Book Image

Mastering Embedded Linux Programming

By : Chris Simmonds
Book Image

Mastering Embedded Linux Programming

By: Chris Simmonds

Overview of this book

Mastering Embedded Linux Programming takes you through the product cycle and gives you an in-depth description of the components and options that are available at each stage. You will begin by learning about toolchains, bootloaders, the Linux kernel, and how to configure a root filesystem to create a basic working device. You will then learn how to use the two most commonly used build systems, Buildroot and Yocto, to speed up and simplify the development process. Building on this solid base, the next section considers how to make best use of raw NAND/NOR flash memory and managed flash eMMC chips, including mechanisms for increasing the lifetime of the devices and to perform reliable in-field updates. Next, you need to consider what techniques are best suited to writing applications for your device. We will then see how functions are split between processes and the usage of POSIX threads, which have a big impact on the responsiveness and performance of the final device The closing sections look at the techniques available to developers for profiling and tracing applications and kernel code using perf and ftrace.
Table of Contents (22 chapters)
Mastering Embedded Linux Programming
About the Author
About the Reviewers

Looking at the components of the C library

The C library is not a single library file. It is composed of four main parts that together implement the POSIX functions API:

  • libc: The main C library that contains the well-known POSIX functions such as printf, open, close, read, write, and so on

  • libm: Maths functions such as cos, exp, and log

  • libpthread: All the POSIX thread functions with names beginning with pthread_

  • librt: The real-time extensions to POSIX, including shared memory and asynchronous I/O

The first one, libc, is always linked in but the others have to be explicitly linked with the -l option. The parameter to -l is the library name with lib stripped off. So, for example, a program that calculates a sine function by calling sin() would be linked with libm using -lm:

arm-cortex_a8-linux-gnueabihf-gcc myprog.c -o myprog -lm

You can verify which libraries have been linked in this or any other program by using the readelf command:

$ arm-cortex_a8-linux-gnueabihf-readelf -a myprog | grep...