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debugging.md

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Debugging from Coq toplevel using Caml trace mechanism

  1. Launch bytecode version of Coq (coqtop.byte)
  2. Access Ocaml toplevel using vernacular command 'Drop.'
  3. Install load paths and pretty printers for terms, idents, ... using Ocaml command '#use "base_include";;' (use '#use "include";;' for installing the advanced term pretty printers)
  4. Use #trace to tell which function(s) to trace
  5. Go back to Coq toplevel with 'go();;'
  6. Test your Coq command and observe the result of tracing your functions
  7. Freely switch from Coq to Ocaml toplevels with 'Drop.' and 'go();;'

You can avoid typing #use "include" (or "base_include") after Drop by adding the following lines in your $HOME/.ocamlinit :

if Filename.basename Sys.argv.(0) = "coqtop.byte" then ignore (Toploop.use_silently Format.std_formatter "include")

Hints: To remove high-level pretty-printing features (coercions, notations, ...), use "Set Printing All". It will affect the #trace printers too.

Debugging from Caml debugger

Requires Tuareg mode in Emacs.
Coq must be configured with -local (./configure -local) and the byte-code version of coqtop must have been generated with make byte.

  1. M-x camldebug
  2. give the binary name bin/coqtop.byte
  3. give ../dev/ocamldebug-coq
  4. source db (to get pretty-printers)
  5. add breakpoints with C-x C-a C-b from the buffer displaying the ocaml source
  6. get more help from ocamldebug manual run step back start next last print x (abbreviated into p x) ...
  7. some hints:
  • To debug a failure/error/anomaly, add a breakpoint in Vernac.vernac_com at the with clause of the "try ... interp com with ..." block, then go "back" a few steps to find where the failure/error/anomaly has been raised
  • Alternatively, for an error or an anomaly, add breakpoints in the middle
    of each of error* functions or anomaly* functions in lib/util.ml
  • If "source db" fails, do a "make printers" and try again (it should build top_printers.cmo and the core cma files).
  • If you have the OCAMLRUNPARAM environment variable set, Coq may hang on startup when run from the debugger. If this happens, unset the variable, re-start Emacs, and run the debugger again.

Global gprof-based profiling

Coq must be configured with option -profile

  1. Run native Coq which must end normally (use Quit or option -batch)
  2. gprof ./coqtop gmon.out

Per function profiling

To profile function foo in file bar.ml, add the following lines, just after the definition of the function:

 let fookey = Profile.declare_profile "foo";;
 let foo a b c = Profile.profile3 fookey foo a b c;;

where foo is assumed to have three arguments (adapt using Profile.profile1, Profile. profile2, etc).

This has the effect to cumulate the time passed in foo under a line of name "foo" which is displayed at the time coqtop exits.