Sweden-Number/documentation/how-to-port

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What is this?
------------
This note is a short description of
* How to port Wine to your favourite operating system
* Why you probably shouldn't use "#ifdef MyOS"
* What to do instead.
This document does not say a thing about how to port Wine to non-386
operating systems, though. You would need a CPU emulator. Let's get
Wine into a better shape on 386 first, OK?
Why "#ifdef MyOS" is probably a mistake.
---------------------------------------
Operating systems change. Maybe yours doesn't have the "foo.h"
header, but maybe a future version will have it. If you want
to "#include <foo.h>", it doesn't matter what operating system
you are using; it only matters whether "foo.h" is there.
Furthermore, operating systems change names or "fork" into
several ones. An "#ifdef MyOs" will break over time.
If you use the feature of Autoconf, the Gnu auto-configuration
utility wisely, you will help future porters automatically
because your changes will test for _features_, not names of
operating systems. A feature can be many things:
* existance of a header file
* existance of a library function
* existance of libraries
* bugs in header files, library functions, the compiler, ...
* (you name it)
You will need Gnu Autoconf, which you can get from your
friendly Gnu mirror. This program takes Wine's "configure.in"
file and produces a "configure" shell script that users use to
configure Wine to their system.
There _are_ exceptions to the "avoid #ifdef MyOS" rule. Wine,
for example, needs the internals of the signal stack -- that
cannot easily be described in terms of features.
Let's now turn to specific porting problems and how to solve
them.
MyOS doesn't have the `foo.h' header!
------------------------------------
This first step is to make Autoconf check for this header.
In configure.in you add a segment like this in the section
that checks for header files (search for "header files"):
AC_CHECK_HEADER(foo.h, AC_DEFINE(HAVE_FOO_H))
If your operating system supports a header file with the
same contents but a different name, say bar.h, add a check
for that also.
Now you can change
#include <foo.h>
to
#ifdef HAVE_FOO_H
#include <foo.h>
#elif defined (HAVE_BAR_H)
#include <bat.h>
#endif
If your system doesn't have a corresponding header file even
though it has the library functions being used, you might
have to add an "#else" section to the conditional. Avoid
this if you can.
You will also need to add "#undef HAVE_FOO_H" (etc.) to
include/config.h.in
Finish up with "make configure" and "./configure".
MyOS doesn't have the `bar' function!
------------------------------------
A typical example of this is the `memmove'. To solve this
problem you would add `memmove' to the list of functions
that Autoconf checks for. In configure.in you search for
AC_CHECK_FUNCS and add `memmove'. (You will notice that
someone already did this for this particular function.)
Secondly, you will also need to add "#undef HAVE_BAR"
to include/config.h.in
The next step depends on the nature of the missing function.
Case 1: It's easy to write a complete implementation of the
function. (`memmove' belongs to this case.)
You add your implementation in misc/port.c surrounded by
"#ifndef HAVE_MEMMOVE" and "#endif".
You might have to add a prototype for your function. If so,
include/miscemu.h might be the place. Don't forget to protect
that definition by "#ifndef HAVE_MEMMOVE" and "#endif" also!
Case 2: A general implementation is hard, but Wine is only using
a special case.
An example is the various "wait" calls used in SIGNAL_child
from loader/signal.c. Here we have a multi-branch case on
features:
#ifdef HAVE_THIS
...
#elif defined (HAVE_THAT)
...
#elif defined (HAVE_SOMETHING_ELSE)
...
#endif
Note that this is very different from testing on operating
systems. If a new version of your operating systems comes
out and adds a new function, this code will magically start
using it.
Finish up with "make configure" and "./configure".