Allow dune exec underneath perf rather than having to specify a target from _build.

[gs0510]

Currently the perf runs on dune exec rather than the binary, it would be nice to have dune allowing a perf with dune exec rather than having to specify the target from _build.

[avsm]

Would you be able to paste the command line that you currently use to run perf with a dune-built library?

[gs0510]

I currently run:

 perf record --call-graph dwarf _build/default/bench/main.exe -g

[avsm]

Thanks! So what we're looking for here is some dune mechanism to prefix a dune exec with another command. This might also help with running valgrind under a dune exec as well.

[ghost]

What about dune exec perf record --call-graph dwarf _build/default/bench/main.exe -g?

[gs0510]

@diml dune exec perf record --call-graph dwarf _build/default/bench/main.exe -g doesn't work because:

1. dune doesn't have the --call-graph or the -g flags.
2. dune exec after perf record has already ran so dune errors out.

[ghost]

Ah yes, there is a missing --. What about: dune exec -- perf record --call-graph dwarf _build/default/bench/main.exe -g?

[gs0510]

This works perfectly! I wonder if there's any use of dune exec -- here though since the remainder gives the same result?

[ghost]

ah yes, that's true actually. BTW, one other option is to add a (promote (until-clean)) field to your executable stanza. Dune will then copy it to the source directory

[gs0510]

perf works perfectly with binary in the source directory with (promote (until-clean)).

IMO what would be desirable is a way for running perf with dune exec or suffixing any such command with dune exec