Date: Sat, 13 Apr 2002 01:00:34 -0600 (MDT) From: "M. Warner Losh" <imp@village.org> To: roam@ringlet.net Cc: dima@sinp.msu.ru, freebsd-hackers@FreeBSD.ORG Subject: Re: dynamic libraries Message-ID: <20020413.010034.64370390.imp@village.org> In-Reply-To: <20020413095747.E352@straylight.oblivion.bg> References: <20020413092834.A352@straylight.oblivion.bg> <20020413.004859.00083529.imp@village.org> <20020413095747.E352@straylight.oblivion.bg>
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In message: <20020413095747.E352@straylight.oblivion.bg>
Peter Pentchev <roam@ringlet.net> writes:
: On Sat, Apr 13, 2002 at 12:48:59AM -0600, M. Warner Losh wrote:
: > In message: <20020413092834.A352@straylight.oblivion.bg>
: > Peter Pentchev <roam@ringlet.net> writes:
: > : On Fri, Apr 12, 2002 at 10:09:16PM -0600, M. Warner Losh wrote:
: > : > In message: <Pine.BSF.4.43.0204121308470.4449-100000@BigKing.sinp.msu.ru>
: > : > Dmitry Mottl <dima@sinp.msu.ru> writes:
: > : > : How can I link C program with different versions of the same library?
: > : >
: > : > You can't.
: > :
: > : Okay; what exactly is it that you cannot do - link a program against
: > : two versions of the same library simultaneously (I thought so), or
: > : link a program against a *specified* version of a library (what, I think,
: > : the original poster clarifies he wants to do, for no specific reason)?
: >
: > You can't, generally, link against two different versions of the same
: > library. The reason is that you get mutiply defined symbols because
: > it is very very very rare that two different versions of the same
: > library wouldn't have any symbols that overlap.
:
: Well, actually, your 'full path' suggestion gave me an idea..
:
: [roam@straylight:p6 ~/c/misc/foo]$ cc -o foo18 foo18.c /usr/lib/libncurses.so.5 /usr/lib/compat/libncurses.so.3
: [roam@straylight:p6 ~/c/misc/foo]$ ldd ./foo18
: ./foo18:
: libncurses.so.5 => /usr/lib/libncurses.so.5 (0x28065000)
: libncurses.so.3 => /usr/lib/compat/libncurses.so.3 (0x280a7000)
: libc.so.4 => /usr/lib/libc.so.4 (0x280b8000)
: libmytinfo.so.2 => /usr/lib/compat/libmytinfo.so.2 (0x28151000)
: [roam@straylight:p6 ~/c/misc/foo]$
:
: Duplicate symbols are not a problem - AFAIK, symbols are resolved
: in the order the libraries were specified on the linker command line,
: and, consequently, in the order the dependencies are recorded into
: the resulting executable file. So, if foo18 calls an ncurses.5 routine,
: it will be invoked from ncurses.5; if foo18 calls a routine that is
: not present in ncurses.5, it will be invoked from ncurses.3.
:
: So it is actually possible; not that I have ANY idea what the point
: would be..
Ah, this just hides the problem of incompatible interfaces :-(.
that's why the libraries have different version numbers: they have a
different API.
Warner
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