Re: am I misunderstanding exception frames
"andrew_nuss@yahoo.com" <andrew_nuss@yahoo.com> writes:
I am getting a hard-crash while using exception frames, or so it seems
by logging to a file. The crash occurs only in release mode with full
optimization.
My exception struct:
struct VMExitException {
EStruct* pstruct; // a pointer to a struct that needs
subrefing if not null
... // other members
// inline constructor
VMExitException (EStruct* s)
{
pstruct = s;
...
}
};
Then in the VM the following functions are not really inline:
class VM {
void Cleanup ();
void Execute ()
{
try {
Run();
} catch (VMExitException& e) {
Side note: It's a good idea to catch by reference to const.
if (e.pstruct)
e.pstruct->SubRef(); // crash because pstruct ptr
is garbage
Only if inside Run(), thisreg is first assigned to the address of an
object which is destructed before we arrive here. In the code you
posted, I think e.pstruct is guaranteed to be equal to 0.
Please post a simpler (in particular, leave out the VM class and the
opcode and codeblock parts), but complete program that your audience
can copy&paste&compile to see what you are seeing.
... // other cleanup
}
}
void Run()
{
EStruct* thisreg = 0;
do {
int opcode = codeblock[cursor++];
switch (opcode) {
... lots of cases
case EAtom::EXIT: {
// logging here shows that thisreg is null
// but we try to create a VMExitException and
when caught
// by caller the member pstruct is garbage
throw VMExitException(thisreg);
}
}
};
}
};
Do you guys see my concern. Is it legal to create an exception struct
on a frame of the inner function and then catch it by reference in the
outer?
Yes. The throw statement first copies its argument object to a special
place in memory.
If so, how is it possible that the frame of the inner is
preserved in the catch block of the outer, and if not, how do I
accomplish the transfer of information from the inner's state to the
outer via an exception.
Through the copy-constructor of the exception class.
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