From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Hogan Subject: Re: [PATCH] compiler.h: don't use temporary variable in __compiletime_assert() Date: Mon, 12 May 2014 14:42:04 +0100 Message-ID: <5370CFAC.40705@imgtec.com> References: <1399530685-7749-1-git-send-email-johannes@sipsolutions.net> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mailapp01.imgtec.com ([195.59.15.196]:62697 "EHLO mailapp01.imgtec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758142AbaELN5o (ORCPT ); Mon, 12 May 2014 09:57:44 -0400 In-Reply-To: <1399530685-7749-1-git-send-email-johannes@sipsolutions.net> Sender: linux-next-owner@vger.kernel.org List-ID: To: Johannes Berg , Andrew Morton , linux-kernel@vger.kernel.org, Peter Zijlstra , Daniel Santos Cc: "Paul E. McKenney" , linux-next , linux-metag Hi, On 08/05/14 07:31, Johannes Berg wrote: > From: Johannes Berg >=20 > Usually, BUG_ON and friends aren't even evaluated in sparse, but > recently compiletime_assert_atomic_type() was added, and that now > results in a sparse warning every time it is used. >=20 > The reason turns out to be the temporary variable, after it sparse > no longer considers the value to be a constant, and results in a > warning and an error. The error is the more annoying part of this > as it suppresses any further warnings in the same file, hiding > other problems. >=20 > Since this is all about compile time and the condition should be > side-effect free to start with, there's no downside (apart maybe > from a slight compilation time penalty?) to just duplicating it, > leaving sparse able to evaluate it at check time, getting rid of > the warning and error. >=20 > Signed-off-by: Johannes Berg > --- > include/linux/compiler.h | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) >=20 > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > index 2472740d7ab2..38c0e00ddef8 100644 > --- a/include/linux/compiler.h > +++ b/include/linux/compiler.h > @@ -324,11 +324,10 @@ void ftrace_likely_update(struct ftrace_branch_= data *f, int val, int expect); > =20 > #define __compiletime_assert(condition, msg, prefix, suffix) \ > do { \ > - bool __cond =3D !(condition); \ > extern void prefix ## suffix(void) __compiletime_error(msg); \ > - if (__cond) \ > + if (!(condition)) \ > prefix ## suffix(); \ > - __compiletime_error_fallback(__cond); \ > + __compiletime_error_fallback(!(condition)); \ > } while (0) > =20 > #define _compiletime_assert(condition, msg, prefix, suffix) \ >=20 Unfortunately this breaks the build of today's linux-next for the Meta architecture (arch/metag), which happens to use a fairly old compiler (based on gcc 4.2.4) which I presume is the reason why. A bunch of compile time asserts fail, even in code which should be optimised out. E.g. here's one which I analysed: mm/gup.c: In function =91follow_page_mask=92: mm/gup.c:208: error: size of array =91type name=92 is negative Line 208 uses HPAGE_PMD_NR which expands to a HPAGE_PMD_SHIFT, which expands to a BUILD_BUG(). However that line is inside an if block conditioned on pmd_trans_huge(*pmd) which include/asm-generic/pgtable.h defines inline to return 0, so the whole block should already be being optimised out. I don't understand why your patch should break things, I suspect it's related to the sparse behaviour you're trying to work around, but can w= e please drop this patch until a more portable workaround can be found? I'm happy to test further patches with metag if it helps. =46ull "make ARCH=3Dmetag -k -s" output below. Cheers James mm/gup.c: In function =91follow_page_mask=92: mm/gup.c:208: error: size of array =91type name=92 is negative In file included from arch/metag/include/asm/fixmap.h:55, from arch/metag/mm/init.c:26: include/asm-generic/fixmap.h: In function =91fix_to_virt=92: include/asm-generic/fixmap.h:31: error: size of array =91type name=92 i= s negative scripts/Makefile.build:318: recipe for target 'arch/metag/mm/init.o' fa= iled make[1]: *** [arch/metag/mm/init.o] Error 1 make[1]: Target '__build' not remade because of errors. Makefile:878: recipe for target 'arch/metag/mm' failed make: *** [arch/metag/mm] Error 2 mm/memory.c: In function =91copy_pmd_range=92: mm/memory.c:965: error: size of array =91type name=92 is negative mm/memory.c: In function =91zap_pmd_range=92: mm/memory.c:1232: error: size of array =91type name=92 is negative scripts/Makefile.build:318: recipe for target 'mm/memory.o' failed make[1]: *** [mm/memory.o] Error 1 mm/mremap.c: In function =91move_page_tables=92: mm/mremap.c:197: error: size of array =91type name=92 is negative mm/mprotect.c: In function =91change_pmd_range=92: mm/mprotect.c:164: error: size of array =91type name=92 is negative mm/mprotect.c:171: error: size of array =91type name=92 is negative mm/mprotect.c:172: error: size of array =91type name=92 is negative scripts/Makefile.build:318: recipe for target 'mm/mremap.o' failed make[1]: *** [mm/mremap.o] Error 1 scripts/Makefile.build:318: recipe for target 'mm/mprotect.o' failed make[1]: *** [mm/mprotect.o] Error 1 fs/proc/task_mmu.c: In function =91smaps_pmd=92: fs/proc/task_mmu.c:502: error: size of array =91type name=92 is negativ= e fs/proc/task_mmu.c:504: error: size of array =91type name=92 is negativ= e scripts/Makefile.build:318: recipe for target 'mm/gup.o' failed make[1]: *** [mm/gup.o] Error 1 scripts/Makefile.build:318: recipe for target 'fs/proc/task_mmu.o' fail= ed make[2]: *** [fs/proc/task_mmu.o] Error 1 make[2]: Target '__build' not remade because of errors. scripts/Makefile.build:465: recipe for target 'fs/proc' failed make[1]: *** [fs/proc] Error 2 make[1]: Target '__build' not remade because of errors. Makefile:878: recipe for target 'fs' failed make: *** [fs] Error 2 mm/pgtable-generic.c: In function =91pmdp_clear_flush_young=92: mm/pgtable-generic.c:104: error: size of array =91type name=92 is negat= ive scripts/Makefile.build:318: recipe for target 'mm/pgtable-generic.o' fa= iled make[1]: *** [mm/pgtable-generic.o] Error 1 make[1]: Target '__build' not remade because of errors. Makefile:878: recipe for target 'mm' failed make: *** [mm] Error 2 In file included from arch/metag/include/asm/fixmap.h:55, from arch/metag/include/asm/highmem.h:7, from arch/metag/kernel/setup.c:37: include/asm-generic/fixmap.h: In function =91fix_to_virt=92: include/asm-generic/fixmap.h:31: error: size of array =91type name=92 i= s negative scripts/Makefile.build:318: recipe for target 'arch/metag/kernel/setup.= o' failed make[1]: *** [arch/metag/kernel/setup.o] Error 1 make[1]: Target '__build' not remade because of errors. Makefile:878: recipe for target 'arch/metag/kernel' failed make: *** [arch/metag/kernel] Error 2 make: Target '_all' not remade because of errors.