building libtorrent for C.H.I.P.™

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I recently bought a C.H.I.P. and naturally wanted to build libtorrent for it. I’m on a mac and chip runs arm, so first I needed to install the cross compiler toolchain. The target for chip is arm on linux, so the toolchain I’m looking for is “arm-linux-gnueabihf”.

toolchain

It seems like a fair number of people online suggest using “gcc-arm-none-eabi”, presumably because that’s a package that’s easily available on homebrew. However, having a generic build, not for linux, means linux specifics won’t work. Specifically, the “-pthread” argument is not recognized by that variant of GCC.

There are old binaries for a linaro gcc cross compiler build for mac OS here. This installs all the gcc and binutils we need:

arm-linux-gnueabihf-g++
arm-linux-gnueabihf-ar
arm-linux-gnueabihf-ld
... etc ...

The tools we’re especially concerned with are arm-linux-gnueabihf-g++ (the compiler) and arm-linux-gnueabihf-ar (the archiver for making static libraries) and arm-linux-gnueabihf-ld (the linker). Let’s first check out the compiler:

$ arm-linux-gnueabihf-g++ --version
arm-linux-gnueabihf-g++ (crosstool-NG linaro-1.13.1-4.9-2014.05 - Linaro GCC 4.9-2014.05) 4.9.1 20140505 (prerelease)
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

user-config.jam

Next we need to configure boost build to know about this version of gcc. It’s possible to configure toolsets per project, but I like to configure my toolsets user-wide. For this, you put the definition in ~/user-config.jam.

The rule for configuring a toolset in boost build is “using” and its synopsis is:

using toolset : version : compile-command : options ;

toolset: The toolset is called gcc.
version: To avoid clashing with the system compiler, we give this configuration of the toolset a unique name, “chip”. It will be referred to as “gcc-chip” on the b2 command line later.
compile-command: This is the command to run the compiler, “arm-linux-gnueabihf-g++”.
options: You need to specify which target-os and architecture this toolset builds for, you do this with:

<target-os>linux <architecture>arm

In this case I have an older version of GCC that doesn’t default to C++11, so I also need to specify:

<cxxflags>-std=c++11 <linkflags>-std=c++11

boost build will link via the compile command, but it will need to know which archiver to use to build static libraries/archives. You specify that like this:

<archiver>arm-linux-gnueabihf-ar

Putting it all together you get this line in your ~/user-config.jam:

using gcc : chip : arm-linux-gnueabihf-g++ : <archiver>arm-linux-gnueabihf-ar
   <cxxflags>-std=c++11 <linkflags>-std=c++11 ;

Keep in mind that whitespace matters in jam. You need those spaces around “:” and “;”.

This configures a GCC compiler for the specified target operating system and architecture.

building libtorrent

To build libtorrent for this target, in the libtorrent example directory, run:

$ b2 gcc-chip -j4 link=static target-os=linux architecture=arm release

For a development build, you want to disable invariant checks, since they can be quite expensive, causing poor run-time performance:

$ b2 gcc-chip -j4 link=static target-os=linux architecture=arm invariant-checks=off

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