g++ EH stack

[Jason Merrill]

The languge-specific part of the EH stack in g++ contains these elements:

void *value; // pointer to the thrown object, or the thrown value itself if
	     // a pointer
void *type;  // pointer to the type_info node for the thrown object
void (*cleanup)(void *, int) // pointer to the destructor for the object
bool caught; // has this exception been caught since its last throw?
long handlers; // how many catch handlers are active for this exception

Both 'caught' and 'handlers' are needed to handle rethrowing and catching
within a catch block.

Language interaction is handled by recording the language of both the
exception region and the thrown exception.  Each thrown exception also
includes a pointer to a language-specific matching function which is called
to compare the types of the exception and handler.

Jason