Re: next build: 235 warnings 3 failures (next/next-20151117)

Arnd Bergmann
2015-11-17T08:58:12Z

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

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; \
})

#define read_barrier_depends() do { } while(0)