https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101451
Bug ID: 101451
Summary: Incorrect -Wstringop-truncation warning
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: quentin at armitage dot org.uk
Target Milestone: ---
Created attachment 51151
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51151&action=edit
The .i file produced by the compile command
Command: gcc -v -save-temps -Wstringop-truncation -O2 -o strncat1 strncat1.c
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-11.1.1-20210531/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 11.1.1 20210531 (Red Hat 11.1.1-3) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wstringop-truncation' '-O2' '-o'
'strncat1' '-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-redhat-linux/11/cc1 -E -quiet -v strncat1.c
-mtune=generic -march=x86-64 -Wstringop-truncation -O2 -fpch-preprocess -o
strncat1.i
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/11/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/11/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-redhat-linux/11/include
/usr/local/include
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wstringop-truncation' '-O2' '-o'
'strncat1' '-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-redhat-linux/11/cc1 -fpreprocessed strncat1.i -quiet
-dumpbase strncat1.c -dumpbase-ext .c -mtune=generic -march=x86-64 -O2
-Wstringop-truncation -version -o strncat1.s
GNU C17 (GCC) version 11.1.1 20210531 (Red Hat 11.1.1-3) (x86_64-redhat-linux)
compiled by GNU C version 11.1.1 20210531 (Red Hat 11.1.1-3), GMP
version 6.2.0, MPFR version 4.1.0-p13, MPC version 1.2.1, isl version
isl-0.18-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C17 (GCC) version 11.1.1 20210531 (Red Hat 11.1.1-3) (x86_64-redhat-linux)
compiled by GNU C version 11.1.1 20210531 (Red Hat 11.1.1-3), GMP
version 6.2.0, MPFR version 4.1.0-p13, MPC version 1.2.1, isl version
isl-0.18-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 147699dd2c10be2630d381074a06fb9f
strncat1.c: In function ‘bad’:
strncat1.c:12:30: warning: ‘strncat’ output may be truncated copying 15 bytes
from a string of length 15 [-Wstringop-truncation]
12 | do { dest[0] = '\0'; strncat(dest, src, sizeof(dest) - 1); }
while (0);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wstringop-truncation' '-O2' '-o'
'strncat1' '-mtune=generic' '-march=x86-64'
as -v --64 -o strncat1.o strncat1.s
GNU assembler version 2.35.1 (x86_64-redhat-linux) using BFD version version
2.35.1-41.fc34
COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/11/:/usr/libexec/gcc/x86_64-redhat-linux/11/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/11/:/usr/lib/gcc/x86_64-redhat-linux/
LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/11/:/usr/lib/gcc/x86_64-redhat-linux/11/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/11/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wstringop-truncation' '-O2' '-o'
'strncat1' '-mtune=generic' '-march=x86-64' '-dumpdir' 'strncat1.'
/usr/libexec/gcc/x86_64-redhat-linux/11/collect2 -plugin
/usr/libexec/gcc/x86_64-redhat-linux/11/liblto_plugin.so
-plugin-opt=/usr/libexec/gcc/x86_64-redhat-linux/11/lto-wrapper
-plugin-opt=-fresolution=strncat1.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --build-id
--no-add-needed --eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -o strncat1
/usr/lib/gcc/x86_64-redhat-linux/11/../../../../lib64/crt1.o
/usr/lib/gcc/x86_64-redhat-linux/11/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/11/crtbegin.o
-L/usr/lib/gcc/x86_64-redhat-linux/11
-L/usr/lib/gcc/x86_64-redhat-linux/11/../../../../lib64 -L/lib/../lib64
-L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/11/../../.. strncat1.o
-lgcc --push-state --as-needed -lgcc_s --pop-state -lc -lgcc --push-state
--as-needed -lgcc_s --pop-state /usr/lib/gcc/x86_64-redhat-linux/11/crtend.o
/usr/lib/gcc/x86_64-redhat-linux/11/../../../../lib64/crtn.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wstringop-truncation' '-O2' '-o'
'strncat1' '-mtune=generic' '-march=x86-64' '-dumpdir' 'strncat1.'
System type
===========
Fedora 34
Command line triggering bug
===========================
gcc -Wstringop-truncation -O2 -o strncat1 strncat1.c
Expected behaviour
==================
No -Wstringop-truncation warning
Actual behaviour
================
A -Wstringop-truncation warning is issued
Other information
=================
The warning is not issued unless both -Wstringop-truncation and -O2 are
specified.
In my code I also get a -Wstringop-truncation warning when using strcpy_safe
defined as follows:
#define strcpy_safe(dst, src) \
do { strncpy(dst, src, sizeof(dst) - 1); dst[sizeof(dst) - 1] = '\0'; }
while (0)
However, I cannot produce a simple test case to reproduce it.
