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cross-compilation.md

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Cross-compiling Binaries for Vector

To cross compile binaries for Vector, we need a compiler that can produce arm binaries and matches Vector's libc version and expected application binary interface (abi).

Vector uses the Qualcomm APQ8009, which is a 32bit ARMv7l rev 5 processor.

A suitable cross compiler is available from Linaro, version 6.3.1 produces binaries that are compatible with Vector.

If you will be using an installation of Linux, either natively or in a virtual machine download the x86_64 (recommended) or i686 release.

If you will be using a Windows machine, download the i686-mingw release. This toolchain is tested and works on Windows, though the commands below will need tweaking unless run under WSL.

Build Environment

The instructions below assume an Ubuntu Linux installation. The same steps should work for any Linux distribution, minor modifications will be needed for Windows.

  1. Extract the cross-compiler somewhere convenient:

    tar xJf arm-linux-gnueabi/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi.tar.xz

Building for Vector

  1. Augment your path to include the bin/ directory for the cross-compiler:

    export PATH="${PATH}:/path/to/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi/bin"

    This can be done each time you want to compile for Vector or added to your environment files.

  2. Create a simple hello world program:

    cat > hello.c << _DONE_
#include <stdio.h>

void main() {
    printf("hello, vector!\r\n");
}
_DONE_

  3. Compile hello world for Vector:

    arm-linux-gnueabi-gcc -o hello hello.c

  4. Check the resulting build's architecture details with file hello. The expected output from this command should match:

    hello: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 2.6.32, BuildID[sha1]=<...>, with debug_info, not stripped

Running on Vector

It's important to note that Vector's filesystems have a bit of extra protection on them. Partitions which were not expected to contain executable code are mounted with the noexec option set. This will result in binaries failing to execute with Permission denied on such partitions.

To remount a partition, such as /data, as executable for testing you can run:

mount -o remount,exec /data

Note that this will only affect Vector until a reboot. If you will be writing programs you wish to be able to always run, you'll want to place your programs in the root partition somewhere or modify /etc/initscripts/mount-data to mount /data without the noexec option.

  1. Copying the binary over to Vector:

    scp -i ~/.ssh/id_rsa_Vector-AAAA hello root@1.2.3.4:/data/

    Replacing AAAA and 1.2.3.4 with your Vector's identifier and ip address.

  2. ssh into your Vector and remount /data as executable:

    mount -o remount,exec /data

  3. Run the application!

    # /data/hello
hello, vector!