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Mon, 11 Jan 2021 02:20:10 +0000 X-IncomingTopHeaderMarker: OriginalChecksum:C9727927224C28FA719C3765427D4ED1E6969E85A9D4D67E312E38E75FA767C6; UpperCasedChecksum:4CF9120D2EE532488CDD05F23840A198376B235F00871CC7864724E49F3E2A4D; SizeAsReceived:8956; Count:47 Received: from SYCPR01MB3502.ausprd01.prod.outlook.com ([fe80::b5dd:6210:81a:7780]) by SYCPR01MB3502.ausprd01.prod.outlook.com ([fe80::b5dd:6210:81a:7780%5]) with mapi id 15.20.3742.012; Mon, 11 Jan 2021 02:20:09 +0000 Message-ID: Subject: Re: [PATCH v4 1/7] fuzz: accelerate non-crash detection From: Qiuhao Li To: Alexander Bulekov Date: Mon, 11 Jan 2021 10:19:57 +0800 In-Reply-To: <20210110160040.uqlohbzr3viqhyxy@mozz.bu.edu> References: <20210107041827.sztisz72urbhxflx@mozz.bu.edu> <20210110160040.uqlohbzr3viqhyxy@mozz.bu.edu> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.4-0ubuntu1 Content-Transfer-Encoding: 7bit X-TMN: [//PfCff5mSh/AuO73JTt40W979lsBeKy] X-ClientProxiedBy: BYAPR05CA0053.namprd05.prod.outlook.com (2603:10b6:a03:74::30) To SYCPR01MB3502.ausprd01.prod.outlook.com (2603:10c6:10:3e::12) X-Microsoft-Original-Message-ID: MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from localhost (104.225.148.19) by BYAPR05CA0053.namprd05.prod.outlook.com (2603:10b6:a03:74::30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3763.2 via Frontend Transport; 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envelope-from=Qiuhao.Li@outlook.com; helo=APC01-HK2-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham 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: thuth@redhat.com, qemu-devel@nongnu.org, darren.kenny@oracle.com, bsd@redhat.com, stefanha@redhat.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sun, 2021-01-10 at 11:00 -0500, Alexander Bulekov wrote: > On 210110 2110, Qiuhao Li wrote: > > On Wed, 2021-01-06 at 23:18 -0500, Alexander Bulekov wrote: > > > On 201229 1240, Qiuhao Li wrote: > > > > We spend much time waiting for the timeout program during the > > > > minimization > > > > process until it passes a time limit. This patch hacks the > > > > CLOSED > > > > (indicates > > > > the redirection file closed) notification in QTest's output if > > > > it > > > > doesn't > > > > crash. > > > > > > > > Test with quadrupled trace input at: > > > > https://bugs.launchpad.net/qemu/+bug/1890333/comments/1 > > > > > > > > Original version: > > > > real 1m37.246s > > > > user 0m13.069s > > > > sys 0m8.399s > > > > > > > > Refined version: > > > > real 0m45.904s > > > > user 0m16.874s > > > > sys 0m10.042s > > > > > > > > Signed-off-by: Qiuhao Li > > > > --- > > > > scripts/oss-fuzz/minimize_qtest_trace.py | 41 > > > > ++++++++++++++++-- > > > > ------ > > > > 1 file changed, 28 insertions(+), 13 deletions(-) > > > > > > > > diff --git a/scripts/oss-fuzz/minimize_qtest_trace.py > > > > b/scripts/oss-fuzz/minimize_qtest_trace.py > > > > index 5e405a0d5f..aa69c7963e 100755 > > > > --- a/scripts/oss-fuzz/minimize_qtest_trace.py > > > > +++ b/scripts/oss-fuzz/minimize_qtest_trace.py > > > > @@ -29,30 +29,46 @@ whether the crash occred. Optionally, > > > > manually > > > > set a string that idenitifes the > > > > crash by setting CRASH_TOKEN= > > > > """.format((sys.argv[0]))) > > > > > > > > +deduplication_note = """\n\ > > > > +Note: While trimming the input, sometimes the mutated trace > > > > triggers a different > > > > +crash output but indicates the same bug. Under this situation, > > > > our > > > > minimizer is > > > > +incapable of recognizing and stopped from removing it. In the > > > > future, we may > > > > +use a more sophisticated crash case deduplication method. > > > > +\n""" > > > > + > > > > def check_if_trace_crashes(trace, path): > > > > - global CRASH_TOKEN > > > > with open(path, "w") as tracefile: > > > > tracefile.write("".join(trace)) > > > > > > > > - rc = subprocess.Popen("timeout -s 9 {timeout}s {qemu_path} > > > > {qemu_args} 2>&1\ > > > > + proc = subprocess.Popen("timeout {timeout}s {qemu_path} > > > > {qemu_args} 2>&1\ > > > > > > Why remove the -s 9 here? I ran into a case where the minimizer > > > got > > > stuck on one iteration. Adding back "sigkill" to the timeout can > > > be