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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 “Breakpoints” (page 51)).
With a conditional breakpoint (see “Break conditions” (page 59)) 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.
5.1 Breakpoints 57