Re: [Bug 11800] New: building SES support fails w/ gcc-3.4.5

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Thu, 2008-10-23 at 12:14 -0400, Marc Bejarano wrote:
> At 17:17 10/22/2008, James Bottomley wrote:
>  >On Wed, 2008-10-22 at 13:30 -0700, Andrew Morton wrote:
>  >> OK, it's here:
>  >>
>  >> 	buf = kmalloc(vpd_len, GFP_KERNEL);
>  >>
>  >> it's a gcc bug.
>  >>
>  >> Please see if you can find some way to make it go away - perhaps change
>  >> vpd_len's type to `int', things like that.
>  >>
>  >> Or use a different compiler version :(
> 
> i'm not worried about compiling this.  i already did a compilation 
> without it and i'll be fine without SES.  i just selected it on the 
> off chance i'd find time to play with it.  i was just doing my duty 
> of reporting this to save others the trouble.
> 
>  >Could it be an optimisation issue?  The static oversize test relies on
>  >the compiler optimising away a leg that can never be reached if the size
>  >is under the max. If you do a make V=1 you'll see what optimisation
>  >flags the compiler is using ... if it's -O2 then yes, the compiler
>  >should be optimising stuff away and it's a clear compiler problem.  If
>  >it's anything else, we might have a mis setting of the optimisation
>  >level in the kernel build.
> 
> looks to me like -Os:

I think we have a winner: -Os is rather less well implemented in older
versions of gcc.  Could you retry with -O2?

You do this by setting the config option

CONFIG_CC_OPTIMIZE_FOR_SIZE

to N (it defaults to Y).  If we verify this to be the root cause, we
might consider making the default for that option N if gcc version is <
4.

James