Conditionals and including other makefilesĬonditionals are used throughout the common.mk makefile. This operator is mostly used to append all arguments for GCC to single variable. To append values to variables, the += operator is used. Refer to the makefile options cheatsheet to see which variabels can be set in a project makefile. STM32-base uses this way of setting variables to allow the used to overwrite the value of these variables in their projects makefile. This allows for setting these variables in another makefile. Variables set with the ?= operator are set, only if that variable has not yet been set at that point. This operator just sets the variable to the given value. Some variables are set with the = operator. Most variables used in this makefile are also set in this makefile. Most lines in the common.mk makefile have something to do with variables. It will, however, highlight some of the important parts of these makefiles and link to related documentation if appropriate. This article will not explain how the STM32-base makefiles work line-by-line.
The common.mk makefile located in the make directory in the STM32-base repository contains all these so-called rules. For more general information on make, visit the GNU make website. To learn how make works, refer to the official GNU make manual. This enables make to only update those files that have been changed. In addition to being less error prone, make is also able to detect changes made to (source) files. However, due to the large amount of arguments that need to be passed to GNU GCC, it is less error prone to automate this process.
The programs make runs are not different from those one could run by hand in a terminal window. These rules are defined in the makefiles. The programs that make will run are defined by so-called rules. Makefiles are processed by a program called make. STM32-base uses makefiles to automate the process of compiling C and C++ code.
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