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From:	"Charles Sandmann" <cwsdpmi AT earthlink DOT net>
Newsgroups:	comp.os.msdos.djgpp
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Subject:	Re: CC1.EXE/GCC.EXE crashes with SIGILL, hard.
Date:	Wed, 28 Mar 2012 20:26:03 -0500
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

>"Rugxulo" <rugxulo AT gmail DOT com> wrote in message 
>news:963ed3e2-354f-48ce-90fd->43fb7263fe2d AT v2g2000vbx DOT googlegroups DOT com...

>My question to anybody reading is this:  Can you trap SIGILL in a
>subprocess (spawned child .EXE) from a host parent .EXE?

Under DPMI 1.x, there is only one exception handler vector, so
either a parent process can monitor what the child processess are
doing, (or if the DPMI call hook isn't modified) a child can be the
last-in hook to handle.  This is how DJGPP debuggers work.

>In other words, how would you even fix this?

If you modify the library to monitor SIGILL and handle CMOV,
that would be one way.  You could also create a shell program
(like redir) that hooked the right signals, then hooked some
DPMI hooks to prevent the child from setting up it's own
SIGILL handler.  Catching and emulating will be slower.

>A binary patch might also be feasible and at least a good short-term
>ad hoc fix here, but CMOVxx is apparently smaller in opcode size than
>the CMP / Jxx alternative, so that makes things trickier. And I have
>not actively tried any of these methods (which is why I've delayed in
>responding publicly), but some feedback is probably beneficial.

There are ways to write binary patches that jump to a patch area,
execute, then jump back, but this is more complex.  Might be able
to identify dead "noop" space to steal, but once again lots of code to
write, test to "repair" a bug. 

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