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RE: GNU libc confusion with symbols undefined.



Dave so essentially @@GLIBC_2.2.5 is the symbol version set this release is based on? Not necessarily having anything to do with the underlying RPM package version? This is what I'm getting from your explanation.

One question I'm still uncertain about is why do these symbols still show up as undefined?


-----Original Message-----
From: fedora-devel-list-bounces redhat com [mailto:fedora-devel-list-bounces redhat com] On Behalf Of David Malcolm
Sent: Friday, September 18, 2009 10:54 AM
To: Development discussions related to Fedora
Subject: Re: GNU libc confusion with symbols undefined.

On Fri, 2009-09-18 at 09:21 -0500, Brown, Rodrick wrote:
> I'm trying to understand the following here
>
> I have a simple test program that calls memcpy/malloc/printf
>
> int
> main(int argc, char **argv)
> {
>  char * p = malloc(10);
>  memcpy(p,"Hello",6);
>  printf("%s\n", p);
> }
>
> When looking at the symbol list why are the following routines undefined? And why is it referncing GLIBC_2.2.5?
>
> $ nm /tmp/f |grep ' U '
>                  U __libc_start_main@@GLIBC_2.2.5
>                  U malloc@@GLIBC_2.2.5
>                  U memcpy@@GLIBC_2.2.5
>                  U printf@@GLIBC_2.2.5
>
> $ rpm -qa |grep -i glibc
> glibc-2.3.4-2.41
> glibc-common-2.3.4-2.41
> glibc-2.3.4-2.41
>
> I really can't find an explination for this and was wondering if someone could clear it up.

libc has "versioned symbols", and you're linking against the default implementations of each of the three symbols, as defined in the version of libc you built against (the "@@" notation means the default version of a versioned symbol).

For detailed information on this, see:
http://people.redhat.com/drepper/dsohowto.pdf
and for the most detail, see:
http://people.redhat.com/drepper/symbol-versioning


Hope this helps
Dave

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