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authorPedro Alves <palves@redhat.com>2014-12-16 16:12:24 +0000
committerPedro Alves <palves@redhat.com>2015-01-09 11:41:01 +0000
commita33e39599ce39ec6225d71f7da1719b544740745 (patch)
tree6ae0a75c900c6f95e33ff3285b3912cd512863da /gdb/gdbserver/thread-db.c
parent8784d56326e72e2e6863e8443b1f97e45a46ba36 (diff)
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libthread_db: Skip attaching to terminated and joined threads
I wrote a test that attaches to a program that constantly spawns short-lived threads, which exposed several issues. This is one of them. On GNU/Linux, attaching to a multi-threaded program sometimes prints out warnings like: ... [New LWP 20700] warning: unable to open /proc file '/proc/-1/status' [New LWP 20850] [New LWP 21019] ... That happens because when a thread exits, and is joined, glibc does: nptl/pthread_join.c: pthread_join () { ... if (__glibc_likely (result == 0)) { /* We mark the thread as terminated and as joined. */ pd->tid = -1; ... /* Free the TCB. */ __free_tcb (pd); } So if we attach or interrupt the program (which does an implicit "info threads") at just the right (or rather, wrong) time, we can find and return threads in the libthread_db/pthreads thread list with kernel thread ID -1. I've filed glibc PR nptl/17707 for this. You'll find more info there. This patch handles this as a special case in GDB. This is actually more than just a cosmetic issue. lin_lwp_attach_lwp will think that this -1 is an LWP we're not attached to yet, and after failing to attach will try to check we were already attached to the process, using a waitpid call, which in this case ends up being "waitpid (-1, ...", which obviously results in GDB potentially discarding an event when it shouldn't... Tested on x86_64 Fedora 20, native and gdbserver. gdb/gdbserver/ 2015-01-09 Pedro Alves <palves@redhat.com> * thread-db.c (find_new_threads_callback): Ignore thread if the kernel thread ID is -1. gdb/ 2015-01-09 Pedro Alves <palves@redhat.com> * linux-nat.c (lin_lwp_attach_lwp): Assert that the lwp id we're about to wait for is > 0. * linux-thread-db.c (find_new_threads_callback): Ignore thread if the kernel thread ID is -1.
Diffstat (limited to 'gdb/gdbserver/thread-db.c')
-rw-r--r--gdb/gdbserver/thread-db.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/gdb/gdbserver/thread-db.c b/gdb/gdbserver/thread-db.c
index 4e0d32a..b0d1f0d 100644
--- a/gdb/gdbserver/thread-db.c
+++ b/gdb/gdbserver/thread-db.c
@@ -396,6 +396,17 @@ find_new_threads_callback (const td_thrhandle_t *th_p, void *data)
if (err != TD_OK)
error ("Cannot get thread info: %s", thread_db_err_str (err));
+ if (ti.ti_lid == -1)
+ {
+ /* A thread with kernel thread ID -1 is either a thread that
+ exited and was joined, or a thread that is being created but
+ hasn't started yet, and that is reusing the tcb/stack of a
+ thread that previously exited and was joined. (glibc marks
+ terminated and joined threads with kernel thread ID -1. See
+ glibc PR17707. */
+ return 0;
+ }
+
/* Check for zombies. */
if (ti.ti_state == TD_THR_UNKNOWN || ti.ti_state == TD_THR_ZOMBIE)
return 0;