From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56954) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gZCOB-0001Sp-MB for qemu-devel@nongnu.org; Tue, 18 Dec 2018 05:14:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gZCO7-0002ri-FR for qemu-devel@nongnu.org; Tue, 18 Dec 2018 05:14:11 -0500 Received: from mail-wm1-f66.google.com ([209.85.128.66]:37746) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gZCO7-0002r6-7f for qemu-devel@nongnu.org; Tue, 18 Dec 2018 05:14:07 -0500 Received: by mail-wm1-f66.google.com with SMTP id g67so2140618wmd.2 for ; Tue, 18 Dec 2018 02:14:07 -0800 (PST) References: <20181217224807-mutt-send-email-mst@kernel.org> <20181217231145-mutt-send-email-mst@kernel.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Tue, 18 Dec 2018 11:14:04 +0100 MIME-Version: 1.0 In-Reply-To: <20181217231145-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] sheepdog build warning List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" , qemu-devel@nongnu.org Cc: Kevin Wolf , peter.maydell@linaro.org, qemu-block@nongnu.org, meyering@redhat.com, Jeff Cody , Liu Yuan , MORITA Kazutaka Hi Michael, On 12/18/18 5:16 AM, Michael S. Tsirkin wrote: > On Mon, Dec 17, 2018 at 11:03:11PM -0500, Michael S. Tsirkin wrote: >> mingw32 build on fedora fails with this warning: >> >> /scm/qemu/block/sheepdog.c: In function 'find_vdi_name': >> /scm/qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation] >> strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN); >> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> cc1: all warnings being treated as errors >> make: *** [/scm/qemu/rules.mak:69: block/sheepdog.o] Error 1 >> make: *** Waiting for unfinished jobs.... >> >> >> Reading the code one sees it's working as intended: >> >> >> static int find_vdi_name(BDRVSheepdogState *s, const char *filename, >> uint32_t snapid, const char *tag, uint32_t *vid, >> bool lock, Error **errp) >> { >> int ret, fd; >> SheepdogVdiReq hdr; >> SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr; >> unsigned int wlen, rlen = 0; >> char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN]; >> >> fd = connect_to_sdog(s, errp); >> if (fd < 0) { >> return fd; >> } >> >> /* This pair of strncpy calls ensures that the buffer is zero-filled, >> * which is desirable since we'll soon be sending those bytes, and >> * don't want the send_req to read uninitialized data. >> */ >> strncpy(buf, filename, SD_MAX_VDI_LEN); >> strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN); >> >> >> ..... >> >> } >> >> >> >> so this seems to be the case of GCC developers deciding that >> strncpy is simply a bad API and a correct use of it should be >> warned against. >> >> I propose either >> >> 1. simply adding >> >> #pragma GCC diagnostic ignored "-Wstringop-truncation" >> >> in osdep. >> >> 2. adding an inline wrapper with said pragma in there. >> >> 3. -Wno-stringop-truncation is the makefile >> >> Thoughts? >> >> -- > > > So here's approach 2. However I note that a newer gcc 8.2.1 > does not give this warning. Maybe detect at configure time > and suppress (option 3)? I prepared patches yesterday to fix this issue, I'll send to the list soon. I used another approach, replacing strncpy() by strpadcpy(pad=0). > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > index 3bf48bcdec..64d8258529 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -134,6 +134,22 @@ extern int daemon(int, int); > #define assert(x) g_assert(x) > #endif > > +/* > + * GCC 8.0 declared war on strncpy. Admittedly it's a tricky interface > + * with unintuitive semantics, but we use it widely. > + */ > +#if defined(__GNUC__) && __GNUC__ >= 8 > +static inline void qemu_strncpy(char *to, const char *from, int n) > +{ > +#pragma GCC diagnostic push > +#pragma GCC diagnostic ignored "-Wstringop-truncation" > + strncpy(to, from, n); > +#pragma GCC diagnostic pop > +} > + > +#define strncpy qemu_strncpy > +#endif > + > /* > * According to waitpid man page: > * WCOREDUMP >