[PATCH][alpha] Fix ____longjmp_chk

[Andreas Schwab]

You can use the various C implementations of ____longjmp_chk as a model,
they are known working.  The point of the test is to look whether
longjmp jumps back to a stack frame that is already left, ie. the
function containing setjmp has already returned.  It does not (and
cannot) check whether longjmp jumps to some random frame that may be
part of a different thread's stack, for example.  The sigaltstack check
is needed to allow jumping out of a signal frame on the alternate signal
stack.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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