nptl_db: Support different libpthread/ld.so load orders (bug 27744)

libthread_db is loaded once GDB encounters libpthread, and at this
point, ld.so may not have been processed by GDB yet. As a result,
_rtld_global cannot be accessed by regular means from libthread_db.
To make this work until GDB can be fixed, acess _rtld_global through
a pointer stored in libpthread.

The new test does not reproduce bug 27744 with
--disable-hardcoded-path-in-tests, but is still a valid smoke test.
With --enable-hardcoded-path-in-tests, it is necessary to avoid
add-symbol-file because this can tickle a GDB bug.

Fixes commit 1daccf403b1bd86370eb94edca794dc106d02039 ("nptl: Move
stack list variables into _rtld_global").

Tested-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit a64afc225240b2b27129ccfb0516d7c958b98040)

1 files changed, 8 insertions, 0 deletions

diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index 6c645aff48..f13d8e44a4 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -51,6 +51,14 @@ static td_thr_events_t __nptl_threads_events __attribute_used__;
 /* Pointer to descriptor with the last event.  */
 static struct pthread *__nptl_last_event __attribute_used__;
 
+#ifdef SHARED
+/* This variable is used to access _rtld_global from libthread_db.  If
+   GDB loads libpthread before ld.so, it is not possible to resolve
+   _rtld_global directly during libpthread initialization.  */
+static struct rtld_global *__nptl_rtld_global __attribute_used__
+  = &_rtld_global;
+#endif
+
 /* Number of threads running.  */
 unsigned int __nptl_nthreads = 1;