https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109673
Bug ID: 109673
Summary: warn_unused_result warnings are incorrect (and/or
missing) and vary when -Os is specified
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: parke.nexus at gmail dot com
Target Milestone: ---
When I compile the below sample program without -Os, I expect one warning but
receive zero warnings.
When I compile the below sample program with -Os, I expect one warning but
receive two warnings.
#include <unistd.h>
char s[80];
int main () {
; getcwd ( s, sizeof s ); // I expect a warning.
(void) getcwd ( s, sizeof s ); // I expect no warning.
return 0; }
Compilation output:
$ gcc -o /tmp/getcwd test.c
[Compilation succeeds without any output.]
$ gcc -Wall -Wextra -o /tmp/getcwd test.c
[Compilation succeeds without any output.]
$ gcc -Wunused-result -o /tmp/getcwd test.c
[Compilation succeeds without any output.]
$ gcc -Os -o /tmp/getcwd test.c
test.c: In function ‘main’:
test.c:4:11: warning: ignoring return value of ‘getcwd’ declared with attribute
‘warn_unused_result’ [-Wunused-result]
4 | ; getcwd ( s, sizeof s ); // I expect a warning.
| ^~~~~~~~~~~~~~~~~~~~~~
test.c:5:11: warning: ignoring return value of ‘getcwd’ declared with attribute
‘warn_unused_result’ [-Wunused-result]
5 | (void) getcwd ( s, sizeof s ); // I expect no warning.
| ^~~~~~~~~~~~~~~~~~~~~~
Possibly related:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39808
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94389
Tested on Ubuntu 23.04 with gcc 12.2.0. I believe Ubuntu 22.04 with gcc 11.3.0
behaves identically.
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/12/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
12.2.0-17ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-12
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-12-Pa930Z/gcc-12-12.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-12-Pa930Z/gcc-12-12.2.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.2.0 (Ubuntu 12.2.0-17ubuntu1)
