Re: Avoid relinking when .so file changes

[Henrik Carlqvist]

variablecloudiness@gmail.com wrote:
> I have a Makefile (GNU Make 3.80).  Let's say I have a target
> for a binary called 'myBinary'.  myBinary depends on a few .so
> files.  When I type 'make myBinary', and the files that generate
> those .so files change, I want the .so files regenerated.
> 
> I don't, however, want 'myBinary' relinked, since the interface to
> the .so file hasn't changed--relinking is unnecessary.

But you want the .so file created if it doesn't already exist I suppose?
 
> So far, my Makefile looks like this:
> 
> myBinary: myBinary.o myLibrary.so
>         g++ --go-go-gadget-linker

One way to fix this would be:

myBinary: myBinary.o $(filter-out $(wildcard myLibrary.so), myLibrary.so)
        g++ --go-go-gadget-linker

With the above rule myBinary depends on myLibrary.so if it doesn't
already exist. But if the file already exist it doesn't care if it is
newer than myBinary. I usually use this method for dependencies on
directories, something like this:

$(O_DIR)/%.o: $(C_DIR)/%.c $(filter-out $(wildcard $(O_DIR)), $(O_DIR))

$(O_DIR):
        mkdir -f $@

Above I want a directory created before I can put files in that directory.
However, once the directory is created I don't want to rebuild files in
it only because it has gotten a new time stamp. Every time a file is
created or deleted in a directory the time stamp of the directory gets
updated.

> How do I change this Makefile to keep the relinking from happening?
> Dropping the .so dependency creates pain, because then 'make -j' doesn't
> work right.

What is the problem with make -j? To me it seems as if dropping the
dependency only would cause the .so file not to be created, regardless of
if the -j flag is used.

regards Henrik
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