From c95f3432118c6b7a3bde63aa6eb95ccd163119eb Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Tue, 13 Oct 2015 10:52:14 +0200 Subject: [PATCH] tools include: Fix strict-aliasing rules breakage MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Jiri Olsa Cc: Adrian Hunter Cc: Andi Kleen Cc: Martin Liska Cc: Peter Zijlstra Cc: Rabin Vincent Cc: linux-next@vger.kernel.org Link: http://lkml.kernel.org/r/20151013085214.GB2705@krava.brq.redhat.com Signed-off-by: Arnaldo Carvalho de Melo --- 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 9098083869c8..fa7208a32d76 100644 --- a/tools/include/linux/compiler.h +++ b/tools/include/linux/compiler.h @@ -43,13 +43,29 @@ #include +/* + * 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); -- GitLab