Re: [PATCH 1/2] fuzz: add a script to build reproducers

[Darren Kenny]

Hi Alex,

On Saturday, 2021-03-13 at 23:23:56 -05, Alexander Bulekov wrote:
> Currently, bash and C crash reproducers are be built manually. This is a
> problem, as we want to integrate reproducers into the tree, for
> regression testing. This patch adds a script that converts a sequence of
> QTest commands into a pasteable Bash reproducer, or a libqtest-based C
> program. This will try to wrap pasteable reproducers to 72 chars, but
> the generated C code will not have nice formatting. Therefore, the C
> output of this script should be piped through an auto-formatter, such as
> clang-format
>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>

While I have a couple of comments (nits really) below, they are not
significant enough to require another review, so:

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

Thanks,

Darren.

> ---
>  scripts/oss-fuzz/output_reproducer.py | 160 ++++++++++++++++++++++++++
>  1 file changed, 160 insertions(+)
>  create mode 100755 scripts/oss-fuzz/output_reproducer.py
>
> diff --git a/scripts/oss-fuzz/output_reproducer.py 
> b/scripts/oss-fuzz/output_reproducer.py
> new file mode 100755
> index 0000000000..3608b0600e
> --- /dev/null
> +++ b/scripts/oss-fuzz/output_reproducer.py
> @@ -0,0 +1,160 @@
> +#!/usr/bin/env python3
> +# -*- coding: utf-8 -*-
> +
> +"""
> +Convert plain qtest traces to C or Bash reproducers
> +
> +Use this to help build bug-reports or create in-tree reproducers for bugs.
> +Note: This will not format C code for you. Pipe the output through
> +clang-format -style="{BasedOnStyle: llvm, IndentWidth: 4, ColumnLimit: 90}"
> +or similar
> +"""
> +
> +import sys
> +import os
> +import argparse
> +import textwrap
> +from datetime import date
> +
> +__author__     = "Alexander Bulekov <alxndr@bu.edu>"
> +__copyright__  = "Copyright (C) 2021, Red Hat, Inc."
> +__license__    = "GPL version 2 or (at your option) any later version"
> +
> +__maintainer__ = "Alexander Bulekov"
> +__email__      = "alxndr@bu.edu"
> +
> +
> +def c_header(owner):
> +    return """/*
> + * Autogenerated Fuzzer Test Case
> + *
> + * Copyright (c) {date} {owner}
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +
> +#include "libqos/libqtest.h"
> +
> +    """.format(date=date.today().year, owner=owner)

NIT: It might be cleaner, but not needed, to put the template strings ("""
     ... """) as global values in the code?

> +
> +def c_comment(s):
> +    """ Return a multi-line C comment. Assume the text is already wrapped """
> +    return "/*\n * " + "\n * ".join(s.splitlines()) + "\n*/"
> +
> +def print_c_function(s):
> +    print("/* ")
> +    for l in s.splitlines():
> +        print(" * {}".format(l))
> +
> +def bash_reproducer(path, args, trace):
> +    result = '\\\n'.join(textwrap.wrap("cat << EOF | {} {}".format(path, 
> args),
> +                                       72, break_on_hyphens=False,
> +                                       drop_whitespace=False))
> +    for l in trace.splitlines():
> +        result += "\n" + 
> '\\\n'.join(textwrap.wrap(l,72,drop_whitespace=False))
> +    result += "\nEOF"
> +    return result
> +
> +def c_reproducer(name, args, trace):
> +    result = []
> +    result.append("""static void {}(void)\n{{""".format(name))
> +
> +    # libqtest will add its own qtest args, so get rid of them
> +    args = args.replace("-accel qtest","")
> +    args = args.replace(",accel=qtest","")
> +    args = args.replace("-machine accel=qtest","")
> +    args = args.replace("-qtest stdio","")

NIT: Some of these might want to have an extra space removed either at
     the start of end, e.g. " -qtest stdio" or "-accel qtest ", to make
     the generated output a little cleaner.

