[PATCH][gdb/threads] Fix lin_thread_get_thread_signals for glibc 2.28

Tom de Vries
2021-02-05T11:15:10Z

Hi,

When running test-case gdb.threads/create-fail.exp on openSUSE Factory
(with glibc version 2.32) I run into:
...
(gdb) continue
Continuing.
[New Thread 0x7ffff7c83700 (LWP 626354)]
[New Thread 0x7ffff7482700 (LWP 626355)]
[Thread 0x7ffff7c83700 (LWP 626354) exited]
[New Thread 0x7ffff6c81700 (LWP 626356)]
[Thread 0x7ffff7482700 (LWP 626355) exited]
[New Thread 0x7ffff6480700 (LWP 626357)]
[Thread 0x7ffff6c81700 (LWP 626356) exited]
[New Thread 0x7ffff5c7f700 (LWP 626358)]
[Thread 0x7ffff6480700 (LWP 626357) exited]
pthread_create: 22: Invalid argument

Thread 6 "create-fail" received signal SIG32, Real-time event 32.
[Switching to Thread 0x7ffff5c7f700 (LWP 626358)]
0x00007ffff7d87695 in clone () from /lib64/libc.so.6
(gdb) FAIL: gdb.threads/create-fail.exp: iteration 1: run till end
...
The problem is that glibc-internal signal SIGCANCEL is not recognized by gdb.

There's code in check_thread_signals that is supposed to take care of that,
but it's not working because this code in lin_thread_get_thread_signals has
stopped working:
...
/* NPTL reserves the first two RT signals, but does not provide any
way for the debugger to query the signal numbers - fortunately
they don't change. */
sigaddset (set, __SIGRTMIN);
sigaddset (set, __SIGRTMIN + 1);
...

Since glibc commit d2dc5467c6 "Filter out NPTL internal signals (BZ #22391)"
(first released as part of glibc 2.28), a sigaddset with a glibc-internal
signal has no other effect than setting errno to EINVALID.

Fix this by eliminating the usage of sigset_t in check_thread_signals and
lin_thread_get_thread_signals.

Tested on x86_64-linux.

Any comments?

Thanks,
- Tom

[gdb/threads] Fix lin_thread_get_thread_signals for glibc 2.28

gdb/ChangeLog:

2021-02-05 Tom de Vries <tdevries@suse.de>

PR threads/26228
* linux-nat.c (lin_thread_get_thread_signals): Remove.
(lin_thread_signals): New static var.
(lin_thread_get_thread_signal_num, lin_thread_get_thread_signal):
New function.
* linux-nat.h (lin_thread_get_thread_signals): Remove.
(lin_thread_get_thread_signal_num, lin_thread_get_thread_signal):
Declare.
* linux-thread-db.c (check_thread_signals): Use
lin_thread_get_thread_signal_num and lin_thread_get_thread_signal.

---
gdb/linux-nat.c | 26 +++++++++++++++++---------
gdb/linux-nat.h | 7 +++++--
gdb/linux-thread-db.c | 21 +++++----------------
3 files changed, 27 insertions(+), 27 deletions(-)

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 10419dc7bb5..42dcd77ac45 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -4411,16 +4411,24 @@ Enables printf debugging output."),
the GNU/Linux Threads library and therefore doesn't really belong
here. */

-/* Return the set of signals used by the threads library in *SET. */
+/* NPTL reserves the first two RT signals, but does not provide any
+ way for the debugger to query the signal numbers - fortunately
+ they don't change. */
+static int lin_thread_signals[] = { __SIGRTMIN, __SIGRTMIN + 1 };

-void
-lin_thread_get_thread_signals (sigset_t *set)
+/* See linux-nat.h. */
+
+unsigned int
+lin_thread_get_thread_signal_num (void)
{
- sigemptyset (set);
+ return sizeof (lin_thread_signals) / sizeof (lin_thread_signals[0]);
+}

- /* NPTL reserves the first two RT signals, but does not provide any
- way for the debugger to query the signal numbers - fortunately
- they don't change. */
- sigaddset (set, __SIGRTMIN);
- sigaddset (set, __SIGRTMIN + 1);
+/* See linux-nat.h. */
+
+int
+lin_thread_get_thread_signal (unsigned int i)
+{
+ gdb_assert (i < lin_thread_get_thread_signal_num ());
+ return lin_thread_signals[i];
}
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index a5547f282ad..ff4d753422d 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -304,8 +304,11 @@ void check_for_thread_db (void);
true on success, false if the process isn't using libpthread. */
extern int thread_db_notice_clone (ptid_t parent, ptid_t child);

-/* Return the set of signals used by the threads library. */
-extern void lin_thread_get_thread_signals (sigset_t *mask);
+/* Return the number of signals used by the threads library. */
+extern unsigned int lin_thread_get_thread_signal_num (void);
+
+/* Return the i-th signal used by the threads library. */
+extern int lin_thread_get_thread_signal (unsigned int i);

/* Find process PID's pending signal set from /proc/pid/status. */
void linux_proc_pending_signals (int pid, sigset_t *pending,
diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index dce4bd23c1b..4dab64ac344 100644
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -161,8 +161,6 @@ static thread_db_target the_thread_db_target;
/* Non-zero if we have determined the signals used by the threads
library. */
static int thread_signals;
-static sigset_t thread_stop_set;
-static sigset_t thread_print_set;

struct thread_db_info
{
@@ -1225,23 +1223,14 @@ check_thread_signals (void)
{
if (!thread_signals)
{
- sigset_t mask;
int i;

- lin_thread_get_thread_signals (&mask);
- sigemptyset (&thread_stop_set);
- sigemptyset (&thread_print_set);
-
- for (i = 1; i < NSIG; i++)
+ for (i = 0; i < lin_thread_get_thread_signal_num (); i++)
{
- if (sigismember (&mask, i))
- {
- if (signal_stop_update (gdb_signal_from_host (i), 0))
- sigaddset (&thread_stop_set, i);
- if (signal_print_update (gdb_signal_from_host (i), 0))
- sigaddset (&thread_print_set, i);
- thread_signals = 1;
- }
+ int sig = lin_thread_get_thread_signal (i);
+ signal_stop_update (gdb_signal_from_host (sig), 0);
+ signal_print_update (gdb_signal_from_host (sig), 0);
+ thread_signals = 1;
}
}
}