Debugging with GDB Manual (5900-1473; WDB 6.2; January 2011)

print GDB should print a message when this signal happens.
noprint GDB should not mention the occurrence of the signal at all. This implies the
nostop keyword as well.
pass GDB should allow your program to see this signal; your program can handle
the signal, or else it may terminate if the signal is fatal and not handled.
nopass GDB should not allow your program to see this signal.
When a signal stops your program, the signal is not visible to the program until you
continue. Your program sees the signal then, if pass is in effect for the signal in question
at that time. In other words, after GDB reports a signal, you can use the handle command
with pass or nopass to control whether your program sees that signal when you
continue.
You can also use the signal command to prevent your program from seeing a signal,
or cause it to see a signal it normally would not see, or to give it any signal at any time.
For example, if your program stopped due to some sort of memory reference error, you
might store correct values into the erroneous variables and continue, hoping to see more
execution; but your program would probably terminate immediately as a result of the
fatal signal once it saw the signal. To prevent this, you can continue with 'signal 0'.
See “Giving your program a signal” (page 115).
5.4 Stopping and starting multi-thread programs
When your program has multiple threads (see “Debugging programs with multiple
threads” (page 41)), you can choose whether to set breakpoints on all threads, or on a
particular thread.
break linespec thread
threadno, break linespec
thread threadno if ...
linespec specifies source lines; there are several
ways of writing them, but the effect is always to
specify some source line.
Use the qualifier 'thread threadno' with a
breakpoint command to specify that you only want
GDB to stop the program when a particular thread
reaches this breakpoint. threadno is one of the
numeric thread identifiers assigned by GDB,
shown in the first column of the 'info threads'
display.
If you do not specify 'thread threadno' when
you set a breakpoint, the breakpoint applies to
all threads of your program.
You can use the thread qualifier on conditional
breakpoints as well; in this case, place 'thread
threadno' before the breakpoint condition, like
this:
64 Stopping and Continuing