View source for GDC/Cross Compiler/Existing Sysroot

{{ParentArticle|[[GDC]] > [[GDC/Cross Compiler|Cross Compiler]]}} 

This describes how to build or use a cross compiler if you have access to an existing system root (short sysroot). A sysroot is
a folder which contains a minimal filesystem (especially libraries, the C library and header files). An example sysroot could
look like this: 'sysroot/usr', 'sysroot/usr/lib', 'sysroot/usr/include'.

__TOC__

== The sysroot ==
We assume that a sysroot is available at $SYSROOT. If the sysroot directory is inside the
prefix where we'll install the compiler, the complete prefix directory can be moved to different
locations. If it's not in the prefix directory GCC always uses the absolute path for the sysroot and
if you move the sysroot the compiler will not work anymore.

=== Sysroot over SSH ===
If your target machine offers a fast SSH access it's possible to use the file system of the
remote machine directly. This way the crosscompiler has full access to all libraries of the
remote system. If a library is missing simply install it on the remote machine using the standard
package manager.

You can mount a remote sysroot by using SSHFS:
<syntaxhighlight lang="bash">
sshfs -o idmap=user,follow_symlinks user@targethost:/ $SYSROOT
</syntaxhighlight>
'''user@targethost''' is an SSH user / hostname account.
'''$SYSROOT''' is the location where the sysroot will be mounted.

The '''follow_symlinks''' option is important. The remote filesystem will have absolute symlinks (/usr/lib/libdl.so --> /usr/lib/libdl.so.2)
.'''follow_symlinks''' makes sure we really get access to the remote /usr/lib/libdl.so.2 and not to the local one.

== Using a compiler from gdcproject.org/downloads ==
You can use the compilers from http://gdcproject.org/downloads with a SSH sysroot,
but the system accessed over SSH must be similar to the system the cross-compilers
"emulate". For example ArchlinuxARM systems are known to work, debian systems will
not work (debian uses additional patches for binutils which were not compiled into 
the compilers from gdcproject.org).

To use such an compiler with the SSH sysroot, use the '--sysroot' switch:
<syntaxhighlight lang="bash">
./arm-gdcproject-linux-gnueabihf/bin/arm-gdcproject-linux-gnueabihf-gdc --sysroot=$SYSROOT test.d
</syntaxhighlight>

Now you can link with any library installed on the remote machine:
<syntaxhighlight lang="bash">
./arm-gdcproject-linux-gnueabihf/bin/arm-gdcproject-linux-gnueabihf-gdc --sysroot=$SYSROOT test.d -lcurl
</syntaxhighlight>

== Building a new compiler ==
=== Specifying a target and installation folder ===
<syntaxhighlight lang="bash">
export TARGET=arm-linux-gnueabi
export PREFIX={installation folder}
export SYSROOT={sysroot folder}
</syntaxhighlight>

Replace <code>{installation folder}</code> with the absolute path to the folder the toolchain should be installed in.

=== GNU Binutils ===
<syntaxhighlight lang="bash">
# Delete existing binutils source archive and download a new one
#-------------------------------------------------------------------
export BINUTILS_NAME=binutils-2.24
export BINUTILS_SOURCE_ARCHIVE=$BINUTILS_NAME.tar.bz2
rm -f $BINUTILS_SOURCE_ARCHIVE
rm -rf $BINUTILS_NAME
wget http://ftpmirror.gnu.org/binutils/$BINUTILS_SOURCE_ARCHIVE

# Extract binutils
#-------------------------------------------------------------------
tar xjfv $BINUTILS_SOURCE_ARCHIVE

# Create binutils build directory
#-------------------------------------------------------------------
export BINUTILS_BUILD_DIR=binutils-build
rm -rf $BINUTILS_BUILD_DIR
mkdir $BINUTILS_BUILD_DIR

# Configure and build binutils
#-------------------------------------------------------------------
cd $BINUTILS_BUILD_DIR
../$BINUTILS_NAME/configure \
  --with-sysroot=$SYSROOT \
  --target=$TARGET   \
  --prefix=$PREFIX   \
  --disable-nls      \
  --disable-multilib \
  --with-gnu-as      \
  --with-gnu-ld      \
  --disable-libssp   
make -j4 all
make install
cd ..
</syntaxhighlight>

==== Note: Debian targets ====
If you're target sysroot is a recent debian distribution (>= wheezy) you'll have to apply one of the debian patches to
binutils. Download it from here: http://bazaar.launchpad.net/~doko/binutils/pkg-2.24-debian/view/head:/patches/129_multiarch_libpath.patch

You then have to set '''DEB_TARGET_MULTIARCH''' before building binutils:
<syntaxhighlight lang="bash">
export DEB_TARGET_MULTIARCH=arm-linux-gnueabi
</syntaxhighlight>
The correct value can be obtained by executing this on the target:
<syntaxhighlight lang="bash">
dpkg-architecture -qDEB_HOST_MULTIARCH
</syntaxhighlight>

=== Download GDC ===
<syntaxhighlight lang="bash">
# Download GDC
#-------------------------------------------------------------------
rm -rf gdc
mkdir gdc
git clone https://github.com/D-Programming-GDC/GDC.git gdc
cd gdc
git checkout gdc-4.8
cd ..
</syntaxhighlight>

=== Download GCC ===
<syntaxhighlight lang="bash">
# Delete existing GCC source archive and download a new one
#-------------------------------------------------------------------
export GCC_NAME=gcc-4.8.2
export GCC_SOURCE_ARCHIVE=$GCC_NAME.tar.bz2
rm -f $GCC_SOURCE_ARCHIVE
rm -rf $GCC_NAME
wget http://ftp.tsukuba.wide.ad.jp/software/gcc/releases/$GCC_NAME/$GCC_SOURCE_ARCHIVE

# Extract GCC
#-------------------------------------------------------------------
tar xjfv $GCC_SOURCE_ARCHIVE
</syntaxhighlight>

=== Add GDC to GCC ===
<syntaxhighlight lang="bash">
# Add GDC to GCC
#-------------------------------------------------------------------
cd gdc
./setup-gcc.sh ../$GCC_NAME
cd ..
</syntaxhighlight>

=== Build GCC ===
<syntaxhighlight lang="bash">
# Create GCC build directory
#-------------------------------------------------------------------
export GCC_BUILD_DIR=gcc-build
rm -rf $GCC_BUILD_DIR
mkdir $GCC_BUILD_DIR

# Configure and build GCC
#-------------------------------------------------------------------
cd $GCC_BUILD_DIR
../$GCC_NAME/configure --target=$TARGET --prefix=$PREFIX \
  --enable-languages=d     \
  --disable-bootstrap      \
  --disable-libssp         \
  --disable-libgomp        \
  --disable-libmudflap     \
  --disable-multilib       \
  --disable-decimal-float  \
  --disable-libffi         \
  --disable-libmudflap     \
  --disable-libquadmath    \
  --disable-libssp         \
  --disable-nls            \
  --with-gnu-as            \
  --with-gnu-ld            \
  --with-sysroot=$SYSROOT
make -j4
make install
</syntaxhighlight>


[[Category:GDC Compiler]]