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| author | Ingo Molnar <mingo@kernel.org> | 2020-11-27 11:09:57 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2020-11-27 11:10:50 +0100 |
| commit | a787bdaff83a085288b6fc607afb4bb648da3cc9 (patch) | |
| tree | ec389c1494ef4790ea90f65c4f86e523caf325d0 /include/linux/compiler.h | |
| parent | 2914b0ba61a9d253535e51af16c7122a8148995d (diff) | |
| parent | 85a2c56cb4454c73f56d3099d96942e7919b292f (diff) | |
| download | lwn-a787bdaff83a085288b6fc607afb4bb648da3cc9.tar.gz lwn-a787bdaff83a085288b6fc607afb4bb648da3cc9.zip | |
Merge branch 'linus' into sched/core, to resolve semantic conflict
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/compiler.h')
| -rw-r--r-- | include/linux/compiler.h | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index e512f5505dad..b8fe0c23cfff 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -80,11 +80,25 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, /* Optimization barrier */ #ifndef barrier -# define barrier() __memory_barrier() +/* The "volatile" is due to gcc bugs */ +# define barrier() __asm__ __volatile__("": : :"memory") #endif #ifndef barrier_data -# define barrier_data(ptr) barrier() +/* + * This version is i.e. to prevent dead stores elimination on @ptr + * where gcc and llvm may behave differently when otherwise using + * normal barrier(): while gcc behavior gets along with a normal + * barrier(), llvm needs an explicit input variable to be assumed + * clobbered. The issue is as follows: while the inline asm might + * access any memory it wants, the compiler could have fit all of + * @ptr into memory registers instead, and since @ptr never escaped + * from that, it proved that the inline asm wasn't touching any of + * it. This version works well with both compilers, i.e. we're telling + * the compiler that the inline asm absolutely may see the contents + * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495 + */ +# define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory") #endif /* workaround for GCC PR82365 if needed */ |