variable for temporarily storing the output of the memory access. This fails when the argument is constant, because the assembler complains about using a constant register as output:
arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
Do you know the usage in the kernel causing this warning?
This changes the implementation to use an 'unsigned long' for the temporary value and only cast it to the original type in the end.
Signed-off-by: Arnd Bergmann arnd@arndb.de
diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h index 624f9679f4b0..05fa329467f6 100644 --- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -64,7 +64,7 @@ do { \ #define smp_load_acquire(p) \ ({ \
- typeof(*p) ___p1; \
- unsigned long ___p1; \ compiletime_assert_atomic_type(*p); \ switch (sizeof(*p)) { \ case 1: \
@@ -84,7 +84,7 @@ do { \ : "=r" (___p1) : "Q" (*p) : "memory"); \ break; \ } \
- ___p1; \
- (typeof(*p))___p1; \
My worry about having the cast here is if somebody decides to smp_load_acquire from a packed 64-bit structure (e.g. some sort of lock), then we'll get a conversion to non-scalar type error from the compiler.
Will