> +    result.append("""QTestState *s = qtest_init("{}");""".format(args))
> +    for l in trace.splitlines():
> +        param = l.split()
> +        cmd = param[0]
> +        if cmd == "write":
> +            buf = param[3][2:] #Get the 0x... buffer and trim the "0x"
> +            assert len(buf)%2 == 0
> +            bufbytes = [buf[i:i+2] for i in range(0, len(buf), 2)]
> +            bufstring = '\\x'+'\\x'.join(bufbytes)
> +            addr = param[1]
> +            size = param[2]
> +            result.append("""qtest_bufwrite(s, {}, "{}", {});""".format(
> +                          addr, bufstring, size))
> +        elif cmd.startswith("in") or cmd.startswith("read"):
> +            result.append("qtest_{}(s, {});".format(
> +                          cmd, param[1]))
> +        elif cmd.startswith("out") or cmd.startswith("write"):
> +            result.append("qtest_{}(s, {}, {});".format(
> +                          cmd, param[1], param[2]))
> +        elif cmd == "clock_step":
> +            if len(param) ==1:
> +                result.append("qtest_clock_step_next(s);")
> +            else:
> +                result.append("qtest_clock_step(s, {});".format(param[1]))
> +    result.append("qtest_quit(s);\n}")
> +    return "\n".join(result)
> +
> +def c_main(name, arch):
> +    return """int main(int argc, char **argv)
> +{{
> +    const char *arch = qtest_get_arch();
> +
> +    g_test_init(&argc, &argv, NULL);
> +
> +   if (strcmp(arch, "{arch}") == 0) {{
> +        qtest_add_func("fuzz/{name}",{name});
> +   }}
> +
> +   return g_test_run();
> +}}""".format(name=name, arch=arch)

NIT: Same comment on the use of a template string.

> +
> +def main():
> +    parser = argparse.ArgumentParser()
> +    group = parser.add_mutually_exclusive_group()
> +    group.add_argument("-bash", help="Only output a copy-pastable bash 
> command",
> +                        action="store_true")
> +    group.add_argument("-c", help="Only output a c function",
> +                        action="store_true")
> +    parser.add_argument('-owner', help="If generating complete C source 
> code, \
> +                        this specifies the Copyright owner",
> +                        nargs='?', default="<name of author>")
> +    parser.add_argument("-no_comment", help="Don't include a bash reproducer 
> \
> +                        as a comment in the C reproducers",
> +                        action="store_true")
> +    parser.add_argument('-name', help="The name of the c function",
> +                        nargs='?', default="test_fuzz")
> +    parser.add_argument('input_trace', help="input QTest command sequence \
> +                        (stdin by default)",
> +                        nargs='?', type=argparse.FileType('r'),
> +                        default=sys.stdin)
> +    args = parser.parse_args()
> +
> +    qemu_path = os.getenv("QEMU_PATH")
> +    qemu_args = os.getenv("QEMU_ARGS")
> +    if not qemu_args or not qemu_path:
> +        print("Please set QEMU_PATH and QEMU_ARGS environment variables")
> +        sys.exit(1)
> +
> +    bash_args = qemu_args
> +    if " -qtest stdio" not in  qemu_args:
> +        bash_args += " -qtest stdio"
> +
> +    arch = qemu_path.split("-")[-1]
> +    trace = args.input_trace.read().strip()
> +
> +    if args.bash :
> +        print(bash_reproducer(qemu_path, bash_args, trace))
> +    else:
> +        output = ""
> +        if not args.c:
> +            output += c_header(args.owner) + "\n"
> +        if not args.no_comment:
> +            output += c_comment(bash_reproducer(qemu_path, bash_args, trace))
> +        output += c_reproducer(args.name, qemu_args, trace)
> +        if not args.c:
> +            output += c_main(args.name, arch)
> +        print(output)
> +
> +
> +if __name__ == '__main__':
> +    main()
> -- 
> 2.28.0