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

[Alexander Bulekov]

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 <Qiuhao.Li@outlook.com>

This makes a huge difference, thanks! Maybe there is some edge-case
where the crash happens after "CLOSED" (e.g. a timer fires after the
last command), but I haven't found such an example among existing
reproducers.

Reviewed-by: Alexander Bulekov <alxndr@bu.edu>

> ---
>  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
>