[M3devel] Internal debugging - a simple design

[Hendrik Boom]

On Wed, Apr 03, 2013 at 12:45:23AM +0000, Jay K wrote:
>   Again, though, I don't want to change and recompile anything to debug.

Then an interpreter could be your friend.

> The idea is to debug w/o source and compiler.But it is a slippery 
> slope. Full "internal debugging" puts "almost" the source in the 
> executable.Is source absent because it is secret? or large? Or always 
> present?

The old Algol W compiler on the IBM 360 could be asked to place a 
trimmed-down copy of the source code somewhere (in memory if I recall 
correctly).  It would contain bytecodes for reserved words and 
operators, indexes into a symbol table for identifiers, and the like.
Then every time execution would enter a basic block, it would increment 
a counter -- one counter for each basic block.  When execution finished, 
it would prepare a printout, expanding all those brief byte codes and 
indices, indenting properly, and printing the count beside the start of 
every basic block.  I would debug from this listing and suppress the 
usual source-code listing.  This count-annotated listing was much more 
useful.

-- hendrik