Date: Thu, 17 Apr 2025 02:23:21 GMT From: Kyle Evans <kevans@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 04f7496f89e2 - stable/13 - libc: allow __cxa_atexit handlers to be added during __cxa_finalize Message-ID: <202504170223.53H2NLTe011180@gitrepo.freebsd.org>
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The branch stable/13 has been updated by kevans: URL: https://cgit.FreeBSD.org/src/commit/?id=04f7496f89e28057079f3f0b1a02d7d9d874487f commit 04f7496f89e28057079f3f0b1a02d7d9d874487f Author: Aurélien Croc de Suray <freebsd@ap2c.com> AuthorDate: 2025-04-05 00:47:53 +0000 Commit: Kyle Evans <kevans@FreeBSD.org> CommitDate: 2025-04-17 01:02:12 +0000 libc: allow __cxa_atexit handlers to be added during __cxa_finalize science/dlib-cpp reveals an interesting scenario that works fine on other platforms but not on FreeBSD; notably, it ends up creating a new global object from some destructor which is called during __cxa_finalize. This breaks when libdlib is dlopen()ed and then subsequently dlclose()ed, as we never end up invoking the created object's dtor until program exit when the shlib is already unmapped. Fix it by noting when we're in the middle of __cxa_finalize for a dso, and then restarting the search if __cxa_atexit() was called in the middle somewhere. We wait until we've processed the initial set before starting over and processing the newly added handlers as if it were a complete set of handlers added during runtime. The alternative is calling them as they're added to maintain a LIFO in terms of total ordering, but in theory a constructor could add another global object that also needs to be destroyed, and that object needs to be destroyed after the one that constructed it to avoid creating unexpected lifetime issues. This manifests in the pdlib PHP extension for dlib crashing, see [0]. [0] https://github.com/goodspb/pdlib/issues/39 PR: 285870 Reviewed by: kevans (also supplied commit message) (cherry picked from commit 23427c8e1fedb9fc68ad0bd27a59c7ffd2b3008c) --- lib/libc/stdlib/atexit.c | 61 ++++++++++++++++++++++++++++-------------------- 1 file changed, 36 insertions(+), 25 deletions(-) diff --git a/lib/libc/stdlib/atexit.c b/lib/libc/stdlib/atexit.c index 6b63d9e728c4..5b39552821ed 100644 --- a/lib/libc/stdlib/atexit.c +++ b/lib/libc/stdlib/atexit.c @@ -39,6 +39,7 @@ static char sccsid[] = "@(#)atexit.c 8.2 (Berkeley) 7/3/94"; #include "namespace.h" #include <errno.h> #include <link.h> +#include <stdbool.h> #include <stddef.h> #include <stdlib.h> #include <unistd.h> @@ -60,6 +61,8 @@ _Block_copy(void*); #define ATEXIT_FN_CXA 2 static pthread_mutex_t atexit_mutex = PTHREAD_MUTEX_INITIALIZER; +static void *current_finalize_dso = NULL; +static bool call_finalize_again = false; #define _MUTEX_LOCK(x) if (__isthreaded) _pthread_mutex_lock(x) #define _MUTEX_UNLOCK(x) if (__isthreaded) _pthread_mutex_unlock(x) @@ -119,6 +122,9 @@ atexit_register(struct atexit_fn *fptr) __atexit = p; } p->fns[p->ind++] = *fptr; + if (current_finalize_dso != NULL && + current_finalize_dso == fptr->fn_dso) + call_finalize_again = true; _MUTEX_UNLOCK(&atexit_mutex); return 0; } @@ -212,33 +218,38 @@ __cxa_finalize(void *dso) } _MUTEX_LOCK(&atexit_mutex); - for (p = __atexit; p; p = p->next) { - for (n = p->ind; --n >= 0;) { - if (p->fns[n].fn_type == ATEXIT_FN_EMPTY) - continue; /* already been called */ - fn = p->fns[n]; - if (dso != NULL && dso != fn.fn_dso) { - /* wrong DSO ? */ - if (!has_phdr || global_exit || - !__elf_phdr_match_addr(&phdr_info, - fn.fn_ptr.cxa_func)) - continue; + current_finalize_dso = dso; + do { + call_finalize_again = false; + for (p = __atexit; p; p = p->next) { + for (n = p->ind; --n >= 0;) { + if (p->fns[n].fn_type == ATEXIT_FN_EMPTY) + continue; /* already been called */ + fn = p->fns[n]; + if (dso != NULL && dso != fn.fn_dso) { + /* wrong DSO ? */ + if (!has_phdr || global_exit || + !__elf_phdr_match_addr(&phdr_info, + fn.fn_ptr.cxa_func)) + continue; + } + /* + Mark entry to indicate that this particular + handler has already been called. + */ + p->fns[n].fn_type = ATEXIT_FN_EMPTY; + _MUTEX_UNLOCK(&atexit_mutex); + + /* Call the function of correct type. */ + if (fn.fn_type == ATEXIT_FN_CXA) + fn.fn_ptr.cxa_func(fn.fn_arg); + else if (fn.fn_type == ATEXIT_FN_STD) + fn.fn_ptr.std_func(); + _MUTEX_LOCK(&atexit_mutex); } - /* - Mark entry to indicate that this particular handler - has already been called. - */ - p->fns[n].fn_type = ATEXIT_FN_EMPTY; - _MUTEX_UNLOCK(&atexit_mutex); - - /* Call the function of correct type. */ - if (fn.fn_type == ATEXIT_FN_CXA) - fn.fn_ptr.cxa_func(fn.fn_arg); - else if (fn.fn_type == ATEXIT_FN_STD) - fn.fn_ptr.std_func(); - _MUTEX_LOCK(&atexit_mutex); } - } + } while (call_finalize_again); + current_finalize_dso = NULL; _MUTEX_UNLOCK(&atexit_mutex); if (dso == NULL) _MUTEX_DESTROY(&atexit_mutex);
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