Revision as of 08:24, 23 March 2012

The most straightforward way to use Scratchbox2 is within the Mer Platform SDK. This page will go through the steps of using SB2 to compile a simple program.

Prerequisites

• A properly setup SDK
• Scratchbox2 pre-installed (see SB2 Installation if not)
• Your home directory is in /home/<username> (otherwise see directory mappings)

Create a simple C program

We'll use ~/src/hello.c as the location of our code.

mkdir ~/src
cat <<EOF >~/src/hello.c
#include <stdio.h>
int main(int argc, char **argv)
{
   printf("Hello World\n");
   return 0;
}
EOF

And now to compile it:

sb2 gcc ~/src/hello.c -o ~/src/hello

This gets:

 sb2: Error: Invalid target specified, aborting.

When sb2 runs it needs to know where to get header files and libraries and what architecture and cross-compiler to use. This is called a 'target'. SB2 can be configured to run against multiple named targets.

SB2 Setup

Target Preparation

A target is a rootfs that contains development files like headers, libraries and possibly programs. Notably it does *not* need to contain compilers, linkers etc.

Still running in the sdk we'll create a target in the recommended /srv/mer/targets/ area.

sudo mkdir -p /parentroot/srv/mer/targets
sudo chown -R $USER /parentroot/srv/mer/targets

Now we need a kickstart file and then we can use mic to create the target

 cd /tmp
 curl -O http://releases.merproject.org/releases/0.20120315.1/kickstarts/mer-core-armv7hl-xorg-basic-qmlviewer.ks
 sudo mic create fs mer-core-armv7hl-xorg-basic-qmlviewer.ks -o /parentroot/srv/mer/targets --pkgmgr=yum --arch armv7hl

(Note: if you use a kickstart with @BUILD_ID@ and use the --release= option to mic then mic creates a slightly different structure and your rootfs will end up in /parentroot/srv/mer/targets/<release>/images/<name> and you'll have to move it)

The final step is to make sure the rootfs is all owned by the user. SB2 uses fakeroot when needed and won't work if the target has root-owned files.

 sudo chown -R $USER /parentroot/srv/mer/targets/*

This target could be any suitable rootfs such as a Nemo or PA rootfs.

Target Setup

To tell SB2 about the target we use sb2-init.

IMPORTANT : You must change directory to the target rootfs before running sb2-init.

 cd /parentroot/srv/mer/targets/mer-core-armv7hl-xorg-basic-qmlviewer
 sb2-init -d -L "--sysroot=/" -C "--sysroot=/" -c /usr/bin/qemu-arm-dynamic -m sdk-build -n -N -t / mer-core /opt/cross/bin/armv7hl-meego-linux-gnueabi-gcc

We now need to work around bug #238:

 echo -n "armv7hl-meego-linux" > etc/rpm/platform

And prepare the target for installation (all these steps will eventually be handled by a target preparation script or similar):

 sb2 -t mer-core -m sdk-install -R rpm --rebuilddb
 sb2 -t mer-core -m sdk-install -R zypper ref --force

The target is now ready to be used by sb2.

Compile the simple C program

Again run:

 sb2 gcc ~/src/hello.c -o ~/src/hello

This time:

 ~/src/hello.c:1:19: fatal error: stdio.h: No such file or directory

This is because the target has no development header files in it.

We need to be at the target root (this is bug #239) and then we can install some basic header files: Note the important use of the "-m sdk-install" and the "-R". The -m tells sb2 to use a mapping mode that permit the updating of the target and -R tells sb2 to run as fake root.

 cd /parentroot/srv/mer/targets/mer-core-armv7hl-xorg-basic-qmlviewer
 sb2 -m sdk-install -R zypper in glibc-devel

You'll need to do this for any build requirements of your code.

SB2 Detailed setup information

The sb2-init options mean:

  -d : make this the default target
  -L : linker options
  -C : compiler options
  -c : which qemu to use
  -m : which mapping to use by default
  -n : don't build libtool
  -N : don't do localisation for the target
  -t : the location of the build tools
  mer-core : The name of the target
  /opt/cross/bin/armv7hl-meego-linux-gnueabi-gcc : the cross-compiler to use

Alternate targets

N950 Nemo

To setup cross compiling for N950 (armv7hl) do the following inside the sdk chroot

Setup target

Extract the Nemo N950 rootfs as a target and set file permissions:

mkdir -p /srv/mer/targets/n950rootfs
cd /srv/mer/targets/n950rootfs
sudo tar xjvf /path/to/nemo-n950-image.tar.bz2
sudo chown -R $USER .

Initialize scratchbox2

cd /srv/mer/targets/n950rootfs
sb2-init  -L "--sysroot=/" -C "--sysroot=/" -c /usr/bin/qemu-arm-dynamic -m sdk-build -n -N -t / nemo-n950 /opt/cross/bin/armv7hl-meego-linux-gnueabi-gcc

The compiler should now work but you are still missing libraries to compile against. Install what you need into the n950 rootfs by

sb2 -m sdk-install -R zypper ref
sb2 -m sdk-install -R zypper install  ...  (eg qt-devel)

If the installation fails due to permission errors give your user write permissions to the places the packages are being installed and retry. After this you can compile for example a c hello world by

cd
cat << "EOF" > hello.c
#include <stdio.h>
int main(int argc, char **argv)
{
   printf("Hello\n");
   return 0;
}
EOF

To run a simple compile, tell sb2 what target to use (ie the name used in the sb2-init):

sb2 -t nemo-n950 gcc hello.c -o hello

Verify that the compilation worked

$ file hello
hello: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.25, not stripped
$ sb2 ./hello 
Hello

More typically you'll use

 sb2 -t nemo-n950 make

Additional Notes

Installation

If your SDK did not have the SB2 tools installed then you can do:

 sudo zypper ar http://releases.merproject.org/releases/latest/builds/i486/cross mer-cross-tools
 sudo zypper ref
 sudo zypper in sdk-sb2-config qemu-usermode mpc cross-armv6l-gcc cross-armv6l-binutils cross-armv7l-gcc cross-armv7l-binutils cross-mipsel-gcc cross-mipsel-binutils cross-armv7hl-gcc cross-armv7hl-binutils

Directory Mappings

SB2 uses a sophisticated file mapping system to access the right tools and the right source code. The definitions are stored in /usr/share/scratchbox2/modes/sdk-build/fs_rules.lua

The current SDK definitions recognises a few filesystems:

/home
/mer
/maemo
/everything

Additional entries can be made if your source lives elsewhere (eg /media or /data etc).