Let’s install Gentoo on our Raspberrypi, it’s just a proof of concept since binary compilation takes too long on this hardware. In future articles, we will explain how to compile using distcc and cross-dev ;)

We generate the necessary partitions:

Disposit. Inicio Comienzo Fin Bloques Id Sistema
/dev/mmcblk0p1 * 2048 1050623 524288 c W95 FAT32 (LBA)
/dev/mmcblk0p2 1050624 2099199 524288 82 Linux swap / Solaris
/dev/mmcblk0p3 2099200 61497343 29699072 83 Linux

NOTE: The minimum size of a FAT32 partition is 512Mb.

We create the boot, swap, and root file systems:

We mount the partitions:

We download the stage:

We download the portage:

We download the Rasp firmware files:

We chroot:

Now we must chroot to our Rasp root dir, but it is not possible to chroot from a different architecture, AMD64 –> ARM.

Therefore, we will make a workaround using qemu, which will execute the commands inside the chroot emulating the ARM architecture.

For this to work, we must have the following enabled in the kernel:

Executable file formats / Emulations ---> [*] Kernel support for MISC binaries

Once the chroot is done, the OS no longer knows anything about the previous system. In reality, a binary from the outside is being executed, in this case qemu inside a chroot with ARM architecture. When executing the commands, q-emu will look for AMD64 q-emu libraries in the chroot (ARM). To avoid this, we will compile q-emu statically. Compiling qemu statically in Gentoo can be complicated, so we will download the Debian version and extract the statically compiled qemu binary using alien:
http://http.us.debian.org/debian/pool/main/q/qemu/

We extract the deb:

We will configure our OS so that when it detects that a binary compiled for the ARM architecture is being executed, it does so through qemu. We will execute a wrapper that in turn will execute /opt/qemu-arm-rpi/qemu-arm.

The steps that will be executed are:

chroot /bin/bash -- This bash is ARM --> /opt/qemu-arm-rpi/qemu-wrapper --> /opt/qemu-arm-rpi/qemu-arm

We copy the ARM interpreter:

We compile the wrapper:

#include <string.h>
#include <unistd.h>

int main(int argc, char **argv, char **envp) {
char *newargv[argc + 3];
newargv[0] = argv[0];
newargv[1] = "-cpu";
newargv[2] = "arm1176";
memcpy(&newargv[3], &argv[1], sizeof(*argv) * (argc - 1));
newargv[argc + 2] = NULL;
return execve("/opt/qemu-arm-rpi/qemu-arm", newargv, envp);
}

We configure the OS to execute the wrapper in case it is ARM:

If you have Kernel support for MISC binaries as a module:

Prepare the chroot environment:

Enter:

NOTE: If we experience memory problems, we must define the variable: QEMU_RESERVED_VA

Configure Gentoo normally:

default/linux/arm/13.0/armv6j

USE="-X -gnome -kde -ipv6 -mono -doc -java -fortran -openmp"

Define the boot config parameters:

dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p3 rootfstype=ext4 elevator=deadline rootwait

Continue with the system config:

/dev/mmcblk0p1 /boot vfat auto,noatime 1 2
/dev/mmcblk0p3 / ext4 noatime 0 1
/dev/mmcblk0p2 none swap sw 0 0

config_eth0=( "dhcp" )

es_ES.utf8 UTF-8
es_ES@euro ISO-8859-15

LANG="es_ES.utf8"
LC_COLLATE="C"

# SERIAL CONSOLES
#s0:12345:respawn:/sbin/agetty 9600 ttyS0 vt100
#s1:12345:respawn:/sbin/agetty 9600 ttyS1 vt100

NOTE: If the gcc version is updated

With this, we will have the SD card ready to plug into the Rasp and work. In future articles, we will explain how to compile using distcc and cross-dev ;)