The diff below implements __cxa_thread_atexit(). Calls to this
function are emitted by the compiler to schedule running desctructors
for thread_local objects when a thread terminates or calls exit(3).
The Linux implementation prevents unloading of shared libraries that
registered such destructors to prevent things from crashing. This
diff does not implement that functionality yet. I plan to add that
later. I expect this to be a bit of a corner case.
I've chosen to implement __cxa_thread_atexit() directly instead of
__cxa_thread_atexit_impl(). I think that is cleaner. It means we
don't need to make changes to libc++ for this to start working. It
looks like modern libstdc++ version will detect __cxa_thread_atexit().
This adds a member to the "TIB". Tis means that you'll need to
install the new headers and rebuild ld.so before rebuilding libpthread
and libc.
This will require a libc minor bump. But maybe it could ride the
scheduled major bump?
Index: include/tib.h
===================================================================
RCS file: /cvs/src/include/tib.h,v
retrieving revision 1.4
diff -u -p -r1.4 tib.h
--- include/tib.h 20 Apr 2017 16:07:52 -0000 1.4
+++ include/tib.h 11 Aug 2017 14:20:30 -0000
@@ -135,6 +135,7 @@
*/
struct tib {
+ void *tib_atexit;
int tib_thread_flags; /* internal to libpthread */
pid_t tib_tid;
int tib_cantcancel;
@@ -182,6 +183,7 @@ struct tib {
int tib_cantcancel;
pid_t tib_tid;
int tib_thread_flags; /* internal to libpthread */
+ void *tib_atexit;
#if !defined(__LP64__) && !defined(__i386)
int __tib_padding; /* padding for 8byte alignment */
#endif
@@ -207,6 +209,7 @@ struct tib {
#define TIB_INIT(tib, dtv, thread) do { \
(tib)->tib_thread = (thread); \
+ (tib)->tib_atexit = NULL; \
(tib)->tib_locale = NULL; \
(tib)->tib_cantcancel = 0; \
(tib)->tib_cancel_point = 0; \
Index: lib/librthread/rthread.c
===================================================================
RCS file: /cvs/src/lib/librthread/rthread.c,v
retrieving revision 1.95
diff -u -p -r1.95 rthread.c
--- lib/librthread/rthread.c 27 Jul 2017 16:35:08 -0000 1.95
+++ lib/librthread/rthread.c 11 Aug 2017 14:20:30 -0000
@@ -331,6 +331,12 @@ pthread_exit(void *retval)
oclfn->fn(oclfn->arg);
free(oclfn);
}
+ while (tib->tib_atexit) {
+ struct thread_atexit_fn *fnp = tib->tib_atexit;
+ tib->tib_atexit = fnp->next;
+ fnp->func(fnp->arg);
+ free(fnp);
+ }
_rthread_tls_destructors(thread);
_spinlock(&_thread_lock);
LIST_REMOVE(thread, threads);
Index: lib/libc/Symbols.list
===================================================================
RCS file: /cvs/src/lib/libc/Symbols.list,v
retrieving revision 1.54
diff -u -p -r1.54 Symbols.list
--- lib/libc/Symbols.list 19 Jun 2017 03:06:26 -0000 1.54
+++ lib/libc/Symbols.list 11 Aug 2017 14:20:30 -0000
@@ -1420,6 +1420,7 @@ random
/* stdlib */
_Exit
__cxa_atexit
+__cxa_thread_atexit
__cxa_finalize
__isthreaded
a64l
Index: lib/libc/include/thread_private.h
===================================================================
RCS file: /cvs/src/lib/libc/include/thread_private.h,v
retrieving revision 1.29
diff -u -p -r1.29 thread_private.h
--- lib/libc/include/thread_private.h 15 Oct 2016 18:24:40 -0000 1.29
+++ lib/libc/include/thread_private.h 11 Aug 2017 14:20:31 -0000
@@ -96,6 +96,12 @@ struct thread_callbacks {
__pid_t (*tc_vfork)(void);
};
+struct thread_atexit_fn {
+ void (*func)(void *);
+ void *arg;
+ struct thread_atexit_fn *next;
+};
+
__BEGIN_PUBLIC_DECLS
/*
* Set the callbacks used by libc
Index: lib/libc/stdlib/atexit.c
===================================================================
RCS file: /cvs/src/lib/libc/stdlib/atexit.c,v
retrieving revision 1.24
diff -u -p -r1.24 atexit.c
--- lib/libc/stdlib/atexit.c 10 Nov 2015 04:14:03 -0000 1.24
+++ lib/libc/stdlib/atexit.c 11 Aug 2017 14:20:31 -0000
@@ -38,6 +38,8 @@
#include "atfork.h"
#include "thread_private.h"
+#include "tib.h"
+
struct atexit *__atexit;
static int restartloop;
@@ -121,6 +123,25 @@ atexit(void (*fn)(void))
}
DEF_STRONG(atexit);
+int
+__cxa_thread_atexit(void (*func)(void *), void *arg, void *dso)
+{
+ struct thread_atexit_fn *fnp;
+ struct tib *tib = TIB_GET();
+
+ fnp = calloc(1, sizeof(struct thread_atexit_fn));
+ if (fnp == NULL)
+ return -1;
+
+ fnp->func = func;
+ fnp->arg = arg;
+ fnp->next = tib->tib_atexit;
+ tib->tib_atexit = fnp;
+
+ return 0;
+}
+DEF_STRONG(__cxa_thread_atexit);
+
/*
* Call all handlers registered with __cxa_atexit() for the shared
* object owning 'dso'.
@@ -129,10 +150,20 @@ DEF_STRONG(atexit);
void
__cxa_finalize(void *dso)
{
+ struct tib *tib = TIB_GET();
struct atexit *p, *q;
struct atexit_fn fn;
int n, pgsize = getpagesize();
static int call_depth;
+
+ if (dso == NULL) {
+ while (tib->tib_atexit) {
+ struct thread_atexit_fn *fnp = tib->tib_atexit;
+ tib->tib_atexit = fnp->next;
+ fnp->func(fnp->arg);
+ free(fnp);
+ }
+ }
_ATEXIT_LOCK();
call_depth++;
Index: lib/libc/stdlib/atexit.h
===================================================================
RCS file: /cvs/src/lib/libc/stdlib/atexit.h,v
retrieving revision 1.10
diff -u -p -r1.10 atexit.h
--- lib/libc/stdlib/atexit.h 25 Oct 2015 18:01:24 -0000 1.10
+++ lib/libc/stdlib/atexit.h 11 Aug 2017 14:20:31 -0000
@@ -46,7 +46,9 @@ extern struct atexit *__atexit; /* poin
__END_HIDDEN_DECLS
int __cxa_atexit(void (*)(void *), void *, void *);
+int __cxa_thread_atexit(void (*)(void *), void *, void *);
void __cxa_finalize(void *);
PROTO_NORMAL(__cxa_atexit);
+PROTO_NORMAL(__cxa_thread_atexit);
PROTO_NORMAL(__cxa_finalize);
