Re: problems depending on -l

[Karen Paffendorf]

Hi Mike,

Thanks - getting closer.

Adding -Wl,-soname=$(@F) when building that target in a directory 
generated the ldd results that seem to work at runtime.
(Still need a resolution of the problem that I reported to the bug team: 
The library only builds if the directory exists.
It does not trigger the rule that builds the directory the library get 
built in. See below for code to reproduce what I perceive as a bug.)

Unfortunately modifying the vpath did not change which libm got chosen, 
so the error continued as before.
Should I report this as a bug?

Karen

# Simple make file to reproduce "knowing how to make library" failure

#$ gmake -f pre.mk whatever
#gmake: *** No rule to to make target `-lmy', needed by `whatever'.  Stop.
#$ mkdir exists
#$ gmake -f pre.mk whatever DIR=exists
#touch exists/libmy.so
#exists/libmy.so
#$



DIR=not_exists

$(DIR):
        mkdir -p $(DIR)

$(DIR)/libmy.so:
        touch $@

whatever: -lmy
        @echo $^

vpath libmy% $(DIR)


Mike Shal wrote:

> On 12/1/05, Karen Paffendorf <address@hidden> wrote:
>  
>
> > Hi,
> >
> > I seem to be having two different problems with putting -l... as a
> > dependency and linking $^ with gcc.
> >
> > In the first, I am building my own library in a subdirectory
> > (using a "vpath libmy% my_directory" and "executable: -lmy"
> > and having runtime problems because the library exists in a different place.
> >
> > ldd yields
> >  my_directory/libmy.so => not found
> >
> > if I gcc with the -lmy instead of the generated my_directory/libmy.so
> > the problem goes away.
> >
> > ldd yields
> >  libmy.so => ???/libmy.so
> > and the executable runs.
> >
> > Am I missing something in the compiler or ldd conf?
> >    
>
> I believe in this case you can build the library using the -soname
> flag to the linker. I think you'd want to pass in '-soname libmy.so'.
> This tells the linker to use the 'libmy.so' name instead of the name
> you pass on the command line (the 'my_directory/libmy.so' as you have
> above). You shouldn't have to change the command line that then links
> in libmy.so, only the command to build libmy.so.
>
>  
>
> > in the second on RH4 x86_64, -lm failed by explicately pulling in
> > /usr/lib/libm.so, which was the wrong format.
> > If the command included -lm, ldd showed it pointing to /lib64/libm.so.6
> > It worked fine in my other build environments.
> >    
>
> Not sure on this, I'm guessing it's because make's search algorithm
> differs from your compiler's. According to the make manual, make will
> search:
>
>  directories specified by matching `vpath' search paths
>  and the `VPATH' search path, and then in the directories `/lib',
>  `/usr/lib', and `PREFIX/lib' (normally `/usr/local/lib'...
>
> So maybe you just need to add /lib64 to VPATH so make knows about it?
>
> Hope this helps,
> -Mike
>