Axel.Thimm@xxxxxxxxxx (Axel Thimm) writes:
> | Here's a crazy-but-not-too-far-from-reality example: Build shared-lib
> | pkg 'b' which links against 'a'. b's .la files now include references
> | to 'liba.la' (so now depends on it). Build shared-lib pkg 'c' which
> | links against 'b', whose own libc.la file includes
> | references(+dependancy) on libb.la. Rinse, lather, repeat. You'll end
> | up with a pkg z, and a libz.la, which, when all is said and done,
> |
> | * will have a direct dependancy upon y's liby.la
> | * and because of liby.la file references/dependances, will have
> | (indirect) dependancies upon liba.la, libb.la, ..., libx.la
> |
> | When, generally, *none* of these are really required nor desired.
>
> I'm not sure about that, but maybe I understand something wrongly:
>
> - If -la was needed for building libb, then there exists a real
> dependency between liba and libb and libb.la is correct about that.
No, this dependency does not need to be handled explicitly with dynamic
libraries.
E.g. a dep-tree of
liba.so -> libb.so -> libc.so -> app
would suffice. Having the '-la' in libb.la and '-lb' in libc.la would
cause a tree like
---------------------------
/ ,---------------- \
/ / `v v
liba.so -> libb.so -> libc.so -> app
\ ^
`----------------'
Unfortunately, widely used tools like 'libtool' or 'cmake' are creating
such trees (at least when the libs and apps are in the same project). For
'cmake' there is a workaround to put '-Wl,--as-needed' into the linker
flags but for 'libtool' you have to patch ltmain.
A good check to verify cleaness of libraries/binaries is
| ldd -u -r <lib>
This should neither output undefined symbols nor unused direct dependencies.
> From a different view: *.la files aren't much different than *.pc
> files, in fact they contain a subset of their information.
ACK. Often, 'pkgconfig' is used wrongly and contains superflous Requires:
resulting into a tree like above.
'pkgconfig' might make sense in providing certain C(PP)FLAGS; but .la
files are completely superflous (at least for for dynamic linking).
Enrico
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