From 037283cbc74739b72f36dfec827d120faa243406 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Thu, 6 Jul 2017 11:50:55 +0200 Subject: [PATCH 26/26] assert: Suppress pedantic warning caused by statement expression [BZ# 21242] On 07/05/2017 10:15 PM, Zack Weinberg wrote: > On Wed, Jul 5, 2017 at 11:51 AM, Florian Weimer wrote: >> On 07/05/2017 05:46 PM, Zack Weinberg wrote: >>> A problem occurs to me: expressions involving VLAs _are_ evaluated >>> inside sizeof. >> >> The type of the sizeof argument would still be int (due to the >> comparison against 0), so this doesn't actually occur. > > I rechecked what C99 says about sizeof and VLAs, and you're right - > the operand of sizeof is only evaluated when sizeof is _directly_ > applied to a VLA. So this is indeed safe, but I think this wrinkle > should be mentioned in the comment. Perhaps > > /* The first occurrence of EXPR is not evaluated due to the sizeof, > but will trigger any pedantic warnings masked by the __extension__ > for the second occurrence. The explicit comparison against zero > ensures that sizeof is not directly applied to a function pointer or > bit-field (which would be ill-formed) or VLA (which would be evaluated). */ > > zw What about the attached patch? Siddhesh, is this okay during the freeze? I'd like to backport it to 2.25 as well. Thanks, Florian assert: Suppress pedantic warning caused by statement expression 2017-07-06 Florian Weimer [BZ #21242] * assert/assert.h [__GNUC__ && !__STRICT_ANSI__] (assert): Suppress pedantic warning resulting from statement expression. (__ASSERT_FUNCTION): Add missing __extendsion__. --- Upstream-Status: Submitted Signed-off-by: Khem Raj assert/assert.h | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/assert/assert.h b/assert/assert.h index 22f019537c..6801cfeb10 100644 --- a/assert/assert.h +++ b/assert/assert.h @@ -91,13 +91,19 @@ __END_DECLS ? __ASSERT_VOID_CAST (0) \ : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION)) # else +/* The first occurrence of EXPR is not evaluated due to the sizeof, + but will trigger any pedantic warnings masked by the __extension__ + for the second occurrence. The explicit comparison against zero is + required to support function pointers and bit fields in this + context, and to suppress the evaluation of variable length + arrays. */ # define assert(expr) \ - ({ \ + ((void) sizeof ((expr) == 0), __extension__ ({ \ if (expr) \ ; /* empty */ \ else \ __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION); \ - }) + })) # endif # ifdef __USE_GNU @@ -113,7 +119,7 @@ __END_DECLS C9x has a similar variable called __func__, but prefer the GCC one since it demangles C++ function names. */ # if defined __cplusplus ? __GNUC_PREREQ (2, 6) : __GNUC_PREREQ (2, 4) -# define __ASSERT_FUNCTION __PRETTY_FUNCTION__ +# define __ASSERT_FUNCTION __extension__ __PRETTY_FUNCTION__ # else # if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L # define __ASSERT_FUNCTION __func__ -- 2.13.3