Consider the following makefile:
all : a.vo a.glob
a.gl%b a.v% : a.v
touch a.glob a.vo
When I run make -j2, I get:
$ rm -f a.vo a.glob; make -j2
make: Circular a.v.o <- a.v dependency dropped.
touch a.glob a.vo
I see why a.v.o depends on a.v, but I don't see how a.v depends on a.v.o. Where does this dependency come from (and is there a way to disable it)?
GNU make uses Implicit Rules when no rule is defined. In particular,
n is made automatically from n.o by running the linker (usually called ld) via the C compiler. The precise recipe used is ‘$(CC) $(LDFLAGS) n.o $(LOADLIBES) $(LDLIBS)’.
As you can see:
~ $ cat Makefile
all: a.v
echo "foo"
a.v.o:
echo "bar"
~ $ make
echo "bar"
bar
cc a.v.o -o a.v
gcc: error: a.v.o: No such file or directory
gcc: fatal error: no input files
compilation terminated.
<builtin>: recipe for target 'a.v' failed
make: *** [a.v] Error 1
cc is executed.
