Here's a first draft of instructions for cross-building a GCC/EGLIBC
pair. Criticism welcome, and actively solicited.
Cross-Compiling EGLIBC
Jim Blandy <jimb@xxxxxxxxxxxxxxxx>
Introduction
Most GNU tools have a simple build procedure: you run their
'configure' script, and then you run 'make'. Unfortunately, the
process of cross-compiling the GNU C library is quite a bit more
involved:
1) Build a cross-compiler, with certain facilities disabled.
2) Configure the C library using the compiler you built in step 1).
Build a few of the C run-time object files, but not the rest of the
library. Install the library's header files and the run-time
object files, and create a dummy libc.so.
3) Build a second cross-compiler, using the header files and object
files you installed in step 2.
4) Configure, build, and install a fresh C library, using the compiler
built in step 3.
5) Build a third cross-compiler, based on the C library built in step 4.
The reason for this complexity is that, although GCC and the GNU C
library are distributed separately, they are not actually independent
of each other: GCC requires the C library's headers and some object
files to compile its own libraries, while the C library depends on
GCC's libraries. EGLIBC includes features and bug fixes to the stock
GNU C library that simplify this process, but the fundamental
interdependency stands.
In this document, we explain how to cross-compile an EGLIBC/GCC pair
from source. Our intended audience is developers who are already
familiar with the GNU toolchain and comfortable working with
cross-development tools. While we do present a worked example to
accompany the explanation, for clarity's sake we do not cover many of
the options available to cross-toolchain users.
Preparation
EGLIBC requires recent versions of the GNU binutils and GCC. The web
page <http://www.eglibc.org/prerequisites> documents the current
requirements, and lists patches needed for certain target
architectures. In the example build process shown here we use
binutils 2.17 and GDB 4.1, which were current as we wrote this.
First, let's set some variables, to simplify later commands. We'll
build EGLIBC and GCC for a PowerPC target, known to the Linux kernel
as 'powerpc', and we'll do the build on an Intel Linux box:
$ build=i686-pc-linux-gnu
$ host=$build
$ target=powerpc-none-linux-gnu
$ linux_arch=powerpc
We're using the aforementioned versions of Binutils and GCC, and Linux
2.6.20:
$ binutilsv=binutils-2.17
$ gccv=gcc-4.1.1
$ linuxv=linux-2.6.20
And we're carrying out the entire process under '~/cross-build', which
contains unpacked source trees:
$ top=$HOME/cross-build/ppc
$ src=$top/src
$ ls $src
binutils-2.17 gcc-4.1.1 libc linux-2.6.20
$
Binutils
Configuring and building binutils for the target is straightforward.
However, since we're going to install it in several places, we leave
that step for later:
$ mkdir -p "$top/binutils/build"
$ cd $top/binutils/build
$ $src/$binutilsv/configure --target=$target --prefix=$top/bad-binutils
$ make
The First GCC
For our work, we need a cross-compiler targeting a PowerPC Linux
system. However, that configuration includes the shared library
'libgcc_s.so', which is compiled against the EGLIBC headers (which we
haven't installed yet) and linked against 'libc.so' (which we haven't
built yet).
Fortunately, there are configuration options for GCC which tell it not
to build 'libgcc_s.so'. The '--without-headers' option is supposed to
take care of this, but its implementation is incomplete, so you must
also configure with the '--with-newlib' option. While '--with-newlib'
appears to mean "Use the Newlib C library", its effect is to tell the
GCC build machinery, "Don't assume there is a C library available."
We also need to disable some of the libraries that would normally be
built along with GCC, and specify that only the C compiler is needed.
We'll build and install this first compiler in its own directory,
'$top/gcc1'. First, we install binutils there:
$ cd $top/binutils/build
$ make install prefix=$top/gcc1
Then, we configure, make, and install:
$ mkdir -p $top/gcc1/build
$ cd $top/gcc1/build
$ $src/$gccv/configure \
> --target=$target \
> --prefix=$top/gcc1 \
> --disable-shared --disable-threads --disable-libssp \
> --disable-libgomp --disable-libmudflap \
> --without-headers --with-newlib \
> --enable-languages=c
$ PATH=$top/gcc1/bin:$PATH make
$ PATH=$top/gcc1/bin:$PATH make install
Linux Kernel Headers
Before we can configure EGLIBC, we also need Linux kernel headers in
place. Fortunately, the Linux makefiles have a target that installs
them for us. Since the process does modify the source tree a bit, we
make a copy first:
$ mkdir -p "$top/linux"
$ cp -r $src/$linuxv $top/linux/build
$ cd $top/linux/build
Now we're ready to install the headers into the tree we'll be using
for the final toolchain, '$top/phase2':
$ phase2=$top/phase2
$ PATH=$top/gcc1/bin:$PATH \
> make headers_install \
> ARCH=$linux_arch CROSS_COMPILE=$target- \
> INSTALL_HDR_PATH=$phase2/$target