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From: tim@proton.amd.com (Tim Olson)
Newsgroups: comp.unix.questions
Subject: Re: Signals
Message-ID: <1991Feb21.022020.2357@mozart.amd.com>
Date: 21 Feb 91 02:20:20 GMT
References: <1991Feb20.153845.14999@b11.ingr.com>
Sender: usenet@mozart.amd.com (Usenet News)
Reply-To: tim@amd.com (Tim Olson)
Organization: Advanced Micro Devices, Austin, TX
Lines: 31

In article <1991Feb20.153845.14999@b11.ingr.com> dclark@b11.ingr.com (Dave Clark) writes:
| 
| When debugging a program recently, I found that it was crashing due to receipt
| of a signal "SIGEMT."  My manual describes this as:
| 
| 	SIGEMT		07	EMT instruction
| 
| Naturally, "EMT" is not defined anywhere else in the manual.  Can someone out
| there in netland tell me what EMT stands for?

On the PDP-11 processor, the EMT (Emulator Trap) instructions were
opcodes 0104000 - 0104377 that simply caused a specific trap to occur
when executed.  They were presumably to be used for emulating other
instructions not included in the standard instruction set.  The UNIX
kernel for the PDP-11 generated a SIGEMT signal when this trap
occured.

That's what the original "EMT" stands for, but what causes it in your
system is a different matter (and subject to the actual
implementation).  It is often used as the signal generated for
non-floating point arithmetic exceptions (e.g. overflow), since there
usually is no other standard signal for these.  For example, SunOS
generates a SIGEMT when a taddcctv instruction (tagged add, set
condition codes, trap overflow) overflows.



--
	-- Tim Olson
	Advanced Micro Devices
	(tim@amd.com)