https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102337
Bug ID: 102337 Summary: possibly wrong warning about truncation Product: gcc Version: 11.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: rootkit85 at yahoo dot it Target Milestone: --- The following code: #include <stdio.h> // build with: -O2 -Werror=format-truncation void poke_kprobe_events(int add) { char cmd[192], probename[128], probefunc[128]; snprintf(probename, sizeof(probename), "a"); snprintf(probefunc, sizeof(probefunc), "b"); snprintf(cmd, sizeof(cmd), "%s %s", probename, probefunc); } Generates the following warning: $ gcc -O2 -c test.c -Werror=format-truncation test.c: In function ‘poke_kprobe_events’: test.c:11:40: error: ‘%s’ directive output may be truncated writing up to 127 bytes into a region of size between 64 and 191 [-Werror=format-truncation=] 11 | snprintf(cmd, sizeof(cmd), "%s %s", probename, probefunc); | ^~ ~~~~~~~~~ test.c:11:9: note: ‘snprintf’ output between 2 and 256 bytes into a destination of size 192 11 | snprintf(cmd, sizeof(cmd), "%s %s", probename, probefunc); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ cc1: some warnings being treated as errors I'm using the Fedora 34 packages: $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/11/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none 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,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 --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-11.2.1-20210728/obj-x86_64-redhat-linux/isl-install --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 11.2.1 20210728 (Red Hat 11.2.1-1) (GCC)