gdb/1847: Step over (next) fails in pthreads programs on recent (NPTL) RedHat Linuxes

[matb at enea dot se]

>Number:         1847
>Category:       gdb
>Synopsis:       Step over (next) fails in pthreads programs on recent (NPTL) RedHat Linuxes
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Tue Jan 18 10:28:00 UTC 2005
>Closed-Date:
>Last-Modified:
>Originator:     matb@enea.se
>Release:        GNU gdb Red Hat Linux (6.1post-1.20040607.17rh)
>Organization:
>Environment:
Linux viper 2.4.21-20.0.1.ELsmp #1 SMP Wed Nov 24 20:34:01 EST 2004 i686 athlon i386 GNU/Linux
gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-42)
This GDB was configured as "i386-redhat-linux-gnu"...Using host libthread_db library "/lib/tls/libthread_db.so.1".
>Description:
Can't find a combination of GDB (5.2.1, 6.0, 6.1, 6.3) and recent RedHat Linuxes (Enterprise Linux 3, Fedora Core 2) in which step over (next) works with pthreads programs.

The symptoms vary slightly but the two most common cases is that we stop in __nptl_create_event() (on some configurations with the text "Thread Event Breakpoint: gdb should not stop!"), or that we loose control and the step never finishes.

The original program I was trying this with is a big beast that in addition to the pthreads primitives uses setjmp / longjmp, which seems to add to the problems. 

However even simple programs, like the one attached, shows some of the problems. 
>How-To-Repeat:
--- Just set a breakpoint in the code run by one of the threads and try to step ---

(gdb) break main.c:46
Breakpoint 1 at 0x80488c0: file temp/main.c, line 46.
(gdb) run
Starting program: /homedirectories/home4/matb/ping 
[Thread debugging using libthread_db enabled]
[New Thread -1218598048 (LWP 24064)]
[New Thread -1219945552 (LWP 24067)]
[Switching to Thread -1219945552 (LWP 24067)]

Breakpoint 1, ping (p=0x0) at temp/main.c:46
46            swapin();
(gdb) delete 1
(gdb) n
[New Thread -1230435408 (LWP 24068)]

Program received signal SIGTRAP, Trace/breakpoint trap.
[Switching to Thread -1218598048 (LWP 24064)]
0xb75ce6f1 in __nptl_create_event () from /lib/tls/libpthread.so.0
(gdb) bt
#0  0xb75ce6f1 in __nptl_create_event () from /lib/tls/libpthread.so.0
#1  0xb6a90bb0 in ?? ()
#2  0xb75d59e0 in banner () from /lib/tls/libpthread.so.0
#3  0x027d0f00 in ?? ()
#4  0xb75ced50 in __free_tcb () from /lib/tls/libpthread.so.0
Previous frame inner to this frame (corrupt stack?)

--- or ---

(gdb) n
54               if (pthread_create(&t, NULL, pang, NULL))
(gdb) n
[New Thread -1262003280 (LWP 18224)]
59               threads[2] = t;
(gdb) n
61            i = (i+1) % 5;
(gdb) n
63            swapout();
(gdb) n
PONG! 44           for (;;)
(gdb) n
46            swapin();
(gdb) n
PANG! 47              printf("PING! ");
(gdb) n
48            fflush(stdout);
(gdb) n
PING! 49              sleep(1);
(gdb) n
[Thread -1262003280 (zombie) exited]
PONG! PING! PONG! PING! PONG! PING! PONG! PING! PONG! 
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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