Kconfig Kbuild

In code engineering, we often see some projects called Kconfig Kbuild The file of
The purpose of this document is ： Compile oriented script , Shield hardware differences .Kconfig It's not a special script , It's a way to solve the problem , He can do it in any way ：python、shell+makfefile（linux kernal、Busybox）.

1. Introduction

   For embedded or OS for , Faced with hundreds of hardware types , for instance .
   If there are two I2C The hardware needs to be adapted , Common practice ：

   • Method 1 （ It is not recommended to abuse this method ,1 The same file will be modified when adding a board , Risk of incorrect modification 2 Not conducive to reading ）

     One .c Distinguish by macro Then compile the script / Compile macros to distinguish
     #ifdef I2C_A_HARDWARE
     void i2c_write()
     #endif

     #ifdef I2C_B_HARDWARE
     void i2c_write()
     #endif

   • Method 2

     Distinguish by file i2c_ahardware.c i2cb_hardware.c Finally, it is also distinguished by compiling scripts

     For the second method , When adding a hardware , The built script needs to be modified ：

     if I2C_A_ chip
     i2c_ahardware.c Participate in building
     else if I2C_B_ chip
     i2cbhardware.c Participate in building
     else if I2C_X_ chip
     i2cx_hardware.c Participate in building
     …
     else if chip xxx
     …
     …
     …
     endif

   You can imagine when there are hundreds of chips ,makefile What will it be like , Let alone if else Nested scenes 、 File path modification 、 File name modification 、 Code integration , The modification of the compiled script caused by , really ....

   Think about it
   linux kernal How a set of code fits thousands of boards
   U-boot How to support thousands of boards

2. Kconfig How it works

   Kconfig Working steps of
   1） Read... In the current directory .config file （ If not, follow Kconfig File default configuration ）
   2） according to .config The content of , Display the corresponding interface
   3） The programmer selects the components of the board to be built through the interface
   4） sign out Kconfig Interface , Two files will be saved ：.config、autoconf.h

   Kconfig file ：
   
   Kconfig Interface after file operation ： Users choose （* For choice ）
   
   Generated .config file （ This file can be used to initialize Kconfig Interface , It can also be saved as configuration files of different hardware . Use different configuration files to replace complex if else）
   

   Kbuild file ： Include and exclude the selected files
   
   When choosing I2C_A, The final obj-y = i2c_a_hardware.o This is the input of the compilation script .

   autoconf.h （ according to Kconfig The selection result of , It can be used as a method 1 Macro definition file ）
   
   Kconfig Of python Implementation code can refer to ：
   github project ulfalizer/Kconfiglib
   The use of this library ：
   https://blog.csdn.net/u010018991/article/details/81867316

3. summary

   • Kconfig It is equivalent to layering the functions of the compiled script , Shielding all kinds of boards 、 Chip differences
   • The original if else Branch still " There is ", It is only branched by multiple hardware boards .config Profile substitution
   • Kconfig It can also be applied to pure software scenarios , It can support cutting and customization of pure software

   There are two ways to use in your own project Kconfig
   Linux Kernel Used a bunch of scripts , stay scripts Under the table of contents , Belong to GPL agreement .
   Kconfiglib Is another option , It USES Python Script to achieve Kconfig, This library License More friendly to business software .