[U-Boot] [PATCH] ppc4xx: Add Sequoia RAM-booting target

[Stefan Roese]

On Thursday 07 May 2009, Detlev Zundel wrote:
> >> If so, it still seems to be a somewhat rude way to do it.  How
> >> long will it take the gcc maintainers to produce a "warning: unused
> >> variable is used" warning? ;)
> >
> > I prefer to do it this way instead of encasing the variable declaration
> > into another #ifdef ... #endif section. This is used in many cases in the
> > Linux kernel btw. Here the macro "__maybe_unsed" is defined to
> > "__attribute__((unused))".
>
> In many cases?  a rgrep on a recent kernel counts 84 incantations, which
> is not much for the Linux kernel, I believe.

Perhaps it's quite new to the Linux kernel. I just spotted it the first time a 
few weeks ago and thought: "What a nice way to remove some of the ugly 
#ifdef's in U-Boot!". :)

> > So what should I do now? Should I revert to another #ifdef in the
> > variable declaration? Or is the current version ok?
>
> I'm not too sure myself.  What really tickles me, and what speaks
> against using this attribute, is the fact that the "unused" attribute is
> itself not part of an #ifdef, whereas the intention clearly is that this
> attribute should only be applied when the ifdefs erases code.

BTW: The resulting code/data length is the same, comparing a version with 
#ifdef's, the attribute version or a version with the variable declaration 
intact and the warnings.

> Now currently this connection maybe clear for the writer of the patch,
> but it is in no way obvious in the code.  So theoretically, when the
> #ifdef gets removed, nobody will think about the "unused" attributes,
> forget them and then we have effectively lost correct warnings.

This could be the case. But this could happen to the #ifdef version as well. 
That the #ifdef'ed variable declaration stays in the code after removing the 
code referencing the variables.

Best regards,
Stefan

=====================================================================
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: +49-8142-66989-0 Fax: +49-8142-66989-80  Email: office at denx.de
=====================================================================