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qemu/atomic: Drop special case for unsupported compiler 

Since commit efc6c070ac ("configure: Add a test for the
minimum compiler version") the minimum compiler version
required for GCC is 4.8, which has the GCC BZ#36793 bug fixed.

We can safely remove the special case introduced in commit
a281ebc11a ("virtio: add missing mb() on notification").

With clang 3.4, __ATOMIC_RELAXED is defined, so the chunk to
remove (which is x86-specific), isn't reached either.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20201210134752.780923-2-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Philippe Mathieu-Daudé 2020-12-10 17:47:40 +04:00 committed by Paolo Bonzini
parent 98199a654c
commit 6a4757fe51
1 changed files with 0 additions and 17 deletions
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17
include/qemu/atomic.h
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@ -241,23 +241,6 @@
#else /* __ATOMIC_RELAXED */
/*
* We use GCC builtin if it's available, as that can use mfence on
* 32-bit as well, e.g. if built with -march=pentium-m. However, on
* i386 the spec is buggy, and the implementation followed it until
* 4.3 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36793).
*/
#if defined(__i386__) || defined(__x86_64__)
#if !QEMU_GNUC_PREREQ(4, 4)
#if defined __x86_64__
#define smp_mb() ({ asm volatile("mfence" ::: "memory"); (void)0; })
#else
#define smp_mb() ({ asm volatile("lock; addl $0,0(%%esp) " ::: "memory"); (void)0; })
#endif
#endif
#endif
#ifdef __alpha__
#define smp_read_barrier_depends() asm volatile("mb":::"memory")
#endif