https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114876
Bug ID: 114876
Summary: -fprintf-return-value mishandles %lc with a '\0'
argument.
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: collin.funk1 at gmail dot com
Target Milestone: ---
I noticed some test failures in some Gnulib test cases earlier [1].
I'm using Fedora 40's GCC 14.0 package.
$ uname -a
Linux fedora 6.8.7-300.fc40.x86_64 #1 SMP PREEMPT_DYNAMIC Wed Apr 17 19:21:08
UTC 2024 x86_64 GNU/Linux
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/14/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,m2,lto --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id
--with-gcc-major-version-only --enable-libstdcxx-backtrace
--with-libstdcxx-zoneinfo=/usr/share/zoneinfo --with-linker-hash-style=gnu
--enable-plugin --enable-initfini-array
--with-isl=/builddir/build/BUILD/gcc-14.0.1-20240411/obj-x86_64-redhat-linux/isl-install
--enable-offload-targets=nvptx-none,amdgcn-amdhsa --enable-offload-defaulted
--without-cuda-driver --enable-gnu-indirect-function --enable-cet
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
--with-build-config=bootstrap-lto --enable-link-serialization=1
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.0.1 20240411 (Red Hat 14.0.1-0) (GCC)
$ ldd --version
ldd (GNU libc) 2.39
Here is a test program:
===================================================
int
main (void)
{
char buffer[5000];
wint_t ch = (wint_t) '\0';
int result = sprintf (buffer, "%lc%lc%lc%lc", ch, ch, ch, ch);
printf ("%d\n", result);
return 0;
}
===================================================
I believe that this program should print 4. POSIX states "Upon successful
completion, the sprintf() function shall return the number of bytes written to
s, excluding the terminating null byte." So in total 5 '\0' characters written
to the buffer and 4 returned because the extra terminating one is excluded.
Here is some runs with different optimization settings:
# -O0 passes.
$ make
gcc -Wall -Wextra -g -O0 -o a.out main.c
./a.out
4
# -01 fails, likewise for -O2 and -O3.
$ make
gcc -Wall -Wextra -g -O1 -o a.out main.c
./a.out
0
# -O0 -fprintf-return-value passes.
$ make
gcc -Wall -Wextra -g -O0 -fprintf-return-value -o a.out main.c
./a.out
4
# -01 -fprintf-return-value fails.
$ make
gcc -Wall -Wextra -g -O1 -fprintf-return-value -o a.out main.c
./a.out
0
# -O1 -fno-printf-return-value passes, likewise for -O2 and -O3 with
-fno-printf-return-value.
$ make
gcc -Wall -Wextra -g -O1 -fno-printf-return-value -o a.out main.c
./a.out
4
I also built a barebones gcc-13.2 compiler from the tarball on the GNU FTP
server. It seems to behave in the same way.
$ gcc-13.2 -v
Using built-in specs.
COLLECT_GCC=gcc-13.2
COLLECT_LTO_WRAPPER=/home/collin/.local/libexec/gcc/x86_64-pc-linux-gnu/13.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --prefix=/home/collin/.local
--program-suffix=-13.2 --enable-languages=c,c++ --enable-threads=posix
--enable-linker-build-id --disable-multilib --disable-multiarch
--with-tune=generic --disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.0 (GCC)
I've never submitted a GCC bug, so please let me know if you need any more
information. Thanks!
[1] https://lists.gnu.org/archive/html/bug-gnulib/2024-04/msg00453.html
