You can use catchpoints to cause the debugger to stop for certain
kinds of program events, such as C++ exceptions or the loading of a
shared library. Use the catch command to set a catchpoint.
catch event
Stop when event occurs. event can be any of the following:
throw
The throwing of a C++ exception.
catch
The catching of a C++ exception.
exec
A call to exec. This is currently only available for HP-UX.
fork
A call to fork. This is currently only available for HP-UX.
vfork
A call to vfork. This is currently only available for HP-UX.
load
load libname
The dynamic loading of any shared library, or the loading of the library
libname. This is currently only available for HP-UX.
unload
unload libname
The unloading of any dynamically loaded shared library, or the unloading
of the library libname. This is currently only available for HP-UX.
tcatch event
Set a catchpoint that is enabled only for one stop. The catchpoint is
automatically deleted after the first time the event is caught.
Use the info break command to list the current catchpoints.
There are currently some limitations to C++ exception handling
(catch throw and catch catch) in GDB:
If you call a function interactively, GDB normally returns
control to you when the function has finished executing. If the call
raises an exception, however, the call may bypass the mechanism that
returns control to you and cause your program either to abort or to
simply continue running until it hits a breakpoint, catches a signal
that GDB is listening for, or exits. This is the case even if
you set a catchpoint for the exception; catchpoints on exceptions are
disabled within interactive calls.
You cannot raise an exception interactively.
You cannot install an exception handler interactively.
Sometimes catch is not the best way to debug exception handling:
if you need to know exactly where an exception is raised, it is better to
stop before the exception handler is called, since that way you
can see the stack before any unwinding takes place. If you set a
breakpoint in an exception handler instead, it may not be easy to find
out where the exception was raised.
To stop just before an exception handler is called, you need some
knowledge of the implementation. In the case of GNU C++, exceptions are
raised by calling a library function named __raise_exception
which has the following ANSI C interface:
/* addr is where the exception identifier is stored.
id is the exception identifier. */
void __raise_exception (void **addr, void *id);
To make the debugger catch all exceptions before any stack
unwinding takes place, set a breakpoint on __raise_exception
(see section Breakpoints; watchpoints; and exceptions).
With a conditional breakpoint (see section Break conditions)
that depends on the value of id, you can stop your program when
a specific exception is raised. You can use multiple conditional
breakpoints to stop your program when any of a number of exceptions are
raised.