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Thu, 17 Sep 2020 07:29:33 +0000 (UTC) Subject: Re: [PATCH] migration: Silence compiler warning in global_state_store_running() To: Paolo Bonzini , Juan Quintela , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org References: <20200916171913.148681-1-thuth@redhat.com> <93744d31-0f33-5bb1-fb76-42ca3a5fa401@redhat.com> From: Thomas Huth Message-ID: Date: Thu, 17 Sep 2020 09:29:32 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0.003 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=205.139.110.61; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/17 02:23:38 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -51 X-Spam_score: -5.2 X-Spam_bar: ----- X-Spam_report: (-5.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.999, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.062, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-trivial@nongnu.org, =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 17/09/2020 09.18, Paolo Bonzini wrote: > On 17/09/20 08:30, Thomas Huth wrote: >> On 16/09/2020 19.19, Thomas Huth wrote: >>> GCC 9.3.0 on Ubuntu complains: >>> >>> In file included from /usr/include/string.h:495, >>> from /home/travis/build/huth/qemu/include/qemu/osdep.h:87, >>> from ../migration/global_state.c:13: >>> In function ‘strncpy’, >>> inlined from ‘global_state_store_running’ at ../migration/global_state.c:47:5: >>> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ specified bound 100 equals destination size [-Werror=stringop-truncation] >>> 106 | return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest)); >>> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> >>> ... but we apparently really want to do the strncpy here. Silence the >>> warning with QEMU_NONSTRING. >>> >>> Signed-off-by: Thomas Huth >>> --- >>> migration/global_state.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/migration/global_state.c b/migration/global_state.c >>> index 25311479a4..f1355d7d97 100644 >>> --- a/migration/global_state.c >>> +++ b/migration/global_state.c >>> @@ -43,9 +43,9 @@ int global_state_store(void) >>> void global_state_store_running(void) >>> { >>> const char *state = RunState_str(RUN_STATE_RUNNING); >>> + QEMU_NONSTRING char *dest = (char *)global_state.runstate; >>> assert(strlen(state) < sizeof(global_state.runstate)); >>> - strncpy((char *)global_state.runstate, >>> - state, sizeof(global_state.runstate)); >>> + strncpy(dest, state, sizeof(global_state.runstate)); >>> } >> >> Darn, I was sending too fast here, sorry, but seems like this does *not* >> fix the issue with GCC 9.3: >> >> https://travis-ci.com/github/huth/qemu/jobs/385871010#L2930 >> >> ... so maybe we should simply switch to strpadcpy() instead? > > Yes, and probably do so everywhere that strncpy is used. I think the trick with QEMU_NONSTRING should work fine in all cases where we have a real array, see e.g. buf[] in find_vdi_name() in block/sheepdog.c. It just does not seem to work in case you have a char* pointer instead of an array... Thomas