'info threads' shows this about threads:
(gdb) info threads
11 Thread 0xb35a8b90 (LWP 23534) 0xb7f3c410 in __kernel_vsyscall ()
10 Thread 0xb3da9b90 (LWP 23533) 0xb7f3c410 in __kernel_vsyscall ()
9 Thread 0xb45aab90 (LWP 23532) 0xb7f3c410 in __kernel_vsyscall ()
...
* 1 Thread 0xb7f3a940 (LWP 23522) 0xb7f3c410 in __kernel_vsyscall ()
- First number is gdb's thread number.
- Second number is pthread's thread ID.
- Third number is matching kernel LWP (Light-Weight Process) ID
- Fourth number is address of function currently-executing in the
thread.
- Thread marked with '*' is the current thread.