From: George Foot <mert0407 AT sable DOT ox DOT ac DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Signal handlers -- what can they do?
Date: 14 Jun 1998 06:05:04 GMT
Organization: Oxford University, England
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To: djgpp AT delorie DOT com
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I'm not completely sure what context signal handlers are called in.
Any comments on the following questions would be appreciated.

1) Are any of the following functions remotely dangerous things to
call in a signal handler?  Some are used in the default handler, so I
presume they are reasonably safe.

    __dpmi_get_segment_base_address
    __dpmi_get_segment_limit
    __dpmi_get_memory_block_size_and_base
    setjmp
    exit, _exit
    _creat, _write, _close
    signal, raise

2) Should the memory touched be locked?  I'm not sure what the
difference is between a hardware exception and a software exception.
As far as I understand it, the SIG* signals are all software
exceptions; is that right?

3) What are the consequences, within the signal handler, of
terminating the program with `_exit' rather than `exit'?  The default
signal handler calls one in some circumstances, the other in other
circumstances; I'm not sure why it does this.

4) As far as I can tell, my SS:ESP in a signal handler is the same as
the main application's SS:ESP when the signal occured.  What happens
if the signal occured because of a stack problem?  Surely under these
circumstances we can't continue to use the same stack.

Thanks in advance for any of this information.

-- 
george DOT foot AT merton DOT oxford DOT ac DOT uk

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