通用Makefile中必需的预构建规则

Question

I'm compiling C++ code for Webots (a robotic simulator), by means of makefiles, and I'm using the generic makefile Makefile.include Webots supplies to ease the process.

I build by own makefile, set a bunch of required variables and then call that makefile that sets all the necessary rules for compilation. That's how it was supposed to work anyway.

I'm getting the following error:

make[1]: *** No rule to make target 'USER_PREBUILD'.  Stop.
/usr/share/webots/resources/Makefile.include:503: recipe for target 'pre-build' failed
make: *** [pre-build] Error 2

And looking at the relevant line (from Makefile.include ):

$(SUPPORTED_TARGETS): post-build

USER_PREBUILD:

USER_POSTBUILD:

pre-build:
    @$(MAKE) --silent USER_PREBUILD

post-build: main-build
    @$(MAKE) --silent USER_POSTBUILD

$(TARGETS): pre-build

main-build: $(TARGETS)

I'm not sure if there is not a syntax error when calling make in the pre-build and post-build , or if USER_PREBUILD and USER_POSTBUILD are supposed to be concrete files, but even if replace them with $(USER_PREBUILD) I get *** No targets specified and no makefile found . So I assume I would need to set those variables before calling the external makefile, but what exactly is the syntax if I don't have anything to be done before building?

Strangely, even despite these errors, the program compiles (I get the *.o, *.d and the binary on the build folder), but it never copies the binary to the destination folder.

Answer 1

That's a bit of an odd way to have set things up in that file.

The USER_PREBUILD: and USER_POSTBUILD: lines have no effect and are not doing anything for anyone (at least that I'm aware of).

You have two choices for how to solve this problem.

You can provide empty rules for the USER_PREBUILD and USER_POSTBUILD targets in your makefile:

USER_PREBUILD USER_POSTBUILD: ;

or you can avoid even the attempt at running those targets (at the cost of an over-riding warning message from make) by using these lines:

pre-build: ;
post-build: main-build ;

in your makefile after the inclusion of Makefile.include .