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At first, the idea of an i386 "cross" compiler under Linux seems strange. After all, you're already running Linux on a i386 compatible architecture. But the compiler is sometimes tied in misterious ways with the operating system it's running on (see for example this page for some possible symptoms). And after all, you want to use Newlib, not libc, and to customize your development environment as much as possible. This tutorial will show you how to do that.

DISCLAIMER: I'm by no means a specialist in the GCC/newlib/binutils compilation process. I'm sure that there are better ways to accomplish what I'm describing here, however I just wanted a quick and dirty way to build a toolchain, I have no intention in becoming too intimate with the build process. If you think that what I did is wrong, innacurate, or simply outrageously ugly, feel free to contact me and I'll make the necessary corrections. And of course, this tutorial comes without any guarantees whatsoever.

› Prerequisites

To build your toolchain you'll need:

a computer running Linux: I use Ubuntu 8.04, but any Linux will do as long as you know how to find the equivalent of "apt-get" for your distribution. I won't be going into details about this, google it and you'll sure find what you need. It is also assumed that the Linux system already has a "basic" native toolchain installed (gcc/make and related). This is true for Ubuntu after installation. Again, you might need to check your specific distribution.
GNU binutils: get it from here. At the moment of writing this, the latest versions is 2.18, which for some weird reason refuses to compile on my system, so I'm using 2.17 instead.
GCC: version 4.3.0 or newer is recommended. As I'm writing this, the latest GCC version is 4.3.1 which I'll be using for this tutorial. Download it from here after choosing a suitable mirror.
Newlib: as I'm writing this, the latest official Newlib version is 1.16.0. Download it from the Newlib FTP directory.
Also, the tutorial assumes that you're using bash as your shell. If you use something else, you might need to adjust some shell-specific commands.

Also, you need some support programs/libraries in order to compile the toolchain. To install them:

$ sudo apt-get install flex bison libgmp3-dev libmpfr-dev autoconf texinfo

Next, decide where you want to install your toolchain. They generally go in /usr/local/, so I'm going to assume /usr/local/cross-i686 for this tutorial. To save yourself some typing, set this path into a shell variable:

$ export TOOLPATH=/usr/local/cross-i686

› Step 1: binutils

This is the easiest step: unpack, configure, build.

$ tar -xvjf binutils-2.17.tar.bz2
$ cd binutils-2.17
$ mkdir build
$ cd build
$ ../configure --target=i686-elf --prefix=$TOOLPATH --with-gnu-as --with-gnu-ld --disable-nls
$ make all
$ sudo make install
$ export PATH=${TOOLPATH}/bin:$PATH

Now you have your i386 "binutils" (assembler, linker, disassembler ...) in your PATH.

› Step 2: basic GCC

In this step we build a "basic" GCC (that is, a GCC without any support libs, which we'll use in order to build all the libraries for our target). But first we need to make a slight modification in the configuration files. Out of the box, the GCC 4.3.1/newlib combo won't compile properly, giving a very weird "Link tests are not allowed after GCC_NO_EXECUTABLES" error. After a bit of googling, I found the solution for this:

$ tar -xvjf gcc-4.3.1.tar.bz2
$ cd gcc-4.3.1/libstdc++-v3
$ joe configure.ac

I'm using "joe" here as it's my favourite Linux text mode editor, you can use any other text editor. Now find the line which says "AC_LIBTOOL_DLOPEN" and comment it out by adding a "#" before it:

  # AC_LIBTOOL_DLOPEN

Save the modified file and exit the text editor

$ autoconf
$ cd ..

Great, now we know it will compile, so let's do it:

$ mkdir build
$ cd build
$ ../configure --target=i686-elf --prefix=$TOOLPATH --enable-languages="c,c++" --with-newlib --without-headers --disable-shared --with-gnu-as --with-gnu-ld
$ make all-gcc
$ sudo make install-gcc

On my system, the last line above (sudo make install-gcc) terminated with errors, because it was unable to find our newly compiled binutils. If this happens for any kind of "make install" command, this is a quick way to solve it:

$ sudo -s -H

  # export PATH=/usr/local/cross-i686/bin:$PATH
  # make install-gcc
  # exit

› Step 3: Newlib

Once again, Newlib is as easy as unpack, configure, build. But I wanted my library to be as small as possible (as opposed to as fast as possible) and I only wanted to keep what's needed from it in the final executable, so I added the "-ffunction-sections -fdata-sections" flags to allow the linker to perform dead code stripping:

$ tar xvfz newlib-1.16.0.tar.gz
$ cd newlib-1.16.0
$ mkdir build
$ cd build
$ ../configure --target=i686-elf --prefix=$TOOLPATH --disable-newlib-supplied-syscalls --with-gnu-ld --with-gnu-as --disable-shared
$ make CFLAGS_FOR_TARGET="-ffunction-sections -fdata-sections -D__PREFER_SIZE_OVER_SPEED -D__OPTIMIZE_SIZE__ -Os -fomit-frame-pointer -D__BUFSIZ__=256"
$ sudo make install

Some notes about the flags used in the above sequence:

--disable-newlib-supplied-syscalls: this deserves a page of its own, but I won't cover it here. For an explanation, see for example this page.
-D__PREFER_SIZE_OVER_SPEED -D__OPTIMIZE_SIZE__: compile Newlib for size, not for speed (these are Newlib specific).
-Os -fomit-frame-pointer: tell GCC to optimize for size, not for speed.
-D__BUFSIZ__=256: again Newlib specific, this is the buffer size allocated by default for files opened via fopen(). The default is 1024, which I find too much for an eLua, so I'm using 256 here. Of course, you can change this value.

› Step 4: full GCC

Finally, in the last step of our tutorial, we complete the GCC build. In this stage, a number of compiler support libraries are built (most notably libgcc.a). Fortunately this is simpler that the Newlib compilation step:

$ cd gcc-4.3.1/build
$ make all
$ sudo make install

› Step 5: all done!