1.1.7. GCC ToolChain¶

Overview

The Processor SDK Linux package contains an ARM-based toolchain for Cortex A devices. The ARM toolchain also enables hardware floating point (hardfp) support. Older toolchains including arm-arago-linux-gnueabi- uses software floating point (softfp). This results in software built using a hardfp toolchain being incompatible with software built with a softfp toolchain.

ARM Toolchain

The Processor SDK Linux package uses an ARM-based tool chain. Other than using a newer version of GCC, the ARM tool chain also supports hard floating point, also known as Hard-FP. Hard-FP uses the FPU on the ARM instead of simulating it. Older tool chains including the Arago tool chain uses soft floating point (Soft-FP). Binaries built using a soft-fp tool chain are not compatible with binaries built using a hard-fp. Therefore, you must rebuild all binaries to use either hard-fp and soft-fp since you can’t mix and match. By default, all binaries included in the Processor SDK Linux package will be built for hard-fp.

The name of the toolchain binaries have also been updated from older versions of the SDK. Previous versions may have used a prefix of “arm-arago-linux-gnueabi-”. Current SDK ARMv7 toolchains use a prefix of “arm-linux-gnueabihf-” For example, the new toolchain’s gcc compiler is named arm-linux-gnueabihf-gcc.

Linux-Devkit Structure

Here is the structure of the Linux-devkit directory within the SDK.

Location in SDK

The toolchain is located in the Linux SDK in the <SDK INSTALL DIR>/linux-devkit directory. The following sections will cover the key components of the toolchain.

Cross-Compilers/Tools

The cross-compilers and tools such as qmake2 can be found the the <SDK INSTALL DIR>/linux-devkit/sysroots/x86_64-arago-linux/usr/bin directory. Adding this directory to your PATH will allow using these tools. For example:

host# export PATH="<SDK INSTALL DIR>/linux-devkit/sysroots/x86\_64-arago-linux/usr/bin:$PATH"

Additional tools are also located here such as the qmake2, rcc, uic tools used by Qt. In addition there is a qt.conf file that can be used by tools such as Qt creator to use the pre-built libraries found in the Linux SDK.

Toolchain Prefix

The cross-compile tools are prefixed with a unique target triplet which indicates the architecture and OS of the output executable code. For example, the prefix arm-linux-gnueabihf- indicates the ARMv7 achitecture running the Linux OS, and thus the corresponding GCC cross compiler is called arm-linux-gnueabihf-gcc.

Reference the table below for all toolchain prefixes and their corresponding architectures found in Processor SDK.

In an effort to be succient, the specific toolchain prefix will be replaced with ${TOOLCHAIN_PREFIX} in the examples below. In fact, the environment-setup script, described below, will set this variable in your environment.

Cross-Compiled Libraries

The toolchain within the Linux SDK contains more than just the cross-compiler, it also contains pre-built libraries that can be used in your applications without requiring you to cross-compile them yourself. These libraries include packages from alsa to zlib. The libraries are located in the <SDK INSTALL DIR>/linux-devkit/sysroots/<device specific string>-vfp-neon-linux-gnueabi/ directory. For a list of the libraries you can refer to the software manifest found in the <SDK INSTALL DIR>/docs directory or look at the list of libraries available in the <SDK INSTALL DIR>/linux-devkit/sysroots/<device specific string>-vfp-neon-linux-gnueabi/usr/lib directory. You will also find the header files corresponding to these libraries in the <SDK INSTALL DIR>/linux-devkit/sysroots/<device specific string>-vfp-neon-linux-gnueabi/usr/include directory. Usage of these libraries will be covered in more detail in the next sections, but as an example if your application wants access to the alsa asound library then you can now do the following command (assuming you have added the cross compiler to your PATH):

host# ${TOOLCHAIN_PREFIX}gcc -lasound app.c -o app.out

environment-setup script

When cross-compiling packages that use configuration tools and autotools there are many settings that are required to make sure that the proper cross-compile libraries are used. The environment-setup script located in the <SDK INSTALL DIR>/linux-devkit directory handles this for you. This script exports variables to perform actions such as:

• Adding the toolchain to the PATH
• Setting up CPATH
• Setting up PKG_CONFIG_* paths
• Setting standard variable such as CC, CPP, AR to the cross-compile values

To use the environment-setup script you only need to source it. This is as simple as:

host# source linux-devkit/environment-setup

To know if the environment setup script has been sourced in your current shell the shell prompt will be changed to contain the [linux-devkit]: prefix in the command prompt.

The Usage section below will cover some cases where using the environment-setup script is useful.

When Compiling the Linux Kernel

Because environment-setup changes standard variables such as CC you should not use this script when compiler projects that build host-side as well as target-side tools. A prime example of this is the Linux kernel, which builds some host side tools to help during the kernel build. If the environment-setup script has been sourced then the CC value will specify the cross-compiler for the host-side tool build. This means that the tools compiled and used during the kernel build will be compiled for the ARM platform while the kernel build tries to run these tools on an Intel platform. This will cause the tools to fail to run and the kernel to fail to compile.

