Selective branch tracing enhancement

[Fish-Git]

This is the formal enhancement request originally made in another unrelated issue.

What is requested is a new instruction tracing feature that provides the ability to only trace branches that occur within a given address range , and, optionally, whose branch target is within a given address range (where the target range can optionally be specified as either the same range or a completely different range).

For example: given the pseudo-program segment:

    1            LTR   R5,R5
    2            BZ    SKIP
    3            L     R15,ASYS1
    4            BASR  R14,R15      Call system function
    5   SKIP     CLR   R6,R7
    6            BH    ERROR
    7            ...
    8            ...
    9   ERROR    BAS   14,MYMSGSUB
    10           ...
    11           ...
    12  MYMSGSUB ST    R14,SAVE14
    13           ...
    14           L     R15,IOFUNC
    15           BASR  R14,R15      Call system function
    16           ...
    17           L     R14,SAVE14
    18           BR    R14

What is desired is the ability to specify e.g. t+ branches 1-11 into same, which would only trace the branches at 2 and 6, but not the branches at 4 (target outside of range) or 9 (same reason: target outside of range) or 15 (branch instruction itself outside of range) or 18 (same reason: branch instruction itself outside of range).

This GitHub Issue is being created to simply formalize the request since it was originally made in a different issue regarding a different matter.

[Fish-Git]

FYI:

Page 131 of IBM reference manual SC24-6334-73 "z/VM 7.3 Virtual Machine Operation" documents z/VM's own powerful tracing ability, including its own trace branch command that supports the ability to not only trace branches but also ones which optionally only occur within a specified address range and/or which branch into a given range, which coincidentally happens to be exactly the type of Hercules tracing support being requested by this GitHub Issue!

trace branch
trace branch into 10000-11000
trace branch from 24000-30000
trace branch into 10000-11000 from 24000-30000

Which, when translated to Hercules syntax, would be:

t+ branch
t+ branch into 10000-11000
t+ branch 24000-30000
t+ branch 24000-30000 into 10000-11000

I'm only mentioning this as a helpful hint of a possible alternative way of accomplishing your goal until such time as we can manage to provide the same/similar ability in Hercules.