Re: having trouble making my version of pthread_condattr_init/destroy visible to outside world

[Daniel De La Zerda <ddelazerda007 at yahoo dot com>]

>If you strong alias pthread_foocondattr_init to pthread_condattr_init
>then your entry point is now pthread_condattr_init, not
>pthread_foocondattr_init.

I strong alias'ed __pthread_foocondattr_init to pthread_foocondattr_init.

>Did you perform hidden_proto(pthread_foocondattr_init) on the
>prototype definition and hidden_def(pthread_foocondattr_init) on the
>implementation?  If so then you've asked the compiler to hide the
>internal symbol name.

No. I have not used hidden_proto() nor hidden_def().

>If you look at the addresses in objdump of pthread_condattr_init and
>pthread_foocondattr_init they should have the same address.

Yes, when I do "nm libpthread.so | grep pthread_foocondattr_init", both "pthread_foocondattr_init" and "__pthread_foocondattr_init" show up with the same address but both have a "t" besides them, whereas I was expecting "pthread_minicondattr_init" to have a "T" besides it - be globally visible.




----- Original Message ----
From: Ryan Arnold <ryan.arnold@gmail.com>
To: Daniel De La Zerda <danieldelazerda@gmail.com>
Cc: Carlos O'Donell <carlos@systemhalted.org>; libc-help@sourceware.org
Sent: Wednesday, April 15, 2009 2:40:00 PM
Subject: Re: having trouble making my version of pthread_condattr_init/destroy  visible to outside world

On Wed, Apr 15, 2009 at 1:16 PM, Daniel De La Zerda
<ddelazerda007@yahoo.com> wrote:
>
> Hi, I have my versions of the pthread_foocondattr_init/destroy functions and when I compile code using them I get "undefined reference" errors. I have added these two functions inside the nptl/Versions file. At the bottom of their function definition files I added strong_alias() following the same convention as in the regular pthread_condattr_init/destroy. Their symbols get exported but both symbols __pthread_foocondattr_init/destroy and pthread_foocondattr_init/destroy show with a small "t" next to their names. I was expecting the pthread_foocondattr_init/destroy symbol should have "T" which then would mean that their are visible to the outside world. On the other hand the pthread_condattr_init/destroy functions that come with glibc do show up with "T".

If you look at the addresses in objdump of pthread_condattr_init and
pthread_foocondattr_init they should have the same address.

Did you perform hidden_proto(pthread_foocondattr_init) on the
prototype definition and hidden_def(pthread_foocondattr_init) on the
implementation?  If so then you've asked the compiler to hide the
internal symbol name.

If you strong alias pthread_foocondattr_init to pthread_condattr_init
then your entry point is now pthread_condattr_init, not
pthread_foocondattr_init.

This is often done for three reasons:

1.) To allow different backend implementations to have a common front-end.
2.) To allow GLIBC to internally invoke the internal symbol without
going through the PLT, i.e. static function invocation.
3.) strong-alias disallows external override of the internal
implementation, meaning if you don't want the user to override the
internal implementation you can use a strong alias.

Perhaps a relevant snippet of your header file and implementation
would be in order.

Ryan