https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
--- Comment #6 from Arnd Bergmann <arnd at linaro dot org> --- I figured out the qnx4 warning in the end: https://godbolt.org/z/hvqjr3 struct qnx4_inode_entry { char di_status; union { struct { char di_fname[16]; char di_pad[32]; }; struct { char dl_fname[48]; }; }; }; int qnx4_readdir(struct qnx4_inode_entry *de) { if (!de->di_fname[0]) return 0; if (de->di_status) return __builtin_strnlen(de->di_fname, sizeof(de->di_fname)); else return __builtin_strnlen(de->dl_fname, sizeof(de->dl_fname)); return 0; } This produces <source>:22:16: warning: '__builtin_strnlen' specified bound 48 exceeds source size 16 [-Wstringop-overread] because the first access on the object seems to decide which layout is assumed. Changing (!de->di_fname[0]) to (!de->dl_fname[0]) shuts up the warning since that is a longer field. This is probably enough as a workaround, if you can confirm that the behavior of the compiler is also intentional for this input.
