maria-discuss team mailing list archive

[Arjen Lentz <arjen@xxxxxxxxxxxxx>]

Hi Vlad, all

On 28/03/2011, at 8:18 AM, Vladislav Vaintroub wrote:
> For 5.5  the discussion starts here http://bugs.mysql.com/bug.php?id=59078
> ([9 Feb 2:26] Clint Byrum, IIRC he works for Debian). His argument  
> that ABI
> has changed "dramatically" is  that for example an exported symbol  
> named
> TERMINATE has  gone, while new symbols PSI_hook and PSI_server were  
> added.
> He uses "nm" for his argumentation.
>
> Clint's claim is that every time an exported symbol is changed/ 
> removed or
> added, shared library version must be bumped. Unix linkers  export  
> every
> global function and variable  by default. Which means, if one  
> renames a
> global variable as part of cleanup, the ABI is changed.  Changes  
> like that
> can happen really in any point  release, so I see no other way to  
> maintain
> the 100% ABI  compatibility, rather than restricting  visibility  to  
> only
> symbols defined by client API (i.e mysql_xxx stuff) . On some  
> Unixes, it is
> possible to do with  linker version script .On Windows symbols were
> restricted to the official API from the start on , using with  
> the .def file.
>
>
> This would be a clean solution from my point of view. However,  
> should we go
> for it,  this would result in incompatibilities with Oracle's MySQL,  
> and
> this has to be worked out somehow (best thing is probably contribute
> visibility-restricting patch, if they are at all interested) .


I think it makes sense to use a linker version script just like  
using .def on Windows.
There's a clearly defined (and documented) set of functions and  
variables, and nothing else should be exposed.

Obviously if some environments don't support doing this for a library  
then there's not much we can do (apart from not having global  
variables! ;-) but otherwise it works out fine and also satisfies  
Clint's concerns. I figure libmysqlclient is not the only thing Debian  
has reviewed, so apparently the many other libraries do apply a  
methodology that restricts undesired symbol exposure.

So, no need to invent the wheel there; if others do this, it'll be  
plainly visible. Look at another library and see how it's done there.
Do the same and indeed let's submit that cleanup back to Oracle in a  
public bugreport.


> Besides ,
> Unix users  need to be warned that shared and static library are not
> interchangeable and that it will not be possible to access e.g
> mysys/strings/dbug functionality using the shared library. Hopefully  
> most of
> the programs are written using officially documented client API  
> functions,
> so there won't be many surprises.

They should, otherwise all kinds of things can go wrong anyway.

Regards,
Arjen.
--
Arjen Lentz, Exec.Director @ Open Query (http://openquery.com)
Remote expertise & maintenance for MySQL/MariaDB server environments.

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