No rule to make target ... libm.a

Question

I get the following error when I try to compile my app:

*** No rule to make target `/mypath/lib/libm.a', needed by `/myPath/bin/appName'

Why is the linker looking for libm.a according to an absolute path?

Answer 1

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Why is the linker looking for libm.a according to an absolute path?

Because you told him to do so. Most likely you've typed

# There were some rules that build your own .a libs
myLib.a: ...
   ...

# Handy rule to direct your libs into lib/ folder!
vpath %.a /mypath/lib

appName: appName.o libm.a
   g++ $^ -o $@

Whoops! You need "system" libm.a (that's a math library, a part of glibc), but make thinks that you need your own static library. It then adds the proper prefix and doesn't find any rule to remake libm.a.

A solution could be moving libm.a out of prerequisites. That's the purpose of configure script or a special make sanity target to check the existence of system libraries.

EXT_LIBS=libm.a

appName: appName.o
   g++ $^ $(EXT_LIBS) -o $@