From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NXcyL-0006GS-TN for qemu-devel@nongnu.org; Wed, 20 Jan 2010 10:59:58 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NXcyH-00067G-0h for qemu-devel@nongnu.org; Wed, 20 Jan 2010 10:59:57 -0500 Received: from [199.232.76.173] (port=48710 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NXcyG-000673-Rs for qemu-devel@nongnu.org; Wed, 20 Jan 2010 10:59:52 -0500 Received: from mail-yx0-f188.google.com ([209.85.210.188]:62946) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NXcyG-0000cN-G2 for qemu-devel@nongnu.org; Wed, 20 Jan 2010 10:59:52 -0500 Received: by yxe26 with SMTP id 26so4345340yxe.4 for ; Wed, 20 Jan 2010 07:59:52 -0800 (PST) Message-ID: <4B572876.8080800@codemonkey.ws> Date: Wed, 20 Jan 2010 09:59:50 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH 07/17] block/vvfat.c: fix warnings with _FORTIFY_SOURCE References: <85e877202ec86dac15d392f5e88d5b5d76e3b02f.1263944807.git.quintela@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Kirill A. Shutemov" Cc: qemu-devel@nongnu.org, Juan Quintela On 01/20/2010 12:19 AM, Kirill A. Shutemov wrote: > On Wed, Jan 20, 2010 at 1:56 AM, Juan Quintela wrote: > >> From: Kirill A. Shutemov >> >> CC block/vvfat.o >> cc1: warnings being treated as errors >> block/vvfat.c: In function 'commit_one_file': >> block/vvfat.c:2259: error: ignoring return value of 'ftruncate', declared with attribute warn_unused_result >> make: *** [block/vvfat.o] Error 1 >> CC block/vvfat.o >> In file included from /usr/include/stdio.h:912, >> from ./qemu-common.h:19, >> from block/vvfat.c:27: >> In function 'snprintf', >> inlined from 'init_directories' at block/vvfat.c:871, >> inlined from 'vvfat_open' at block/vvfat.c:1068: >> /usr/include/bits/stdio2.h:65: error: call to __builtin___snprintf_chk will always overflow destination buffer >> make: *** [block/vvfat.o] Error 1 >> >> Signed-off-by: Kirill A. Shutemov >> Signed-off-by: Juan Quintela >> --- >> block/vvfat.c | 9 +++++++-- >> 1 files changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/block/vvfat.c b/block/vvfat.c >> index 063f731..df957e5 100644 >> --- a/block/vvfat.c >> +++ b/block/vvfat.c >> @@ -868,7 +868,8 @@ static int init_directories(BDRVVVFATState* s, >> { >> direntry_t* entry=array_get_next(&(s->directory)); >> entry->attributes=0x28; /* archive | volume label */ >> - snprintf((char*)entry->name,11,"QEMU VVFAT"); >> + memcpy(entry->name,"QEMU VVF",8); >> + memcpy(entry->extension,"AT ",3); >> } >> > Better to use > > memcpy(entry->name, "QEMU VVFAT", 11); > > memcpy() doesn't check bounds. > Relying on such things is bad form because it isn't obvious to a casual reader what is happening. You have to know that entry->name is 8 chars long and realize that it will overflow into extension. Since that info is all the way in the structure definition, the result is difficult to read code. Any other discussions about whether the standards allow such a thing or whether tools are "stupid" is irrelevant. It's a neat trick but it results in more difficult to maintain code. Regards, Anthony Liguori