Commit-ID: c95f3432118c6b7a3bde63aa6eb95ccd163119eb Gitweb: http://git.kernel.org/tip/c95f3432118c6b7a3bde63aa6eb95ccd163119eb Author: Jiri Olsa <jo...@redhat.com> AuthorDate: Tue, 13 Oct 2015 10:52:14 +0200 Committer: Arnaldo Carvalho de Melo <a...@redhat.com> CommitDate: Tue, 13 Oct 2015 11:43:16 -0300
tools include: Fix strict-aliasing rules breakage Vinson reported build breakage with gcc 4.4 due to strict-aliasing. CC util/annotate.o cc1: warnings being treated as errors util/annotate.c: In function ‘disasm__purge’: linux-next/tools/include/linux/compiler.h:66: error: dereferencing pointer ‘res.41’ does break strict-aliasing rules The reason is READ_ONCE/WRITE_ONCE code we took from kernel sources. They intentionaly break aliasing rules. While this is ok for kernel because it's built with -fno-strict-aliasing, it breaks perf which is build with -Wstrict-aliasing=3. Using extra __may_alias__ type to allow aliasing in this case. Reported-and-tested-by: Vinson Lee <v...@twopensource.com> Signed-off-by: Jiri Olsa <jo...@kernel.org> Cc: Adrian Hunter <adrian.hun...@intel.com> Cc: Andi Kleen <a...@linux.intel.com> Cc: Martin Liska <mli...@suse.cz> Cc: Peter Zijlstra <a.p.zijls...@chello.nl> Cc: Rabin Vincent <ra...@rab.in> Cc: linux-n...@vger.kernel.org Link: http://lkml.kernel.org/r/20151013085214.gb2...@krava.brq.redhat.com Signed-off-by: Arnaldo Carvalho de Melo <a...@redhat.com> --- tools/include/linux/compiler.h | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h index 9098083..fa7208a 100644 --- a/tools/include/linux/compiler.h +++ b/tools/include/linux/compiler.h @@ -43,13 +43,29 @@ #include <linux/types.h> +/* + * Following functions are taken from kernel sources and + * break aliasing rules in their original form. + * + * While kernel is compiled with -fno-strict-aliasing, + * perf uses -Wstrict-aliasing=3 which makes build fail + * under gcc 4.4. + * + * Using extra __may_alias__ type to allow aliasing + * in this case. + */ +typedef __u8 __attribute__((__may_alias__)) __u8_alias_t; +typedef __u16 __attribute__((__may_alias__)) __u16_alias_t; +typedef __u32 __attribute__((__may_alias__)) __u32_alias_t; +typedef __u64 __attribute__((__may_alias__)) __u64_alias_t; + 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; + case 1: *(__u8_alias_t *) res = *(volatile __u8_alias_t *) p; break; + case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break; + case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break; + case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break; default: barrier(); __builtin_memcpy((void *)res, (const void *)p, size); @@ -60,10 +76,10 @@ static __always_inline void __read_once_size(const volatile void *p, void *res, 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; + case 1: *(volatile __u8_alias_t *) p = *(__u8_alias_t *) res; break; + case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break; + case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break; + case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break; default: barrier(); __builtin_memcpy((void *)p, (const void *)res, size); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
