Re: autoconf linking with shared object

[Ralf Wildenhues]

Hi Braden,

* Braden McDaniel wrote on Wed, Mar 29, 2006 at 06:18:02PM CEST:
> On Wed, 2006-03-29 at 10:41 +0200, Ralf Wildenhues wrote:
> > * Braden McDaniel wrote on Wed, Mar 29, 2006 at 10:32:37AM CEST:
> > > 
[ -l* in *_LDFLAGS ]

> > That's very likely because you rarely do static linking.
> 
> While as a matter of convenience during development I build dynamic
> libraries much more often than static ones, I do ensure my package works
> in the static case. I do use libtool, so perhaps it is insulating me
> from problems.

Nope, libtool leaves you out in the cold there.  But it's really
Automake that dictates the order of the Makefile macros in the link
command line.

> You seem to be saying "make sure all your -l flags are in the right
> order", which is a concept (I think) I understand. But I believe I've
> been doing that while putting the -l flags in *_LDFLAGS just fine.

So you have the order inside your library flags under control.  That is
one important part for static linking.

> Are you saying that use of *_LDFLAGS is somehow fundamentally
> incompatible with this goal?

Well, Automake generates something similar to this (abridged):

LINK = $(CCLD) $(AM_CFLAGS) $(CFLAGS) $(AM_LDFLAGS) $(LDFLAGS) -o $@
[...]
prog$(EXEEXT): $(prog_OBJECTS) $(prog_DEPENDENCIES)
        @rm -f prog$(EXEEXT)
        $(LINK) $(prog_OBJECTS) $(prog_LDADD) $(LIBS)

Now look at this example:

cat >m.c <<\EOF
#include <stdio.h>
#include <math.h>
int main()
{
  double x = 0.;
  printf("%g\n", sin(x));
  return 0;
}
EOF
gcc -c m.c
gcc -static -lm -o m m.o
| m.o(.text+0x1f): In function `main':
| : undefined reference to `sin'
| collect2: ld returned 1 exit status
gcc -static -o m m.o -lm; echo $?
| 0

So it's a good idea to put the library flags after all the objects.
(BTW, the variable keeps gcc from optimizing the sin call away.)

Cheers,
Ralf