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Fix fork after recovered stack overflow

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* fork.cc (frok::parent): Set stacktop value based on requested stack
	pointer value in child.  Explain why.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen
2015-07-01 15:28:16 +02:00
parent 0f3e631571
commit e3d345c5c3
2 changed files with 19 additions and 2 deletions
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16
winsup/cygwin/fork.cc
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@ -308,9 +308,21 @@ frok::parent (volatile char * volatile stack_here)
ch.forker_finished = forker_finished;
PTEB teb = NtCurrentTeb ();
ch.stackbottom = _tlsbase;
ch.stacktop = (void *) _tlstop;
ch.stackaddr = teb->DeallocationStack;
ch.stackbottom = _tlsbase;
/* If DeallocationStack is NULL, we're running on an application-provided
stack. If so, the entire stack is committed anyway and StackLimit points
to the allocation address of the stack. Otherwise we're running on a
system-allocated stack and using StackLimit is dangerous, in case the
application encountered a stack overflow and recovered from it via
a signal handler running on an alternate stack. Since stack_here is
the address of the stack pointer we start the child with anyway, we
can set ch.stacktop to this value rounded down to page size. The
child will not need the rest of the stack anyway. */
if (!ch.stackaddr)
ch.stacktop = _tlstop;
else
ch.stacktop = (void *) ((uintptr_t) stack_here & ~wincap.page_size ());
ch.guardsize = 0;
if (&_my_tls != _main_tls)
{