From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934962AbcJQPTH (ORCPT ); Mon, 17 Oct 2016 11:19:07 -0400 Received: from mail-wm0-f53.google.com ([74.125.82.53]:36236 "EHLO mail-wm0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934921AbcJQPS5 (ORCPT ); Mon, 17 Oct 2016 11:18:57 -0400 From: Michal Nazarewicz To: Ian Abbott , linux-kernel@vger.kernel.org Cc: Ian Abbott , Andrew Morton , Hidehiro Kawai , Borislav Petkov , Rasmus Villemoes , Johannes Berg , Peter Zijlstra , Alexander Potapenko Subject: Re: [PATCH] kernel.h: handle pointers to arrays better in container_of() In-Reply-To: <20161010201602.19412-1-abbotti@mev.co.uk> Organization: http://mina86.com/ References: <20161010201602.19412-1-abbotti@mev.co.uk> User-Agent: Notmuch/0.19+53~g2e63a09 (http://notmuchmail.org) Emacs/25.1.50.2 (x86_64-unknown-linux-gnu) Face: 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 X-Face: -TR8(rDTHy/(xl?SfWd1|3:TTgDIatE^t'vop%*gVg[kn$t{EpK(P"VQ=~T2#ysNmJKN$"yTRLB4YQs$4{[.]Fc1)*O]3+XO^oXM>Q#b^ix,O)Zbn)q[y06$`e3?C)`CwR9y5riE=fv^X@x$y?D:XO6L&x4f-}}I4=VRNwiA^t1-ZrVK^07.Pi/57c_du'& X-PGP: 50751FF4 X-PGP-FP: AC1F 5F5C D418 88F8 CC84 5858 2060 4012 5075 1FF4 X-Hashcash: 1:20:161017:glider@google.com::l+sAzz6wycjbJEAl:000000000000000000000000000000000000000000000UJt X-Hashcash: 1:20:161017:abbotti@mev.co.uk::7Vdc3iHrDc+9ZE1a:0000000000000000000000000000000000000000000002NT X-Hashcash: 1:20:161017:abbotti@mev.co.uk::sIzTJPmmKpset5C1:0000000000000000000000000000000000000000000008P2 X-Hashcash: 1:20:161017:hidehiro.kawai.ez@hitachi.com::B0lu9Mx2OTPbj5cp:000000000000000000000000000000001RZg X-Hashcash: 1:20:161017:akpm@linux-foundation.org::mfnocQ4RKgTfmVDH:0000000000000000000000000000000000002Fc4 X-Hashcash: 1:20:161017:bp@suse.de::jiRTg2AKFdhPIaVB:00000002NIP X-Hashcash: 1:20:161017:peterz@infradead.org::Oir4iQo4atN6iqYP:0000000000000000000000000000000000000000033aw X-Hashcash: 1:20:161017:johannes.berg@intel.com::noCmYKEfFMJfI6Gr:000000000000000000000000000000000000003rFx X-Hashcash: 1:20:161017:linux@rasmusvillemoes.dk::mXYA3a5Pc8gEtjiE:00000000000000000000000000000000000003ClE X-Hashcash: 1:20:161017:linux-kernel@vger.kernel.org::k6N0hIgmWSdIL/0w:0000000000000000000000000000000009jAD Date: Mon, 17 Oct 2016 17:18:54 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id u9HFJBrU003296 On Mon, Oct 10 2016, Ian Abbott wrote: > If the first parameter of container_of() is a pointer to a > non-const-qualified array type, the local variable __mptr will be > defined with a const-qualified array type. In ISO C, these types are > incompatible. They work as expected in GNU C, but some versions will > issue warnings. For example, GCC 4.9 produces the warning > "initialization from incompatible pointer type". Fix it by avoiding > defining the __mptr variable. This also avoids other GCC extensions. Alternatively, maybe even better, just drop ‘const’. Avoiding GCC extensions buys us anything especially since typeof is implemented by clang as well and likely many more compilers. > The container_of_safe() macro has the same problem. Here, we cannot > avoid all GCC extensions without eliminating possible side-effects, but > we can avoid having pointers to differently qualified array types. > > Signed-off-by: Ian Abbott > Cc: Andrew Morton > Cc: Michal Nazarewicz Acked-by: Michal Nazarewicz > Cc: Hidehiro Kawai > Cc: Borislav Petkov > Cc: Rasmus Villemoes > Cc: Johannes Berg > Cc: Peter Zijlstra > Cc: Alexander Potapenko > --- > include/linux/kernel.h | 11 +++++------ > 1 file changed, 5 insertions(+), 6 deletions(-) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index c64f998..5117b9f 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -832,9 +832,8 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } > * @member: the name of the member within the struct. > * > */ > -#define container_of(ptr, type, member) ({ \ > - const typeof( ((type *)0)->member ) *__mptr = (ptr); \ > - (type *)( (char *)__mptr - offsetof(type,member) );}) > +#define container_of(ptr, type, member) \ > + ((type *)((char *)(ptr) - offsetof(type, member))) > > /** > * container_of_safe - safe version of container_of > @@ -846,9 +845,9 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } > * @type, return 0. > */ > #define container_of_safe(ptr, type, member) ({ \ > - const typeof( ((type *)0)->member ) *__mptr = (ptr); \ > - (size_t)__mptr >= offsetof(type,member) ? \ > - (type *)( (char *)__mptr - offsetof(type,member) ) : (type *)0 ;}) > + char *__mptr = (char *)(ptr); \ > + (size_t)__mptr >= offsetof(type, member) ? \ > + (type *)(__mptr - offsetof(type, member)) : (type *)0; }) > > > /* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */ > -- > 2.9.3 > -- Best regards ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ «If at first you don’t succeed, give up skydiving»