Re: [PATCH v3 11/16] scripts/oss-fuzz: Add general-fuzzer build script

[Darren Kenny]

Hi Alex,

On Sunday, 2020-09-20 at 22:25:01 -04, Alexander Bulekov wrote:
> This parses a yaml file containing general-fuzzer configs and builds a
> separate oss-fuzz wrapper binary for each one, changing some
> preprocessor macros for each configuration. To avoid dealing with
> escaping and stringifying, convert each string into a byte-array
> representation
>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> ---
>  scripts/oss-fuzz/build_general_fuzzers.py | 69 +++++++++++++++++++++++
>  1 file changed, 69 insertions(+)
>  create mode 100755 scripts/oss-fuzz/build_general_fuzzers.py
>
> diff --git a/scripts/oss-fuzz/build_general_fuzzers.py 
> b/scripts/oss-fuzz/build_general_fuzzers.py
> new file mode 100755
> index 0000000000..918f1143a5
> --- /dev/null
> +++ b/scripts/oss-fuzz/build_general_fuzzers.py
> @@ -0,0 +1,69 @@
> +#!/usr/bin/env python3
> +# -*- coding: utf-8 -*-
> +
> +"""
> +This script creates wrapper binaries that invoke the general-device-fuzzer 
> with
> +configurations specified in a yaml config file.
> +"""
> +import sys
> +import os
> +import yaml
> +import tempfile
> +
> +CC = ""
> +TEMPLATE_FILENAME = "target_template.c"
> +TEMPLATE_PATH = ""
> +
> +
> +def usage():
> +    print("Usage: CC=COMPILER {} CONFIG_PATH \
> +OUTPUT_PATH_PREFIX".format(sys.argv[0]))

The indentation of this seems off.

Python will concatenate 2 or more strings that appear one after the
other, so it might be cleaner to write them like:

    print("Usage: CC=COMPILER {} CONFIG_PATH "
          "OUTPUT_PATH_PREFIX".format(sys.argv[0]))

There is no need for the backslash at the end due to the use of the
braces '()' here.


> +    sys.exit(0)
> +
> +
> +def str_to_c_byte_array(s):
> +    """
> +    Convert strings to byte-arrays so we don't worry about formatting
> +    strings to play nicely with cc -DQEMU_FUZZARGS etc
> +    """
> +    return ','.join('0x{:02x}'.format(ord(x)) for x in s)
> +
> +
> +def compile_wrapper(cfg, path):
> +    os.system('$CC -DQEMU_FUZZ_ARGS="{fuzz_args}" \
> +               -DQEMU_FUZZ_OBJECTS="{fuzz_objs}" \
> +               {wrapper_template} -o {output_bin}'.format(
> +                   fuzz_args=str_to_c_byte_array(cfg["args"].replace("\n", " 
> ")),
> +                   
> fuzz_objs=str_to_c_byte_array(cfg["objects"].replace("\n", " ")),
> +                   wrapper_template=TEMPLATE_PATH,
> +                   output_bin=path))
> +

Similarly here, it might look better as:

    os.system('$CC -DQEMU_FUZZ_ARGS="{fuzz_args}" '
              '-DQEMU_FUZZ_OBJECTS="{fuzz_objs}" '
              '{wrapper_template} -o {output_bin}'.format(
                   fuzz_args=str_to_c_byte_array(cfg["args"].replace("\n", " 
")),
                   fuzz_objs=str_to_c_byte_array(cfg["objects"].replace("\n", " 
")),
                   wrapper_template=TEMPLATE_PATH,
                   output_bin=path))

> +
> +
> +def main():
> +    global CC
> +    global TEMPLATE_PATH
> +    global OUTPUT_BIN_NAME
> +
> +    if len(sys.argv) != 3:
> +        usage()
> +
> +    cfg_path = sys.argv[1]
> +    out_path = sys.argv[2]
> +
> +    CC = os.getenv("CC", default="cc")
> +    TEMPLATE_PATH = os.path.join(os.path.dirname(__file__), 
> TEMPLATE_FILENAME)
> +    if not os.path.exists(TEMPLATE_PATH):
> +        print("Error {} doesn't exist".format(TEMPLATE_PATH))
> +        sys.exit(1)
> +
> +    with open(cfg_path, "r") as f:
> +        configs = yaml.load(f)["configs"]

Just in case, the use of .get("config". []) might work better here.

But also check if yaml.load() could possibly throw an exception if the
file, despite existing isn't able to be parsed.

Thanks,

Darren.