Question

according to the manual you can use such syntax: libfoo(obj1.o) , which stands for insert obj1.o to libfoo, i wrote a rule like this:

libfoo(obj1.o obj2.o):obj1 obj2  

this rule only insert obj1.o to libfoo, why it just can not insert obj2.o into libfoo?
what does libfoo(obj1.o obj2.o) really stands for?

Answer 1

From the GNUMake manual:

To specify several members in the same archive, you can write all the
member names together between the parentheses. For example:

 foolib(hack.o kludge.o)

is equivalent to:

 foolib(hack.o) foolib(kludge.o)

When you make, I’m guessing you don’t specify the target, so Make chooses the first target, which in your makefile is libfoo(obj1.o).