[Soot-list] Counting exits in a loop - understanding Jimple "goto [?= nop]"

[David Given]

John Dean wrote:
[...]
> You say "When you operating at runtime, the targets of the goto instructions
> will be two disctinct Units." So for the "goto nop" that shows up in my list
> of statements, what are the "targets," that are "two distinct Units"?
> Likewise, for the "goto [?= nop]" statement: What are the "targets," that
> are "two distinct Units"?

You're being misled by the way it's being printed --- I ran into this
with cowjac.

Each body is a graph of statements. The goto statement's target is just
another statement. The naive way to turn a goto instruction to a string
just prints 'goto' followed by the string value of the target statement.

So 'goto nop' is appearing because the target of the goto is a nop
instruction *which is somewhere else in the graph*.

When you actually do this for real, then instead of just turning the
goto's target into a string you want to generate a label reference
instead. The pseudocode something like this:

when generating code for a goto:
  print "goto "
  print label for goto's target statement

for all statements in method body
  does this statement need a label?
    print label for statement
  generate code for statement

The code Soot uses to emit Jimple, which does this, is here:

https://github.com/Sable/soot/blob/master/src/soot/Printer.java
...in the printStatementsInBody() method.

(What would actually be kinda nice is a soot postprocessing phase that
walked the instruction graph and added label tags to each Unit; this
area is a bit counterintuitive...)

-- 
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