At least with macOS Sequoia 15.5 and Xcode 16.3: $ cat test.cc #include <locale.h> #include <string.h> #include <xlocale.h> int main(void) { locale_t l = newlocale(LC_ALL_MASK, "el_GR.UTF-8", 0); strxfrm_l(NULL, "ό", 0, l); return 0; } $ c99 test.c && ./a.out Assertion failed: (p->val == key), function lookup_substsearch, file collate.c, line 596. Abort trap: 6

At least on $ uname -r -v -m 25.2.0 Darwin Kernel Version 25.2.0: Tue Nov 18 21:09:55 PST 2025; root:xnu-12377.61.12~1/RELEASE_ARM64_T8103 arm64 running the Posix program test.c #include <errno.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <sys/wait.h> #include <unistd.h> int main() { pid_t ch = fork(); if (ch == -1) { perror("fork"); return EXIT_FAILURE; } if (ch == 0) { return EXIT_SUCCESS; } if (setpgid(ch, ch) == -1) { perror("setpgid"); return EXIT_FAILURE; } siginfo_t stat; if (waitid(P_PID, ch, &stat, WEXITED | WNOWAIT) == -1) { perror("waitid"); return EXIT_FAILURE; } if (kill(-ch, SIGKILL) == -1) { perror("kill"); return EXIT_FAILURE; } return EXIT_SUCCESS; } as $ clang test.c $ ./a.out kill: Operation not permitted fails with EPERM even though the lifetime of the process group has not yet ended (due to the WNOWAIT).