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I'm trying to build the examples at https://github.com/mirage/mirage-tcpip in the folder "examples".

First I did opam install . in the root directory to install all dependencies. Then I did dune build and it build everything in _build, lots of .a, .cma, .cmx, .cmi, .cmxa files that I don't know what are for (can somebody explain?).

Anyways, I think the examples have to be built separately, because they have their own dune files. But I tried running dune build on them and got: 

root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# dune build
Entering directory '/workspaces/ocaml_env/mirage-tcpip'
root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# ls
dune  ping.ml
root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# cat dune 
(executables
 (names ping)
 (libraries cmdliner logs logs.fmt tcpip.icmpv4-socket))
root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# dune build ping
Entering directory '/workspaces/ocaml_env/mirage-tcpip'
Error: Don't know how to build ping
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1 Answers1

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Explanation of OCaml file types:

Regarding the file types in the _build directory (reference 1, reference 2):

  • .a are standard archive files (also known as static libraries) containing native code:

    Arguments ending in .o or .a (.obj or .lib under Windows) are assumed to be C object files and libraries. They are passed to the C linker when linking in -custom mode (see the description of -custom below).

  • .cma are the OCaml byte code equivalent of .a files, so static libraries, but with platform-independent OCaml byte code instead of machine-dependent native code:

    Arguments ending in .cma are taken to be libraries of object bytecode. A library of object bytecode packs in a single file a set of object bytecode files (.cmo files).

  • .cmx contain meta-data for how to link native code object files together:

    Arguments ending in .ml are taken to be source files for compilation unit implementations. ... From the file x.ml, the ocamlopt compiler produces two files: x.o, containing native object code, and x.cmx, containing extra information for linking and optimization of the clients of the unit.

  • .cmi are compiled interface definition files:

    Arguments ending in .mli are taken to be source files for compilation unit interfaces. Interfaces specify the names exported by compilation units: they declare value names with their types, define public data types, declare abstract data types, and so on. From the file x.mli, the ocamlopt compiler produces a compiled interface in the file x.cmi.

  • .cmxa are native code library files that combine .a/.o and and .cmx files, so like .a but with additional linking information from the .cmx files:

    Arguments ending in .cmxa are taken to be libraries of object code.

Building the example

Regarding the build of the ping example, to build an executable target with dune, you have to append .exe to the target name (reference):

Note that native code executables will have the .exe extension on all platforms (including non-Windows systems).

So the full sequence of build commands would be:

  • Install dependencies:

    $ opam install .

  • Build mirage-tcpip:

    $ dune build

  • Build the ping example:

    $ cd example/ping
$ dune build ping.exe

  • Run the binary:

    # dune exec ./ping.exe 8.8.8.8

    Alternatively, from the mirage-tcpip directory:

    # ./_build/default/examples/ping/ping.exe 8.8.8.8
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