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Program Trace Routine
In demand mode, the caller has control and can examine the program environment. No
distinction is made between fatal and nonfatal contingencies in demand mode. Note
that it is the caller's responsibility to clear registers in case of arithmetic fault and to
respond to the onsite operator in case of a II keyin. For interrupt guard mode (IGDM),
the trapped address may or may not be the address of the offending instruction.
Contingency interception can be reset with the following:
SLJ SNCLR$
In frequently executed code, the caller may not want to trace every iteration of a loop or
every call of a subroutine. A bug may not appear until a routine executes a number of
times. The following calling sequence provides a way to call SNOOPY selectively.
SLJ TCNT$
+ count,start
+ until,every
+ mode-bits,termination-address
where mode-bits and termination-address are the same as for an SLJ to SNOOPY.
The count field should be zero initially; it is incremented on each pass through the code.
If start ≤ count < until and (count - start)///every = 0 or (count - start) modulo every = 0,
SNOOPY begins tracing following the mode word. Otherwise, execution will continue in
normal (untraced) mode.
24.4.2. Demand Mode Commands
These are the SNOOPY commands, their permissible abbreviations, and their functions.
ABSAD (ABS, A)
Converts relative program addresses to absolute addresses. The parameters are
eltname,loc-counter,location.
or
symbol*
If the program is segmented and the specified address is in a segment not in main
storage, a message is printed.
In case of symbols, the Collector may look up only referenced symbols defined by
non-SYS$*RLIB$ routines unless the collection source code includes a
“TYPE EXTDIAG” statement. In this case, the Collector may search for all symbols
(see the Collector Programming Reference Manual).
This command is useful in conjunction with the BREAK, CAPTUR, CHANGE, DUMP,
JUMP, and TRAP commands.
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