makefile tricks

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6.3.1 Substitution References

A substitution reference substitutes the value of a variable with alterations that you specify. It has the form $(var:a=b) (or ${var:a=b}) and its meaning is to take the value of the variable var, replace every a at the end of a word with b in that value, and substitute the resulting string.

A substitution reference is actually an abbreviation for use of the patsubst expansion function

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rpath

$ORIGIN is a special variable that means ‘this executable’, and it means the actual executable filename, as readlink would see it, so symlinks are followed. In other words, $ORIGIN is special and resolves to wherever the binary is at runtime.

• GNU Linker 和 RPATH
• How to include correctly -Wl,-rpath,$ORIGIN linker argument in a Makefile?

You need to pass the literal string $ORIGIN/../lib as an argument to your linker. The $ORIGIN token is kept inside your program after it's created and when the runtime linker starts to run your program it will replace $ORIGIN with the current path that your program was invoked from.

In order to pass a literal $ to the command invoked by a make recipe, you have to escape the $ by doubling it: $$. Otherwise, make will see the $ as introducing a make variable or function. Remember, it's perfectly legal for a make variable to avoid the parentheses etc., if it's a single character (note, $@, $<, etc.)

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dependencies auto-generation

• Makefile auto dependencies with GCC
• GNU make: clean target depends on includes
• A basic, modern, idiomatic GNU makefile
• A Super-Simple Makefile for Medium-Sized C/C++ Projects

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Makefile

rules

ordinary rules

• 多个目标的时候，所有目标只能有同样的prerequisites

static pattern rules

• 其实是相当于写了很多explicit rules

• 每个target必须跟target pattern相匹配

implicit rules

其实是一些惯用的(customary)处理方法。

• 用pattern rules来定义

• 需要所有前置条件exists and can be made it is mentioned explicitly in the makefile as a target or a prerequisite, or if an implicit rule can be recursively found for how to make it.

• make会为每个没有recipe的target找implicit rule

• 只在prerequisites里提到的文件

• explicit prerequisites不影响implicit rule search

built-in rules

• make的惯例，对于.x源文件

  • 预处理PREPROCESS.x

  • 编译COMPILE.x

  • 链接LINK.x

pattern rules

• %的扩展在所有变量扩展之后

• 只有在所有prerequisites exists or can be made时才会应用

• pattern match

  • target-pattern不包含‘/’时，匹配前会先将文件路径中的目录部分去掉，只匹配文件名。对prerequisite-pattern替换完后再在前面加上目录部分。

multiple targets

对于ordinary rules

• 相当于很多具有相同prerequisites和recipe的rules

对于implicit rules

• 一个recipe生成所有targets

自动依赖生成

编译器参数

• -MMD根据-o值放.d文件

• -MP对每个prerequisite加一个phony target，这样，文件被删的时候就不会报错了

directory organization

rules的选择顺序

1. ordinary rules

2. static pattern rules

3. implicit rules即pattern rules

• 3.1 stem短的优先

• 3.2 先定义的优先

4. chain rules

expansion

target和prerequisite立刻展开

运行机理

1st phase: 建依赖图

2nd phase: 决定哪些需要rebuild