tracing and debugging

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Leopold Toetsch

May 27, 2005, 11:12:19 AM5/27/05
to Perl 6 Internals
Parrot's capabalities are increasing steadily, programs written for
Parrot especially those emitted from compilers are getting bigger and
Debugging Parrot programs didn't keep up with the pace and is becoming a

Some notes.

*) tracing or debugging an interpreter shall not influence that debugee.

This implies that any code executed during tracing or debugging is run
in a distinct interpreter. [1] [2]
This leads to some questions of how we created interpreter clones or
better: which interpreter vars and structures are how global. [3]

*) we should have distinct trace flag options, e.g.

--trace HLL_src | PIR_src | opcodes | subroutines

*) getting HLL source into Parrot

This is basically the same scheme as used for PASM/PIR source code.
- the lexer parses #line "file" comments
- this info is stored in a 2nd debug segment

*) src/debug.c and ops/debug.ops

I don't think that we should reinvent wheels and have a separate command
language for debugging (e.g. PDB_cond). Instead I'm in favor of having
just one opcode: debug_break and a Debugger PMC with methods to get e.g.
register contents/lexicals/globals from the debugee. E.g. a conditional
break point hook:

# break if I5 == 5
.sub break_i5 method
i = getattribute self, "debugee"
$I0 = self."get_reg"(i, "I5")
unless $I0 == 5 goto cont
cc = getattribute self, "cont" # invoke return continuation in debugee

*) pdb - the interactive debugger [4]

pdb is basically unmaintained, buggy and outdated.


[1] e.g. trace_op_dump uses PIO_eprintf which allocates mainly STRING*
resources which changes DOD/GC counts of the interpreter. This can lead
to the execution of different code paths and thus influences the running

[2] see USE_TRACE_DEBUG in src/runops_cores.c

[3] src/global_setup.c:init_world()

[4] make world or make pdb

Leopold Toetsch

May 27, 2005, 11:28:30 AM5/27/05
to Leopold Toetsch, Perl 6 Internals
Leopold Toetsch wrote:

> [2] see USE_TRACE_DEBUG in src/runops_cores.c



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