Linux Development Process

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Linux Build Process Components :

Terminology :

  • Build System is the machine Which is building  Tool chain components.
  • Host System is the machine Where software development using tool chain being done.
  • Target System is the machine where generated code to be executed.
  • If all above are being done in a single machine, It is called native based development. For ex: x86
  • If Build and Host systems are different but final Target is Host m/c itself ,It is called cross-native.
  • If all above are being done in two or more machines, It is called cross tool chain based development. For ex code was generated in x86 but executed in PowerPC/ARM/MIPS/RISCV

If all above are being done in three different machines, It is called Canadian system. For ex: Tool chain was build in a fast x86 based m/c. The build tool chain binary was used in another x86 based m/c to generate code for the target x86 based system .

Tool chain Components :

Have you heard about Recursive Acronym ?  If not , Look for same at the end of this blog.

The basic components of any tool chain are compiler, assembler and linker. Compiler parses the C language tokens to assembly, Assembly converts that to binary objects and finally Linker combines all these objects with pre-built libraries to generate the final executable file. GNU tool chain components are as follows :

GNU Compiler Collection(GCC) : A set of compilers for several programming languages

GNU Debugger (GDB) : Used for source level debugging of application at run time

GNU Binutils : A set of tools including Assembler, Linker , Strip utility and other tools to build target executable file.

GNU C Lbrary(glibc) : It is the implementation of standard C library and some other useful stuff related to kernel interface. i.e. printf(),malloc, system calls etc.

  1. Static libraries: The static library object code is linked with the application. It is basically archive(.a)  of objects.

     

  2. Shared libraries  or Dynamically linked libraries(DLL) are libraries that are loaded by programs when they start. When a shared library is installed properly, all programs that start afterwards  automatically use the new shared library.
  3. Dynamically linked shared object libraries (.so): It can be used in following ways. This gives flexibility to change a particular library version while program is running.
    1. Dynamically linked at run time. The libraries must be available during compile/link phase. The application binary doesn’t include these shared objects but is aware of these..

    2. Dynamically loaded/unloaded and linked during execution using the dynamic linking loader system functions.

 

     gcc src-file.c -lm

Here Linker will use the math library. Math library is in /usr/lib/libm.a

Library naming conventions:

Every shared library has a special name called the “soname”. This follows a format .so.[major ABI version].[minor version1].[minor version2…]

sanjay@sanjay-VirtualBox:~/linux_day6$ ./hello &

dev1

Why there is a difference in name of library file shown by ldd and lsof ? 

 

Every shared library also has a “real name”, which is the filename containing the actual library code. The real name adds to the soname .[minor number].[release number]. Linker will use only soname. You may use ldd (List Dynamic Dependencies) to find required shared libraries by an application.

 

References

 

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