[PATCH v4 1/7] fuzz: accelerate non-crash detection

[Qiuhao Li <Qiuhao.Li@outlook.com>]

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 <Qiuhao.Li@outlook.com>
---
 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\
     < {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