Original bug ID: 6199
Reporter: @alainfrisch
Status: confirmed (set by @damiendoligez on 2014-06-04T20:05:23Z)
Resolution: open
Priority: normal
Severity: feature
Category: configure and build/install
Monitored by: @gasche

Bug description

ocamlc generates bytecode executable starting with a header in charge of launching ocamlrun. Under Unix, this is a simple #! header (containing the absolute path of ocamlrun) and under Windows, this is an ad hoc program obtained from stdlib/header.c. This creates some issues:

• Bootstrapping the compiler produces ocamlc/ocamllex executables (stored in the SVN) which depend on the machine where bootstrapping was done. Simply bootstrapping the same version on two different working copies will give different results.

• The header encourages to not call ocamlrun explicitly, but this makes it difficult to provide a relocatable binary distribution of the toolchain, or simply to distribute a bytecode executable (if not compiled with -custom, we really need to call ocamlrun anyway).

• Under Windows, the header is not tiny (about 223kB). (Arguably, we don't really care.) More importantly, maybe, is that calling a bytecode executable with the header creates two Windows processes, while using ocamlrun explicitly creates only one.

I propose to add a link-time flag to ocamlc to avoid inserting an header in the resulting program (and probably stop setting its executable flag). Or maybe this could simply be a special value for use_runtime. We would then use this flag so that the bootstrap tools (boot/ocamlc, boot/ocamllex) don't contain this header.

This will not fix the idempotency problem completely (because some local configuration values are hardcoded in config.ml), but it will be a good step in this direction. Having real idempotency of the bootstrap procedure would allow a nice application: checking in a CI server that the bootstrap fixpoint is reached in the SVN.