Add support for Raspberry Pi

[gavv]

• cross compilation
• warnings
• running
• ci
• instructions

[gavv]

Building toolchains in Gentoo

[gavv]

Toolchain tuples

• Debian: Multiarch Tuples
• Gentoo: Toolchain Tuples
• Linux/POSIX: Uname
• Autoconf: Specifying Target Triplets

Detecting host toolchain

Uname doesn't provide enough information. E.g., it doesn't distinguish between hardfloat and softfloat.

Autoconf uses config.guess script to detect host toolchain tuple. It prints toolchain tuple in the same form as in Gentoo. However, it differs from Debian naming. E.g. on Orange Pi, it prints armv7l-unknown-linux-gnueabihf, while Debian uses arm-linux-gnueabihf.

Another option is to invoke gcc -print-multiarch. It usually works on Debian (if multilib is enabled, it prints arm-linux-gnueabihf) but always prints empty string on Gentoo.

One another option:

$ gcc -v -E - </dev/null |& grep Target:
Target: arm-linux-gnueabihf

This works on Gentoo as well.

Detecting cross-compilation mode

• Autoconf: Hosts and Cross-Compilation

[gavv]

@baranovmv

Could you try this instructions to cross-compile Roc for your RPi A?

Both "Manually" and "Docker" sub-sections of "Raspberry Pi 1" section.

It's also interesting does debian-way approach ("Ubuntu and Debian armhf" section) work for you?

(Doesn't work for my OPi, because crossbuild-essential-armhf builds binaries that require newer Glibc than on my box.)

[gavv]

Emulating ARM in QEMU

[gavv]

I've created new task #68 for playback problems. Thus, we can close this task when our cross-compiling will work for RPi A.

[gavv]

Everything works on Orange Pi.

[baranovmv]

Any crossbuild technique for Raspberry Pi A works well.