[U-Boot] Weak symbols: request for comments

[Sebastien Carlier]

Dear Reinhard,

On 11/05/2010 12:16 PM, Reinhard Meyer wrote:
>> 1.2) Use regular (non-weak) extern declarations for overridable stuff;
>>        collect all default weak symbols into a separate library archive,
>>        to be supplied last to the linker.
>>      
> Not very practical, that would require that each driver etc. would
> be in two parts, the main part and the "weak" part. It would no need
> weak functions, however.
>    

You are entirely correct.  It would be slightly inconvenient for drivers 
that provide overridable stuff, but no non-standard feature is needed 
and the benefit of static linking is preserved.

>> 1.3) Stop using a library archive for the board specific stuff.
>>        Instead, collect and link all the object files to produce the
>>        output binary.  Only Makefile changes are involved, but correct
>>        behavior depends on all boards doing the right thing.
>>      
> I don't like the "weak" concept :)
>    

It does seem like weak symbols were designed with other uses in mind, 
such as C++ class members defined within a class declaration, or to weak 
the dependencies between libraries... but not really to allow 
overridable definitions (what if two objects want to override the same 
weak symbol in different ways?).

>> 1.4) Link u-boot into a board-agnostic dynamic library, link the
>>        board-specific stuff into an executable embedding a dynamic
>>        linker, and package all this stuff somehow.
>>      
> That is too complex. Besides there are few board-agnostic parts in
> u-boot, many functions rely in included defines that are board
> specific.
>    

Agreed.

>> Are there better options?  Which one would you prefer to see
>> implemented?
>>      
> Yes. The old-fashioned #define CONFIG_BOARD_INIT_F and friends
> method. I would prefer that one. Its not beautiful but still
> widely used and bullet-proof.
>    

Could you please elaborate?  I have looked for things like this in the 
code base but I could not find what you are referring to.

Regards,

Sebastien Carlier