Re: what marks the end of stack?

["Oliver Kowalke" <oliver.kowalke@xxxxxx>]

> "Oliver Kowalke" <oliver.kowalke@xxxxxx> writes:
> 
> > What marks the end of stack or how does uw_frame_state_for() detect the
> end of stack?
> > I've a coroutine library and I'm using _Unwind_ForcedUnwind() for stack
> cleanup. Function _Unwind_ForcedUnwind_Phase2() never sets
> _URC_END_OF_STACK!
> 
> What happens when it goes past the top of the stack?

I get an segmentation fault from _Uwind_resume().

> Normally the unwinder returns _URC_END_OF_STACK when it finds a stack
> frame with a PC value with no associated FDE.  A specific such PC value
> is zero.

In the example _URC_END_OF_STACK is not returned. A simple memory chunk is used as stack. Maybe I've to append a special page at the end of the stack - or something else?

I hopefuly the issue can be fixed.

best regards,
Oliver

test code with segfault:

#include <ucontext.h>
#include <unwind.h>

#include <cstdlib>
#include <cstring>
#include <iostream>
#include <vector>

static int counter = 0;
static ucontext_t ucf, ucm;

struct X
{
	X()
	{ std::cout << "X()" << std::endl; }

	~X()
	{ std::cout << "~X()" << std::endl; }
};

_Unwind_Reason_Code stop(
		int version,
		_Unwind_Action actions,
		_Unwind_Exception_Class exc_class,
		_Unwind_Exception *exc,
		_Unwind_Context *context,
		void * param) {

//	std::cout << "counter == " << ++counter << std::endl;

	if ( actions & _UA_END_OF_STACK) {
		std::cout << "end of stack, jump back" << std::endl;
		_Unwind_DeleteException( exc);
		if ( ::swapcontext( & ucf, & ucm) == -1)
			::abort();
	}

	return _URC_NO_REASON;
}

void force_unwind()
{
	_Unwind_Exception * exc = new _Unwind_Exception;
	std::memset( exc, 0, sizeof( * exc) );
	_Unwind_ForcedUnwind( exc, stop, 0);
}

void f( int i) {
	if ( i > 0) {
		X x;
		f( --i);
	} else {
		force_unwind();
		std::cout << "fini" << std::endl;
	}
}

int main( int argc, char * argv[]) {
	std::vector< char > fn_stack(16384, '\0');

	if ( ::getcontext( & ucf) == -1)
		::abort();
	ucf.uc_stack.ss_sp = & fn_stack[0];
	ucf.uc_stack.ss_size = fn_stack.size();
	::makecontext( & ucf, (void(*)())( f), 1, 5);

	if ( ::swapcontext( & ucm, & ucf) == -1)
		::abort();

	std::cout << "done" << std::endl;
	return 0;
}
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