Mercurial > hg
view tests/test-fuzz-targets.t @ 42562:97ada9b8d51b stable 5.0.2
posix: always seek to EOF when opening a file in append mode
Python 3 already does this, so skip it there.
Consider the program:
#include <stdio.h>
int main() {
FILE *f = fopen("narf", "w");
fprintf(f, "narf\n");
fclose(f);
f = fopen("narf", "a");
printf("%ld\n", ftell(f));
fprintf(f, "troz\n");
printf("%ld\n", ftell(f));
return 0;
}
on macOS, FreeBSD, and Linux with glibc, this program prints
5
10
but on musl libc (Alpine Linux and probably others) this prints
0
10
By my reading of
https://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html
this is technically correct, specifically:
> Opening a file with append mode (a as the first character in the
> mode argument) shall cause all subsequent writes to the file to be
> forced to the then current end-of-file, regardless of intervening
> calls to fseek().
in other words, the file position doesn't really matter in append-mode
files, and we can't depend on it being at all meaningful unless we
perform a seek() before tell() after open(..., 'a'). Experimentally
after a .write() we can do a .tell() and it'll always be reasonable,
but I'm unclear from reading the specification if that's a smart thing
to rely on. This matches what we do on Windows and what Python 3 does
for free, so let's just be consistent. Thanks to Yuya for the idea.
author | Augie Fackler <augie@google.com> |
---|---|
date | Mon, 08 Jul 2019 13:12:20 -0400 |
parents | d9fc51f77cc5 |
children | 39cab871e880 |
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#require test-repo $ cd $TESTDIR/../contrib/fuzz which(1) could exit nonzero, but that's fine because we'll still end up without a valid executable, so we don't need to check $? here. $ if which gmake >/dev/null 2>&1; then > MAKE=gmake > else > MAKE=make > fi $ havefuzz() { > cat > $TESTTMP/dummy.cc <<EOF > #include <stdlib.h> > #include <stdint.h> > int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) { return 0; } > int main(int argc, char **argv) { > const char data[] = "asdf"; > return LLVMFuzzerTestOneInput((const uint8_t *)data, 4); > } > EOF > $CXX $TESTTMP/dummy.cc -o $TESTTMP/dummy \ > -fsanitize=fuzzer-no-link,address || return 1 > } #if clang-libfuzzer $ CXX=clang++ havefuzz || exit 80 $ $MAKE -s clean all #endif #if no-clang-libfuzzer clang-6.0 $ CXX=clang++-6.0 havefuzz || exit 80 $ $MAKE -s clean all CC=clang-6.0 CXX=clang++-6.0 #endif #if no-clang-libfuzzer no-clang-6.0 $ exit 80 #endif Just run the fuzzers for five seconds each to verify it works at all. $ ./bdiff -max_total_time 5 $ ./mpatch -max_total_time 5 $ ./xdiff -max_total_time 5