Portability of OCaml bytecode

Question

I compile an OCaml program in bytecode on an x86 machine, and transfer the bytecode to a ppc64 machine. Assuming that the ppc64 machine has ocamlrun (compiled for ppc64), will I be able to execute my program on the ppc64 architecture ? Is it that simple ?

In other terms, is the bytecode resistant to endianness ?

If not, then what is the purpose of the bytecode ?

Answer 1

I assume you don't need any external function; otherwise of course you need the binary code providing them.

Yes, the bytecode is resistant to endianness (and to word size), for systems supported by Ocaml.

^{(however, your bytecode may depend upon the particular version of ocamlrun interpreter and the Pervasives module used by your program; hence, a bytecode for Ocaml 4.01 might not run in Ocaml 4.02 runtime or vice versa; YMMV)}

In particular when you build Ocaml from its source code, it is compiling itself with a distributed version (in boot/ subdirectory ...) of ocamlc - which is a bytecode file.

And Ocaml folks badly need that portability, since most of the Ocaml compiler is written in Ocaml itself and is bootstrapped.

See also J.Pitrat's blog on meta-bugs, curse of the bootstrap which indirectly explains why updating that boot/ocamlc file has to be done rarely and carefully by Ocaml team. Within the Ocaml code, make bootstrap has to be done occasionally and very carefully (at least to commit a newer version of boot/ocamlc bytecode file).