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Add some docs about our compilers and patches done to them.

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Change-Id: I60e0960499aec789ae6240eec949249adb2e35ad
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5224
Reviewed-by: Fredrik Holmqvist <fredrik.holmqvist@gmail.com>
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PulkoMandy 2022-04-21 17:40:11 +02:00 committed by Fredrik Holmqvist
parent 323c6d6bce
commit b5ab38ecf0
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Haiku compilers
===============
For legacy reason, Haiku uses gcc2 to build parts of the system. This only applies to the x86 32bit
version of Haiku, which maintains binary compatibility with BeOS applications. The other ports of
Haiku are not affected by this, and use a more modern version of GCC (version 10 at the time of the
writing).
The compilers are available in the separate "buildtools" repository. This repository contains gcc
as well as the binutils (assembler, linker, etc). These are modified versions of the GNU tools, to
handle the specifics of Haiku. The gcc2 compiler is still getting some maintenance updates and
bugfixes. For the modern tools, the goal is to eventually re-integrate these changes into the
upstream version.
There is also work in progress to be able to build Haiku with llvm/clang as an alternative to gcc.
Summary of changes made to gcc for Haiku support
------------------------------------------------
This is an incomplete list of the changes.
- The -pthread option does nothing. In Haiku, pthreads are always enabled.
- The -fPIE option does the same thing as -fPIC. In Haiku, executables are also loadable as shared
libraries because they can be loaded using load_add_on for use as replicants. Using the standard
gcc implementation of -fPIE would then break, because it generates code that can't be used in a
shared library. For this reason, -fPIE in Haiku instead does the same thing as -fPIC.
- Header search path in Mac OS is case sensitive. Mac OS can handle both case sensitive and case
insensitive filesystems. Building Haiku requires a case sensitive filesystem, otherwise it's not
possible to tell apart headers like string.h and String.h. When compiling gcc for Mac OS, it
normally has code to force case insensitive comparison of header filenames, no matter what the
underlying filesystem offers. This is disabled in our version of gcc.

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The build system
================
Building a complete operating system is a somewhat complex task. Simple tools like GNU make would
result in a lot of problems and hard to maintain scripts if used this way.
Haiku uses a slightly more elaborate tool called Jam. Jam was initially developed by Perforce, but
they have now abandoned the product. As a result, Haiku currently maintains its own fork of Jam
with several customizations.
The core idea of Jam is to provide generic rules (for example "how to build an application from a set
of source files") and then apply these rules several times. The Haiku build system defines a number
of custom rules, allowing to build code both for Haiku and for the host operating system (to be run
during the compiling process).
The build system also offers various ways to configure and customize your Haiku disk image.
.. toctree::
/build/compilers
/build/repositories/README

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:maxdepth: 2
:caption: Contents:
/build/repositories/README
/build/index
/apps/haikudepot/server
/midi/index
/net/NetworkStackOverview