From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: [PATCH 7/8] tools include: Fix strict-aliasing rules breakage Date: Tue, 13 Oct 2015 16:41:42 -0300 Message-ID: <1444765303-8257-8-git-send-email-acme@kernel.org> References: <1444765303-8257-1-git-send-email-acme@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1444765303-8257-1-git-send-email-acme@kernel.org> Sender: linux-kernel-owner@vger.kernel.org To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, Jiri Olsa , Jiri Olsa , Adrian Hunter , Andi Kleen , Martin Liska , Peter Zijlstra , Rabin Vincent , linux-next@vger.kernel.org, Arnaldo Carvalho de Melo List-Id: linux-next.vger.kernel.org =46rom: Jiri Olsa 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 =E2=80=98disasm__purge=E2=80=99: linux-next/tools/include/linux/compiler.h:66: error: dereferencing pointer =E2=80=98res.41=E2=80=99 does break strict-aliasing rules The reason is READ_ONCE/WRITE_ONCE code we took from kernel sources. T= hey 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=3D3. 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.c= om 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/compi= ler.h index 9098083869c8..fa7208a32d76 100644 --- a/tools/include/linux/compiler.h +++ b/tools/include/linux/compiler.h @@ -43,13 +43,29 @@ =20 #include =20 +/* + * 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=3D3 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, v= oid *res, int size) { switch (size) { - case 1: *(__u8 *)res =3D *(volatile __u8 *)p; break; - case 2: *(__u16 *)res =3D *(volatile __u16 *)p; break; - case 4: *(__u32 *)res =3D *(volatile __u32 *)p; break; - case 8: *(__u64 *)res =3D *(volatile __u64 *)p; break; + case 1: *(__u8_alias_t *) res =3D *(volatile __u8_alias_t *) p; bre= ak; + case 2: *(__u16_alias_t *) res =3D *(volatile __u16_alias_t *) p; bre= ak; + case 4: *(__u32_alias_t *) res =3D *(volatile __u32_alias_t *) p; bre= ak; + case 8: *(__u64_alias_t *) res =3D *(volatile __u64_alias_t *) p; bre= ak; 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 =3D *(__u8 *)res; break; - case 2: *(volatile __u16 *)p =3D *(__u16 *)res; break; - case 4: *(volatile __u32 *)p =3D *(__u32 *)res; break; - case 8: *(volatile __u64 *)p =3D *(__u64 *)res; break; + case 1: *(volatile __u8_alias_t *) p =3D *(__u8_alias_t *) res; bre= ak; + case 2: *(volatile __u16_alias_t *) p =3D *(__u16_alias_t *) res; bre= ak; + case 4: *(volatile __u32_alias_t *) p =3D *(__u32_alias_t *) res; bre= ak; + case 8: *(volatile __u64_alias_t *) p =3D *(__u64_alias_t *) res; bre= ak; default: barrier(); __builtin_memcpy((void *)p, (const void *)res, size); --=20 2.1.0