= Installing OCaml from sources on a Unix(-like) machine =

== Prerequisites

* A C compiler is required.

  ** For GNU/Linux +
   The GNU C Compiler (`gcc`) is recommended as the bytecode interpreter takes
   advantage of GCC-specific features to enhance performance. GCC is the standard
   compiler under Linux and many other systems.

  ** For BSDs +
   `clang` is the default C compiler on BSDs - also works fine.

  ** For macOS +
   `clang` is the default C compiler under macOS. If macOS complains
   no C compiler was installed while OCaml is building, please run
   command `xcode-select --install` to install command-line tools and
   required libraries and header files.

  ** For other Unix-like systems +
   It is recommended to use `gcc` or `clang` instead of the C compiler
   provided by the vendor of the system.

  ** For Windows +
   To produce native Windows executables from OCaml sources, you need to use
   the MSVC or MinGW-w64 ports of OCaml, described in file
   https://github.com/ocaml/ocaml/blob/trunk/README.win32.adoc[README.win32.adoc]. +
   For a more Unix-like experience, you can use WSL, the
   https://aka.ms/wsl[Windows Subsystem for Linux], or the
   https://www.cygwin.com/[Cygwin environment]. You will need the
   GCC compiler (package `gcc-core` or `gcc`).

* GNU `make`, as well as POSIX-compatible `awk` and `sed` are required.

* A POSIX-compatible `diff` is necessary to run the test suite.

* If you do not have write access to `/tmp`, you should set the environment
  variable `TMPDIR` to the name of some other temporary directory.

* The zstd library is used for compression of marshaled data. The option
  `--without-zstd` may be passed to `configure` in order to disable it.

== Prerequisites (special cases)

* Under Cygwin, the `gcc-core` package is required. `flexdll` is also necessary
  for shared library support.

* Binutils including `ar` and `strip` are required if your distribution
  does not already provide them with the C compiler.

== Configuration

From the top directory, do:

        ./configure

This generates the three configuration files `Makefile.config`,
`runtime/caml/m.h` and `runtime/caml/s.h`.

The `configure` script accepts options that can be discovered by running:

        ./configure --help

Some options or variables like LDLIBS may not be taken into account
by the OCaml build system at the moment. Please report an issue if you
discover such a variable or option and this causes troubles to you.

Examples:

* Standard installation in `/usr/{bin,lib,man}` instead of `/usr/local`:
    ./configure --prefix=/usr


* On a Linux x86-64 host, to build a 32-bit version of OCaml:

    ./configure --build=x86_64-pc-linux-gnu --host=i686-linux-gnu

* For AIX 7.x with the IBM compiler `xlc`:

    ./configure CC=xlc
+
By default, build is 32-bit. For 64-bit build, please set environment variable `OBJECT_MODE=64`
  for _both_ `configure` and `make world` phases. Note, if this variable is set for only one phase,
  your build will break (`ocamlrun` segfaults).
+
* For Solaris/Illumos on SPARC machines with Sun PRO compiler only 64-bit
  bytecode target is supported (32-bit fails due to alignment issues; the optimization
  is preset to `-O4` for inlining):

    ./configure CC="cc -m64"
+
If something goes wrong during the automatic configuration, or if the generated
files cause errors later on, then look at the template files:

        Makefile.config.in
        Makefile.build_config.in
        runtime/caml/m.h.in
        runtime/caml/s.h.in
+
for guidance on how to edit the generated files by hand.

== Building the compiler

From the top directory, do:

        make

This builds the OCaml compiler for the first time.  This phase is
fairly verbose; consider redirecting the output to a file:

        make > make.log 2>&1     # in sh
        make >& make.log         # in csh

== (Optional) Running the testsuite

To be sure everything works well, you can run the test suite
   that comes with the compiler. To do so, do:

        make tests

== Installing the compiler

You can now install the OCaml system. This will create the following commands
   (in the binary directory selected during autoconfiguration):

[width="70%",frame="topbot",cols="25%,75%"]
|===============================================================================
| `ocamlc`     | the batch bytecode compiler
| `ocamlopt`   | the batch native-code compiler (if supported)
| `ocamlrun`   | the runtime system for the bytecode compiler
| `ocamlyacc`  | the parser generator
| `ocamllex`   | the lexer generator
| `ocaml`      | the interactive, toplevel-based system
| `ocamlmktop` | a tool to make toplevel systems that integrate user-defined C
                 primitives and OCaml code
| `ocamldebug` | the source-level replay debugger
| `ocamldep`   | generator of "make" dependencies for OCaml sources
| `ocamldoc`   | the documentation generator
| `ocamlprof`  | the execution count profiler
| `ocamlcp`    | the bytecode compiler in profiling mode
|===============================================================================

From the top directory, become superuser and do:

        make install

Installation is complete. Time to clean up. From the toplevel directory,
   do:

        make clean

After installation, do *not* strip the `ocamldebug` executables.
   This is a mixed-mode executable (containing both compiled C
   code and OCaml bytecode) and stripping erases the bytecode!  Other
   executables such as `ocamlrun` can safely be stripped.

== If something goes wrong

Read the "common problems" and "machine-specific hints" section at the end of
this file.

Check the files `m.h` and `s.h` in `runtime/caml/`.
Wrong endianness or alignment constraints in `machine.h` will
immediately crash the bytecode interpreter.

If you get a "segmentation violation" signal, check the limits on the stack size
and data segment size (type `limit` under csh or `ulimit -a` under bash). Make
sure the limit on the stack size is at least 4M.

Try recompiling the runtime system with optimizations turned off (change
`OC_CFLAGS` in `runtime/Makefile`). The runtime system
contains some complex, atypical pieces of C code which can uncover bugs in
optimizing compilers.  Alternatively, try another C compiler (e.g. `gcc` instead
of the vendor-supplied `cc`).

You can also use the debug version of the runtime system which is
normally built and installed by default. Run the bytecode program
that causes troubles with `ocamlrund` rather than with `ocamlrun`.
This version of the runtime system contains lots of assertions
and sanity checks that could help you pinpoint the problem.

== Common problems

* The Makefiles assume that make executes commands by calling `/bin/sh`. They
  won't work if `/bin/csh` is called instead.  You may have to unset the `SHELL`
  environment variable, or set it to `/bin/sh`.

* On some systems, localization causes build problems.  You should try to set
  the C locale (`export LC_ALL=C`) before compiling if you have strange errors
  while compiling OCaml.

* In the unlikely case that a platform does not offer all C99 float operations
  that the runtime needs, a configuration error will result.  Users
  can work around this problem by calling `configure` with the flag
  `--enable-imprecise-c99-float-ops`.  This will enable simple but potentially
  imprecise implementations of C99 float operations.  Users with exacting
  requirements for mathematical accuracy, numerical precision, and proper
  handling of mathematical corner cases and error conditions may need to
  consider running their code on a platform with better C99 support.
