I found this issue while compiling systemd-239 with gcc-9.3.0 The problem is in local data initialization on the stack such as array of pointers to global data. -O0 is fine, but -01,02,03 eliminates such data causing app to segfault. Confirmed gcc-9 branch (up to commit 25c60fcadc397c42a0ec778e5b1238888f2c94d3) still has this bug. Test program is attached below. Additional info and steps to reproduce: ~/gcc$ ./host-x86_64-pc-linux-gnu/gcc/xgcc -v Using built-in specs. COLLECT_GCC=./host-x86_64-pc-linux-gnu/gcc/xgcc Target: x86_64-pc-linux-gnu Configured with: ./configure --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-languages=c --disable-multilib --disable-bootstrap --disable-libstdcxx-pch --enable-linker-build-id --enable-plugin --with-system-zlib Thread model: posix gcc version 9.3.1 20200507 (GCC) ~/gcc$ ./host-x86_64-pc-linux-gnu/gcc/xgcc -B./host-x86_64-pc-linux-gnu/gcc/ test.c ~/gcc$ ./a.out ~/gcc$ echo $? 0 ~/gcc$ ./host-x86_64-pc-linux-gnu/gcc/xgcc -B./host-x86_64-pc-linux-gnu/gcc/ -O1 test.c ~/gcc$ ./a.out Segmentation fault (core dumped) ===================== test.c ========================== #include <string.h> int chararray(char **j) { if (!j) j = (char *[]){"a", "test"}; return (strlen(j[0]) == 1) & (strlen(j[1]) == 4); } int main(void) { return chararray(0) == 0; } =======================================================
> if (!j) j = (char *[]){"a", "test"}; The scope of the unnamed variable is just in that statement. So you are using the unnamed variable outside of the scope. See https://gcc.gnu.org/gcc-9/porting_to.html#complit See PR 91031 also which is this is a dup of. *** This bug has been marked as a duplicate of bug 91031 ***