a > > > safety net to catch those bad cases. > > > -Alex > > > > Hi Alex, > > > > After reviewed this patch again, I think this get-stuck bug may be > > caused by code: > > > > - return CRASH_TOKEN in output > > Hi, > Thanks for fixing this. Strangely, I was able to fix it by swapping > the b'' for a ' ' when I was stuck on a testcase a few days ago. > vvv > > + for line in iter(rc.stdout.readline, b''): > > + if "CLOSED" in line: > > + return False > > + if CRASH_TOKEN in line: > > + return True > > > > I think your proposed change essentially does the same? > -Alex Hi Alex, It looks like I misused the bytes type. Instead of b'', '' (the str type) should be used here: - for line in iter(rc.stdout.readline, b''): + for line in iter(rc.stdout.readline, ''): And you are right, if we use iter() with sentinel parameter '', it's does the same as: + if line == "": + return False But if we just fix the get-stuck bug here, we may fail the assert(check_if_trace_crashes(newtrace, outpath)) check after remove_lines() or clear_bits() since the same trace input may trigger a different output between runs. My solution is instead of using the whole second-to-last line as token, we only use the the first three words which indicate the type of crash: - CRASH_TOKEN = output.splitlines()[-2] + CRASH_TOKEN = " ".join(outs.splitlines()[-2].split()[0:3]) Example: "SUMMARY: AddressSanitizer: stack-overflow" And thus, we may a get a more trimmed input trace. > > > I assumed there are only two end cases in lines of stdout, but > > while we > > are trimming the trace input, the crash output (second-to-last > > line) > > may changes, in which case we will go through the output and fail > > to > > find "CLOSED" and CRASH_TOKEN, thus get stuck in the loop above. > > > > To fix this bug and get a more trimmed input trace, we can: > > > > Use the first three words of the second-to-last line instead of the > > whole string, which indicate the type of crash as the token. > > > > - CRASH_TOKEN = output.splitlines()[-2] > > + CRASH_TOKEN = " ".join(outs.splitlines()[-2].split()[0:3]) > > > > If we reach the end of a subprocess' output, return False. > > > > + if line == "": > > + return False > > > > I fix it in [PATCH v7 1/7] and give an example. Could you review > > again? > > Thanks :-) > > > > FYI, I mentioned this situation firstly in [PATCH 1/4], where I > > gave a > > more detailed example: > > > > https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg05888.html > > > > > > < {trace_path}".format(timeout=TIMEOUT, > > > > qemu_path=QEMU_PATH, > > > > qemu_args=QEMU_ARGS, > > > > trace_path=path), > > > > shell=True, > > > > stdin=subprocess.PIPE, > > > > - stdout=subprocess.PIPE) > > > > - stdo = rc.communicate()[0] > > > > - output = stdo.decode('unicode_escape') > > > > - if rc.returncode == 137: # Timed Out > > > > - return False > > > > - if len(output.splitlines()) < 2: > > > > - return False > > > > - > > > > + stdout=subprocess.PIPE, > > > > + encoding="utf-8") > > > > + global CRASH_TOKEN > > > > if CRASH_TOKEN is None: > > > > - CRASH_TOKEN = output.splitlines()[-2] > > > > + try: > > > > + outs, _ = proc.communicate(timeout=5) > > > > + CRASH_TOKEN = outs.splitlines()[-2] > > > > + except subprocess.TimeoutExpired: > > > > + print("subprocess.TimeoutExpired") > > > > + return False > > > > + print("Identifying Crashes by this string: > > > > {}".format(CRASH_TOKEN)) > > > > + global deduplication_note > > > > + print(deduplication_note) > > > > + return True > > > > > > > > - return CRASH_TOKEN in output > > > > + for line in iter(proc.stdout.readline, b''): > > > > + if "CLOSED" in line: > > > > + return False > > > > + if CRASH_TOKEN in line: > > > > + return True > > > > + > > > > + return False > > > > > > > > > > > > def minimize_trace(inpath, outpath): > > > > @@ -66,7 +82,6 @@ def minimize_trace(inpath, outpath): > > > > print("Crashed in {} seconds".format(end-start)) > > > > TIMEOUT = (end-start)*5 > > > > print("Setting the timeout for {} > > > > seconds".format(TIMEOUT)) > > > > - print("Identifying Crashes by this string: > > > > {}".format(CRASH_TOKEN)) > > > > > > > > i = 0 > > > > newtrace = trace[:] > > > > -- > > > > 2.25.1 > > > >