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From: | Paolo Bonzini |
Subject: | [Qemu-devel] Re: [PATCH] Suppress warning: zero-length gnu_printf format string |
Date: | Thu, 14 Oct 2010 19:52:16 +0200 |
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On 10/14/2010 06:38 PM, Blue Swirl wrote:
On Thu, Oct 14, 2010 at 9:20 AM, Markus Armbruster<address@hidden> wrote:Blue Swirl<address@hidden> writes:On Wed, Oct 13, 2010 at 7:19 AM, Markus Armbruster<address@hidden> wrote:Blue Swirl<address@hidden> writes:On Mon, Oct 11, 2010 at 12:52 PM, Markus Armbruster<address@hidden> wrote:Warns about this line in check-qjson.c: QObject *obj = qobject_from_json(""); The obvious fix (add -Wno-format-zero-length to gcc_flags) doesn't work, because -Wall switches it on again. Fix by putting configured flags last.This would disable the flag globally. I'd rather disable the flag only for check-qjson.oIs this warning worth the hassle? What's the problem with empty format strings?Your fix solves this specific case, but it also degrades the gcc checks of the mainstream code (slightly). I think the test suite need not follow the level of checking that should be applied to mainstream, or at least the warnings there should not be fatal."Degrade" implies we miss something that's "wrong" enough to be worth avoiding. What's wrong with empty format strings?They generate useless calls to the formatting function, wasting performance (slightly). Since there are no calls currently, this is of course hypothetical.
It is even more hypothetical when empty-format printfs are optimized away by GCC:
$ gcc -x c - -O2 -S -o - #include <stdio.h> main() { printf (""); } .file "" .text .p2align 4,,15 .globl main .type main, @function main: .LFB11: .cfi_startproc rep ret .cfi_endprocand other attribute-printf-marked functions are probably not noop when the format argument is empty.
Paolo
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