Why OCaml 4.07.1 gives almost identical backtrace in case of exception? ERROR: Writing file from Bigarray failed! ERROR: (Unix.Unix_error "Permission denied" map_file "") Raised at file "format.ml" (inlined), line 242, characters 35-52 Called from file "format.ml", line 469, characters 8-33 Called …

I just discussed this issue with XVilka on IRC and wish to set the record for those finding this page by google :slight_smile: , and it seems the key here is that Printexc.get_backtrace () should be the first thing done in the exception handler. Exn.to_string clobbers this value. Also a small corre…

Oh, nevermind, found: How to get useful backtraces? Why are exception backtraces global?

I added (flags (-g)) (link_flags (... -g)) in my dune file and ran the binary with OCAMLRUNPARAM=b set, but backtrace is still the same.

The problem is that Format catches and reraises the exception polluting the backtrace along the way. This is behavior should be fixed in 4.08.0 where Format uses raise_notrace to avoid this very issue.

As an aside, dune already defaults to compiling with -g ( source ). Also, OCAMLRUNPARAM is only evaluated by the bytecode versions, not the native binary.

Yes, I figured later that dune builds with symbols by default. Good to know the environment variable doesn’t work in the native mode.

OCaml and backtraces

Learning

XVilka March 21, 2019, 10:52am 2

Oh, nevermind, found:

How to get useful backtraces?
Why are exception backtraces global?

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OCaml and backtraces

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