Junbo Zheng 7797b12244 libc/atexit: honor registrations made during exit processing ... atexit_call_exitfuncs() cached its loop bound on entry (for (idx = aehead->nfuncs - 1; idx >= 0; idx--)), while atexit_register() appends new entries at funcs[nfuncs] and bumps nfuncs. Any function registered by an exit handler via atexit() / on_exit() / __cxa_atexit() lands above the cached bound and is never invoked, even though the registration returns OK. This contradicts the exit(3) documentation that NuttX mirrors verbatim in its own exit() docstring (libs/libc/stdlib/lib_exit.c): It is possible for one of these functions to use atexit(3) or on_exit(3) to register an additional function to be executed during exit processing; the new registration is added to the front of the list of functions that remain to be called. The same restructure closes a second defect: atexit_call_exitfuncs() read and cleared the task-group-shared ta_exit list without holding ta_lock, while atexit_register() takes it ("The following must be atomic"). Entries are now claimed under the lock and the handler is invoked with the lock released, so a handler re-entering atexit_register() cannot deadlock (also safe with the non-recursive nxmutex used here). Evidence: exit(3) man page, DESCRIPTION - https://man7.org/linux/man-pages/man3/exit.3.html NuttX mirrors this passage verbatim in its own exit() docstring -- 5a209a853e/libs/libc/stdlib/lib_exit.c (L65-L70) Before: ``` A handler that registers another function during exit processing gets a success return from atexit(), but the new function is never invoked - it lands above the loop bound cached on entry. ``` After: ``` A registration made during exit processing runs before the older remaining handlers (order A -> B -> C below), matching the exit(3) guarantee, and the list is consumed under ta_lock. ``` Testing: Simulated (sim:nsh, CONFIG_LIBC_MAX_EXITFUNS=8). Build and run: ``` cmake -B build -DBOARD_CONFIG=sim:nsh -GNinja cmake -S . -B build # after setting CONFIG_LIBC_MAX_EXITFUNS=8 # in build/.config (sim:nsh default is 1) cmake --build build -j$(nproc) (echo hello; echo poweroff) | ./build/nuttx ``` "hello" runs the test at the NSH prompt; poweroff terminates the sim. The test was carried by apps/examples/hello/hello_main.c (scratch only, not part of this commit); its diff: ``` --- a/examples/hello/hello_main.c +++ b/examples/hello/hello_main.c @@ -24,6 +24,7 @@ #include <nuttx/config.h> #include <stdio.h> +#include <stdlib.h> /**************************************************************************** * Public Functions @@ -33,8 +34,29 @@ * hello_main ****************************************************************************/ +static void handler_b(void) +{ + printf("ATEXIT-TEST: handler B called (registered during exit)\n"); +} + +static void handler_a(void) +{ + int ret; + + printf("ATEXIT-TEST: handler A called\n"); + ret = atexit(handler_b); + printf("ATEXIT-TEST: atexit(handler_b) inside A returned %d\n", ret); +} + +static void handler_c(void) +{ + printf("ATEXIT-TEST: handler C called\n"); +} + int main(int argc, FAR char *argv[]) { printf("Hello, World!!\n"); + atexit(handler_c); /* older entry, must run LAST */ + atexit(handler_a); /* registers handler_b during exit */ return 0; } ``` Before the fix: ``` Hello, World!! ATEXIT-TEST: handler A called ATEXIT-TEST: atexit(handler_b) inside A returned 0 ATEXIT-TEST: handler C called ``` (handler B is never invoked although its registration returned 0) After the fix: ``` Hello, World!! ATEXIT-TEST: handler A called ATEXIT-TEST: atexit(handler_b) inside A returned 0 ATEXIT-TEST: handler B called (registered during exit) ATEXIT-TEST: handler C called ``` Assisted-by: Claude Code (GLM-5.3) <claude@anthropic.com> Signed-off-by: Junbo Zheng <zhengjunbo1@xiaomi.com>		2026-09-14 18:52:46 -03:00
..
libbuiltin	!sched/arch/libc: Give fork() and vfork() their real, separate semantics.	2026-08-10 08:57:30 -03:00
libc	libc/atexit: honor registrations made during exit processing	2026-09-14 18:52:46 -03:00
libdsp	tools: fix stale archive members surviving a Kconfig-driven CSRCS change	2026-07-28 21:26:03 -03:00
libm	cmake: Use NUTTX(_DIR/_BIN_DIR) instead CMAKE(_SRC_DIR/_BIN_DIR)	2026-08-09 11:13:08 -03:00
libnx	tools: fix stale archive members surviving a Kconfig-driven CSRCS change	2026-07-28 21:26:03 -03:00
libxx	cmake: Use NUTTX(_DIR/_BIN_DIR) instead CMAKE(_SRC_DIR/_BIN_DIR)	2026-08-09 11:13:08 -03:00
CMakeLists.txt	libs: migrate to SPDX identifier	2024-10-01 12:25:52 +08:00