uKernel/doc/cross-gcc.md

Cross-compiling with GCC

Some compilers, like GCC, need to be built for a specific platform in order to compile code suitable there. This document gathers the different steps required for this purpose. Three major steps are required:

• install the dependencies
• compile binutils
• compile GCC

Dependencies

Binutils and GCC require the following software components to be available in the system prior to their installation:

Component	Notes
Make	eg GNU Make or BSD Make
Bison
Flex
GMP
MPC
MPFR
Texinfo

Please refer to the manual of your local system for information on how to find and install these components as required.

Binutils

Download the latest version of binutils; at the time of writing this document it is version 2.32:

$ wget https://ftpmirror.gnu.org/binutils/binutils-2.32.tar.gz

To configure binutils it is necessary to choose a target. It can be chosen according to the following table:

Port	Target
amd64	amd64-elf
i386	i686-elf

Modify the environment to reflect this choice; in this case for the i386 port:

$ TARGET="i686-elf"
$ PREFIX="$HOME/opt/cross-gcc-$TARGET"
$ PATH="$PREFIX/bin:$PATH"

Extract, configure, and build binutils in a dedicated tree:

$ tar xzf binutils-2.32.tar.gz
$ mkdir binutils-build
$ (cd binutils-build && ../binutils-2.32/configure --target="$TARGET" \
  --prefix="$PREFIX" --with-sysroot --disable-nls --disable-werror)
$ (cd binutils-build && make)
$ (cd binutils-build && make install)

GCC

Download the latest version of GCC; at the time of writing this document it is version 8.3.0:

$ wget https://ftpmirror.gnu.org/gcc/gcc-8.3.0/gcc-8.3.0.tar.gz

Just the same, GCC has to be configured for the target chosen.

Note: GNU Make is required to build GCC.

Extract, configure, and build GCC in a dedicated tree:

$ tar xzf gcc-8.3.0.tar.gz
$ mkdir gcc-build
$ (cd gcc-build && ../gcc-8.3.0/configure --target="$TARGET" \
  --prefix="$PREFIX" --disable-nls --enable-languages=c,c++ \
  --without-headers
$ (cd gcc-build && make all-gcc)
$ (cd gcc-build && make all-target-libgcc)
$ (cd gcc-build && make install-gcc)
$ (cd gcc-build && make install-target-libgcc)

Using the cross-compiler

Make sure the compiler binaries are available in your PATH:

$ export TARGET="i686-elf"
$ export PATH="$HOME/opt/cross-gcc-$TARGET/bin:$PATH"

The compiler can then be used directly. For instance, its version can be obtained by invoking the following:

$ $TARGET-gcc --version

Troubleshooting

In case the combination of binutils and GCC does not build together, it is possible to refer to the following table and choose a combination known to have worked before: https://wiki.osdev.org/Cross-Compiler_Successful_Builds