Building GCC and Binutils to target Theseus (x86_64-elf)

We provide a script that does all of this for you; see scripts/install_x86_64-elf-gcc.sh, 

./scripts/install_x86_64-elf-gcc.sh $HOME/src $HOME/opt

In this document, we refer to two directories, both of which can be set to the location of your choice:

  1. $SRC: the directory that contains the source for gcc and binutils
    • For example, $HOME/src/
  2. $DEST: the directory that will hold our compiled gcc and binutils packages and libraries (where they will be installed)
    • For example, $HOME/opt/

(Instructions were taken from this tutorial on the OS dev wiki.)

1. Build a standalone version of GCC & Binutils

Install the required packages:

sudo apt-get install gcc build-essential bison flex libgmp3-dev libmpc-dev libmpfr-dev texinfo gcc-multilib

Download and build GCC/Binutils

For this tutorial, we'll use gcc version 10.2.0, released July 20, 2020, and binutils version 2.35.1, released September 19, 2020.

You can obtain it from many mirrors online, such as these:

Create a destination directory for the newly-built packages to be installed into:

mkdir $DEST
export PREFIX="$DEST/gcc-10.2.0"

Extract each source code package into the directory of your choice ($SRC), and then build binutils:

mkdir build-binutils
cd build-binutils
../binutils-2.35.1/configure --prefix="$PREFIX" --disable-nls --disable-werror
make -j$(nproc)
make install

Then go back to the $SRC directory and build gcc:

# Use a GCC script to download all necessary prerequisites
cd gcc-10.2.0
./contrib/download_prerequisites
cd ../

mkdir build-gcc
cd build-gcc
../gcc-10.2.0/configure --prefix="$PREFIX" --disable-nls --enable-languages=c,c++
make -j$(nproc)
make install

2. Build GCC and Binutils again, to cross-target Theseus (x86_64-elf)

Now that we have a standalone build of gcc/binutils that is independent from the one installed by your host system's package manager, we can use that to build a version of gcc that inherently performs cross-compilation for a specific target, in this case, our Theseus x86_64-elf target.

Note: these instructions are based on this tutorial from the OS dev wiki.

First, create a directory for the cross compiler to be built and installed into, e.g., $DEST/cross.

mkdir $DEST/cross
export PREFIX="$DEST/cross"
export TARGET=x86_64-elf
export PATH="$PREFIX/bin:$PATH"

Second, re-build the same binutils package as above, but in a way that configures it to target Theseus. 

../binutils-2.35.1/configure --target=$TARGET --prefix="$PREFIX" --with-sysroot --disable-nls --disable-werror
make -j$(nproc)
make install

Confirm that your new cross-compiler binutils package exists and is on your system PATH:

which --$TARGET-as

should output something like:

/home/my_username/opt/cross/bin/x86_64-elf-as

Then go back to the $SRC directory and build a version of gcc that cross compiles C/C++ programs to Theseus.

mkdir cross-build-gcc
cd cross-build-gcc
../gcc-10.2.0/configure --target=$TARGET --prefix="$PREFIX" --disable-nls --enable-languages=c,c++ --without-headers
make all-gcc -j$(nproc)
make all-target-libgcc -j$(nproc) 
make install-gcc
make install-target-libgcc

Before moving on, let's check to make sure our cross-compiled gcc is working.

$DEST/cross/bin/$TARGET-gcc --version

This should print out some information about your newly-built gcc. Add the -v flag to dump out even more info.

3. Re-building GCC without the default red-zone usage

Importantly, we must disable the red zone in gcc entirely. When invoking gcc itself, we can simply pass the -mno-red-zone argument on the command line, but that doesn't affect the cross-compiled version of libgcc itself. Thus, in order to avoid libgcc functions invalidly using the non-existing red zone in Theseus, we have to build a no-red-zone version of libgcc in order to successfully build and link C programs for Theseus, without libgcc's methods trying to write to the red zone.

Note: instructions were adapted from this tutorial.

Adjusting the GCC config

First, create a new file within the gcc source tree at $SRC/gcc-10.2.0/gcc/config/i386.
Add the following lines to that new file and save it:

MULTILIB_OPTIONS += mno-red-zone
MULTILIB_DIRNAMES += no-red-zone

Yes, even though we're building for x86_64, we put it in the original x86 architecture config folder called i386.

Then, instruct gcc's build process to use that new multilib configuration. Open the file $SRC/gcc-10.2.0/gcc/config and search for the following configuration lines, which starts on Line 1867 (for gcc-10.2.0):

x86_64-*-elf*)
	tm_file="${tm_file} i386/unix.h i386/att.h dbxelf.h elfos.h newlib-stdint.h i386/i386elf.h i386/x86-64.h"
	;;

Add a line such that it looks like this:

x86_64-*-elf*)
	tmake_file="${tmake_file} i386/t-x86_64-elf"
	tm_file="${tm_file} i386/unix.h i386/att.h dbxelf.h elfos.h newlib-stdint.h i386/i386elf.h i386/x86-64.h"
	;;

Note: the indentation before tmake_file must be a TAB, not spaces.

Building GCC again with no red zone

Go back to the build directory and reconfigure and re-make libgcc:

cd $SRC/cross-build-gcc
../gcc-10.2.0/configure --target=$TARGET --prefix="$PREFIX" --disable-nls --enable-languages=c,c++ --without-headers
make all-gcc -j$(nproc)
make all-target-libgcc -j$(nproc) 
make install-gcc
make install-target-libgcc

To check that it worked, run the following two commands:

x86_64-elf-gcc -print-libgcc-file-name
x86_64-elf-gcc -mno-red-zone -print-libgcc-file-name

The first one should output a path to libgcc.a, and the second should output a similar path with no-red-zone as the containing directory:

$DEST/cross/lib/gcc/x86_64-elf/10.2.0/libgcc.a
$DEST/cross/lib/gcc/x86_64-elf/10.2.0/no-red-zone/libgcc.a

Appendix: How to use the no-red-zone version of GCC

To properly use this new version of GCC that cross-compiles to the Theseus target and disables the red zone, make sure you:

  1. use the x86_64-elf-gcc executable that now resides in $DEST/cross
  2. specify the -mno-red-zone flag, either on the command line or as part of LDFLAGS