From:	"Lawrence Rust" <lvr AT nospam DOT softsystem DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	SIGALRM signal handler doesn't save FPU state
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Date:	Mon, 9 Sep 2002 22:10:40 +0100
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

I have a program that uses setitimer to raise periodic SIGALRM signals.  The
ANSI C/C++ spec guarantees very little about what can be done in a signal
handler.  However, I've discovered that djgpp 2.03 / gcc 3.10 don't
save/restore the FPU state across an async signal handler.  Consequently if
the foreground and the signal handler both execute simple floating points
ops (like multiply) then the foreground routine can be trashed.

I've added some inline assembler (fnsave/frstor) around my signal handler to
solve this.  Perhaps the FAQ could be updated to include this info or even
better if libc could include this for async signals.

-- Lawrence Rust, Software Systems, www.softsystem.co.uk
The problem with Windows XP: http://www.arachnoid.com/boycott

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