Usage

The following sections give some examples of how to use the included toolchain to compile simple applications such as HelloWorld to more complex examples such as configuring and compiler GStreamer plugins.

Simple Cross-Compile

In the simplest case the cross-compiler can be used to compile simple applications that just need access to standard libraries. The two examples below cover an application that uses only the standard libgcc libraries and another example that uses the pthreads threading library.

HelloWorld

Simple applications like HelloWorld can be compiled using just a call to the cross-compiler since the cross-compiler can find the libraries it was built with without any issues. The following steps will show how to make a simple helloworld application and cross-compile that application.

Create a helloworld.c file

#include <stdio.h>

 int main() {
     printf ("Hello World from TI!!!\n");
     return 0;
 }

Cross-compile the helloworld.c file using the cross-compile toolchain. In this example we will invoke the toolchain without it having been added to our PATH.

host# <SDK INSTALL DIR>/linux-devkit/sysroots/x86_64-arago-linux/usr/bin/${TOOLCHAIN_PREFIX}gcc helloworld.c -o helloworld

After the above steps are run you should now have a helloworld executable in your directory that has been compiled for the ARM. A simple way to check this is to run the following command:

host# file helloworld

This should yield output like:

helloworld: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, with debug_info, not stripped

Using PThreads

In many cases your simple application probably wants to use additional libraries than the standard libgcc and glibc libraries. In this case you will need to include the header files for those libraries as well as add the library to the compile line. In this example we will look at how to build a simple threading application and use the pthread library. This example was derived from the example code at **http://www.amparo.net/ce155/thread-ex.html**

Create a file thread-ex.c with the following contents

#include <unistd.h>;
#include <sys/types.h>;
#include <errno.h>;
#include <stdio.h>;
#include <stdlib.h>;
#include <pthread.h>;
#include <string.h>;

int print_message_function(void *ptr);

/* struct to hold data to be passed to a thread
this shows how multiple data items can be passed to a thread */
typedef struct str_thdata
{
    int thread_no;
    char message[100];
} thdata;

int main(int argc, void **argv)
{
    pthread_t thread1, thread2;
    thdata data1, data2;

    data1.thread_no = 1;
    strcpy(data1.message, "Hello!");

    data2.thread_no = 2;
    strcpy(data2.message, "Hi!");

    pthread_create (&thread1, NULL, (void *) &print_message_function, (void *) &data1);
    pthread_create (&thread2, NULL, (void *) &print_message_function, (void *) &data2);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);

    exit(0);
}

int print_message_function ( void *ptr )
{
    thdata *data;
    data = (thdata *) ptr;  /* type cast to a pointer to thdata */

    /* do the work */
    printf("Thread %d says%s \n", data->thread_no, data->message);

    return 0;
}

Cross-compile the thread-ex.c file using the cross-compile toolchain. In this example we will first add the toolchain to our PATH. This only needs to be done once. We will also add the pthread library to the compile line so that we will link with the library file that provides the pthread_* functions.

host# export PATH="<SDK INSTALL DIR>/linux-devkit/sysroots/x86_64-arago-linux/usr/bin/:$PATH"

host# ${TOOLCHAIN_PREFIX}gcc -lpthread thread-ex.c -o thread-ex

Configure/Autotools

The last case to cover is one where the environment-setup script is useful. In this case we will download the gst-plugins-bad package and configure and build it using the environment-setup script to configure the system for the autotools to properly detect the libraries available as pre-built libraries.

1. First download the gst-plugins-bad-0.10.11.tar.gz package wget http://gstreamer.freedesktop.org/src/gst-plugins-bad/gst-plugins-bad-0.10.11.tar.gz

   IMPORTANT In order to build the gst-plugins-bad package you will need libglib2.0-dev installed on your system. You can install this using sudo apt-get install libglib2.0-dev

2. Extract the plugins tarball tar zxf gst-plugins-bad-0.10.11.tar.gz

3. Change directory into the extracted sources cd gst-plugins-bad-0.10.11

4. Source the <SDK INSTALL DIR>/linux-devkit/environment-setup script to prepare to configure and build the plugins. source <SDK INSTALL DIR>/linux-devkit/environment-setup

5. Now configure the package. We need to define the host setting to tell the configuration utility what our host system is, and we will also disable some plugins that are known to be bad. ./configure –host=i686 –disable-deinterlace2 –disable-x264

6. When the configuration is done the last sections will show which plugins will be build based on the libraries available. This is the key point behind what the environment-setup script provides. By setting up the PKG_CONFIG_* paths and other variables the configure script was able to check for required libraries being available to know which plugins to enable. Now that the sources have been configured you can compile them with a simple make command. make