diff options
author | Arnaldo Carvalho de Melo <acme@redhat.com> | 2015-07-05 17:12:42 (GMT) |
---|---|---|
committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2015-07-05 18:05:00 (GMT) |
commit | 728abda6a6654ee7f4e903dc921c6307065e1644 (patch) | |
tree | a4cba7310c2cfae2039229c354e5dff77216286d /tools | |
parent | b9df84fd7c05cc300d6d14f022b8a00773ebcf8c (diff) | |
download | linux-728abda6a6654ee7f4e903dc921c6307065e1644.tar.xz |
tools: Adopt {READ,WRITE_ONCE} from the kernel
We need it to build rbtree.c after this cset:
commit d72da4a4d973
Author: Peter Zijlstra <peterz@infradead.org>
Date: Wed May 27 11:09:36 2015 +0930
rbtree: Make lockless searches non-fatal
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-qlnzhezv5ddwst0w9fydju0y@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools')
-rw-r--r-- | tools/include/linux/compiler.h | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h index f0e7267..9098083 100644 --- a/tools/include/linux/compiler.h +++ b/tools/include/linux/compiler.h @@ -41,4 +41,62 @@ #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +#include <linux/types.h> + +static __always_inline void __read_once_size(const volatile void *p, void *res, int size) +{ + switch (size) { + case 1: *(__u8 *)res = *(volatile __u8 *)p; break; + case 2: *(__u16 *)res = *(volatile __u16 *)p; break; + case 4: *(__u32 *)res = *(volatile __u32 *)p; break; + case 8: *(__u64 *)res = *(volatile __u64 *)p; break; + default: + barrier(); + __builtin_memcpy((void *)res, (const void *)p, size); + barrier(); + } +} + +static __always_inline void __write_once_size(volatile void *p, void *res, int size) +{ + switch (size) { + case 1: *(volatile __u8 *)p = *(__u8 *)res; break; + case 2: *(volatile __u16 *)p = *(__u16 *)res; break; + case 4: *(volatile __u32 *)p = *(__u32 *)res; break; + case 8: *(volatile __u64 *)p = *(__u64 *)res; break; + default: + barrier(); + __builtin_memcpy((void *)p, (const void *)res, size); + barrier(); + } +} + +/* + * Prevent the compiler from merging or refetching reads or writes. The + * compiler is also forbidden from reordering successive instances of + * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the + * compiler is aware of some particular ordering. One way to make the + * compiler aware of ordering is to put the two invocations of READ_ONCE, + * WRITE_ONCE or ACCESS_ONCE() in different C statements. + * + * In contrast to ACCESS_ONCE these two macros will also work on aggregate + * data types like structs or unions. If the size of the accessed data + * type exceeds the word size of the machine (e.g., 32 bits or 64 bits) + * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a + * compile-time warning. + * + * Their two major use cases are: (1) Mediating communication between + * process-level code and irq/NMI handlers, all running on the same CPU, + * and (2) Ensuring that the compiler does not fold, spindle, or otherwise + * mutilate accesses that either do not require ordering or that interact + * with an explicit memory barrier or atomic instruction that provides the + * required ordering. + */ + +#define READ_ONCE(x) \ + ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) + +#define WRITE_ONCE(x, val) \ + ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) + #endif /* _TOOLS_LINUX_COMPILER_H */ |