linux-kernel - Re: V4L2: __ucmpdi2 undefined on ppc

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Date:	Sat, 16 Dec 2006 16:15:12 -0200
From:	Mauro Carvalho Chehab <mchehab@...radead.org>
To:	Kyle McMartin <kyle@...ntu.com>
Cc:	Meelis Roos <mroos@...ux.ee>,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: V4L2: __ucmpdi2 undefined on ppc

> I posted a patch to Paul this week to fix this, as saw we saw it on
> Ubuntu's powerpc kernel builds.
> 
> Since ppc32 can't do a 64bit comparison on its own it seems, gcc
> will generate a call to a helper function from libgcc. What other
> arches do is link libgcc.a into libs-y, and export the symbol
> they want from it. The build process will discard the rest of the
> .a that is unused. parisc uses this method, for example.
> 
> Gcc targets can provide optimized versions of these helpers in
> assembly, but at least in this case, the generic C version seems
> to be used everywhere. It might be useful to provide kernel local
> copies of these C versions linked __weak or something if the
> arch happens to need them.
> 
> (Not going to sign off or anything, since I've already sent it to
> paulus@ and I don't want it to get merged without his approval...)

Seems to be a good way to solve it.


> ---
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index a00fe72..5b60c05 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -139,6 +139,8 @@ core-$(CONFIG_XMON)		+= arch/powerpc/xmon/
>  
>  drivers-$(CONFIG_OPROFILE)	+= arch/powerpc/oprofile/
>  
> +libs-y				+= `$(CC) -print-libgcc-file-name`
> +
>  # Default to zImage, override when needed
>  defaultimage-y			:= zImage
>  defaultimage-$(CONFIG_PPC_ISERIES) := vmlinux
> diff --git a/arch/powerpc/kernel/ppc_ksyms.c b/arch/powerpc/kernel/ppc_ksyms.c
> index 9179f07..dea8384 100644
> --- a/arch/powerpc/kernel/ppc_ksyms.c
> +++ b/arch/powerpc/kernel/ppc_ksyms.c
> @@ -164,6 +164,9 @@ long long __lshrdi3(long long, int);
>  EXPORT_SYMBOL(__ashrdi3);
>  EXPORT_SYMBOL(__ashldi3);
>  EXPORT_SYMBOL(__lshrdi3);
> +
> +extern void __ucmpdi2(void);
> +EXPORT_SYMBOL(__ucmpdi2);
>  #endif
>  
>  EXPORT_SYMBOL(memcpy);
> -
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Cheers, 
Mauro.

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