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atomic.h: Work around gcc spurious "unused value" warning

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Some versions of gcc produce a spurious warning if the result of
__atomic_compare_echange_n() is not used and the type involved
is a signed 8 bit value:
  error: value computed is not used [-Werror=unused-value]
This has been seen on at least
 gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609

Work around this by using an explicit cast to void to indicate
that we don't care about the return value.

We don't currently use our atomic_cmpxchg() macro on any signed
8 bit types, but the upcoming support for the Arm v8.1-Atomics
will require it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
This commit is contained in:
Peter Maydell 2018-05-10 18:10:57 +01:00
parent debbdc0018
commit cd95fc28fb
1 changed files with 1 additions and 1 deletions
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include/qemu/atomic.h
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@ -187,7 +187,7 @@
/* Returns the eventual value, failed or not */ /* Returns the eventual value, failed or not */
#define atomic_cmpxchg__nocheck(ptr, old, new) ({ \ #define atomic_cmpxchg__nocheck(ptr, old, new) ({ \
typeof_strip_qual(*ptr) _old = (old); \ typeof_strip_qual(*ptr) _old = (old); \
__atomic_compare_exchange_n(ptr, &_old, new, false, \ (void)__atomic_compare_exchange_n(ptr, &_old, new, false, \
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \ __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
_old; \ _old; \
}) })