为什么.PHONY在这种情况下不起作用? [英] Why does .PHONY not work in this situation?

问题描述

我有一个复杂的makefile，似乎每次调用它都会重新链接我的库和可执行文件.我能够将问题缩小为一个简单的makefile:

I have a complicated makefile that seems to relink my libraries and executables every time I invoke it. I was able to narrow down the problem into a simple makefile:

 1: all: prog
 2:
 3: .PHONY: prog
 4: prog: prog.exe
 5:
 6: prog.exe: lib prog.o
 7:         touch prog.exe
 8:
 9: prog.o: prog.c
10:         touch prog.o
11:
12: .PHONY: lib
13: lib: lib.so
14:
15: lib.so: lib.o
16:         touch lib.so
17:
18: lib.o: lib.c
19:         touch lib.o
20:
21: .PHONY: clean
22: clean:
23:         rm *.so *.o *.exe

由于某些原因，此示例每次都会创建prog.exe.如果我将第6行的lib替换为lib.so，那么它将起作用.但是看来我应该能够做我在这里尝试的事情.我缺少什么基本的东西吗?

For some reason, this example, prog.exe is created every time. If I replace the lib on line 6 with lib.so then it works. Yet it seems like I should be able to do what I'm attempting here. Is there something fundamental I'm missing?

推荐答案

从在线GNU制作手册中:

From the online GNU make manual:

假冒目标不应是 实际目标文件的前提条件；如果 是的，它的配方每次都会运行 时间使去更新该文件.作为 只要一个虚假的目标永远不会 真正目标的先决条件 虚假目标配方将被执行 仅当虚假目标为 指定的目标(请参阅 指定目标).

A phony target should not be a prerequisite of a real target file; if it is, its recipe will be run every time make goes to update that file. As long as a phony target is never a prerequisite of a real target, the phony target recipe will be executed only when the phony target is a specified goal (see Arguments to Specify the Goals).

至少可以解释您所看到的内容.由于prog.exe依赖于lib(您用于收集库的伪造目标)，因此会触发lib规则，因此prog.exe为过时"并重新链接.

That at least explains what you are seeing. Since prog.exe depends on lib, your phony target for collecting libraries, the lib rule is fired, and hence prog.exe is "out of date", and gets relinked.

看来您必须更加明确地了解您的依赖项.也许您有兴趣将它们放在一个变量中，以使管理多个库变得更加容易?例如:

It looks like you'll have to be more explicit about your dependencies. Perhaps you would be interested in putting them in a variable to make managing multiple libraries a bit easier? For example:

LIBS = lib.so

all: libs progs

.PHONY: progs libs clean

progs: prog.exe

prog.exe: $(LIBS) prog.o
    touch prog.exe

# etc.
libs: $(LIBS)

lib.so: lib.o
    touch lib.so

# and so on

在上面的示例中，我还将伪造目标的名称更改为progs和libs，根据我的经验，这更常见.在这种情况下，libs目标只是构建所有库的便利，而不是充当实际的依赖项.

In the above example, I've also changed the names of the phony targets to progs and libs, which in my experience are more common. In this case, the libs target is just a convenience for building all the libraries, rather than acting as an actual dependency.

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