Coredump Message Meanings - Summary - (nf)

[utzoo!decvax!harpo!npoiv!npois!houxm!ihnp4!ihldt!ll1!otuxa!nwuxc!inuxc!pur-ee!davy]

#N:pur-ee:15500007:000:3266
pur-ee!davy    Dec  6 11:05:00 1982



	This is the information which I have received in response to 
my query about the meanings of the various core dump messages given by 
the shell.  I have summarized much of the information in order to keep 
this article reasonably short (well, 100 lines is shorter than 300....).

------------------

	Bus Error
	    - Types of arguments and parameters don't match.
	    - I/O problems - reading past EOF, reading a closed
	      file, bad file pointers, etc.
		[This refers to stdio only, I think.... --Dave]
	    - Arrays improperly dimensioned.  Eg., attempting to 
	      access a word starting at an odd address.  
	    - Referencing a non-existent bus device.
	    - NULL or unitialized pointer, subscript out of range.

	Memory Fault
	    - Subscripting arrays past the memory allocation for 
	      your program.
	    - NULL or unitialized pointer, subscript out of range.
	    - Attempts to reference data outside valid address space
	    - Parity errors in address space
	    - Recursion (try making your own routines "read" and "write"
	      and then call "scanf" or "printf" and watch what happens).
	
	IOT Trap
	    - Execution of IOT (I/O Trap) instruction; also used by the 
	      "abort" routine (PDP-11's only).

	EMT Trap
	    - Emulator Trap Instruction (PDP-11's).

	Trace/BPT Trap
	    - Execution of the BPT instruction (PDP-11's)
	    - Trace bit set in Processor Status (long)Word
	    - Trying to tell the program to go to an address that
	      doesn't exist.
	    - "Wanton destruction caused execution of data or trashing
	      of instructions."
	    
	Floating Exception
	    - Invalid floating point operation:
		- overflow
		- underflow
		- divide by zero
		- log of negative number
		- float-to-int conversion overflow
	
	Segmentation Fault
	    - Subscript out of range.
	    - Handing "printf", etc. a string which is not NULL
	      terminated.

	Illegal Instruction
	    - Attempt to execute a priviledged instruction, such
	      as "halt".
	    - Execution of nonsense insstruction (e.g., jump to a
	      register).
	    - Forgot -f flag to cc on PDP-11 without floating point 
	      hardware.

	----- Special Note: John Bruner (pur-ee!bruner) also had this
	    to say about Illegal Instruction:

		"On the VAXes the 'abort' routine executes a 'halt' 
		and blows away the program with an illegal instruction.
		Note that SIGTRAP (trace trap) and SIGILL (illegal
		instruction trap) are not reset when caught.  Thus, a
		generalized trap handler such as

			sig(s)
			int s;
			{
			    fprintf(stderr, "Fatal signal %d\n", sig);
			    abort();
			}
		
		will (on the VAX) recursively call 'abort' which will 
		attempt to execute a 'halt' [illegal] and trap to 'sig'
		which will call 'abort'... until you either kill it 
		with a signal it doesn't catch (e.g. SIGKILL=9) or it
		runs out of stack space (a LONG time on the VAX)."
	

------------------

	In all, I got 5 responses with information about the messages,
and three responses asking for a copy of the summary (to those of you
who asked, I have sent you each a copy via mail).  Thanks go to all
who responded: John Bruner (pur-ee!bruner), arizona!tom, ihuxw!thor, 
Bob Van Valzah (tpdcvax!bobvan), Geoff Collyer (utcsstat!geoff).

--Dave Curry
pur-ee!davy