GNU ‘make’ Target Specific Variables are Dumb

Let’s say we have a Makefile using some target-specific variables:

$ cat Makefile 
foo = global
b : foo = for-b

all : d
        @cat d

a :
        @echo a:$(foo) > a

b : a
        @{ cat a ; echo b:$(foo) ; } > b

c : a
        @{ cat a ; echo c:$(foo) ; } > c

d : b c
        @cat b c > d

Then we can get different results depending upon how we make the ‘all’ target:

$ rm a b c d ; make 
a:for-b
b:for-b
a:for-b
c:global
$ rm a b c d ; make a b c d all
a:global
b:for-b
a:global
c:global

This is considered a feature:

There is one more special feature of target-specific variables: when you define a target-specific variable that variable value is also in effect for all prerequisites of this target, and all their prerequisites, etc. (unless those prerequisites override that variable with their own target-specific variable value).

In practice, it’s a pain in the ass. Using Quagmire, you’re supposed to be able to do this:

noinst_SHARED_LIBRARIES = libone.so libtwo.so libthree.so
    
libone.so_SOURCES = one.c
libone.so : LDFLAGS = -Wl,-soname,libone.so
libone.so_LIBS = libthree.so
    
libtwo.so_SOURCES = two.c
libtwo.so : LDFLAGS = -Wl,-soname,libtwo.so
libtwo.so_LIBS = libthree.so
    
libthree.so_SOURCES = three.c

Which leads to some rather bizarre behaviour:

$ make clean all &>/dev/null ; scanelf -S libthree.so
 TYPE   SONAME FILE 
ET_DYN libone.so libthree.so 

$ make clean libone.so &>/dev/null ; scanelf -S libthree.so
 TYPE   SONAME FILE 
ET_DYN libone.so libthree.so 

$ make clean libtwo.so &>/dev/null ; scanelf -S libthree.so
 TYPE   SONAME FILE 
ET_DYN libtwo.so libthree.so 

$ make clean libthree.so &>/dev/null ; scanelf -S libthree.so
 TYPE   SONAME FILE 
ET_DYN  libthree.so 

I can think of a few not very nice ways of getting around this. Hopefully someone will come up with something better…