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SubjectRe: [PATCH] Compile failure fix for ppc on 2.6.17-rc4-mm3 (2nd attempt) (Mel Gorman) wrote:
> (Resending with Andrew's email address correct this time)
> For the last few -mm releases, kernels built for an old RS6000 failed to
> compile with the message;
> arch/powerpc/kernel/built-in.o(.init.text+0x77b4): In function `vrsqrtefp':
> : undefined reference to `__udivdi3'
> arch/powerpc/kernel/built-in.o(.init.text+0x7800): In function `vrsqrtefp':
> : undefined reference to `__udivdi3'
> make: *** [.tmp_vmlinux1] Error 1

A function with a name like that doesn't _deserve_ to compile.

But actually vrsqrtefp() doesn't call __udivdi3 - the error lies somewhere
else in the kernel and the toolchain gets it wrong, so we don't know where.

The way I usually hunt this problem down is to build the .s files (make
arch/powerpc/kernel/foo.s) and then grep around, find the offending C

If the problem is specific to powerpc then a

diffstat 2.6.17.rc4-mm3 | grep powerpc

will narrow down the number of files to be searched by rather a lot.

> 2.6.17-rc5 is not affected but I didn't search for the culprit patch in
> -mm. The following patch adds an implementation of __udivdi3 for plain old
> ppc32. This may not be the correct fix as Google tells me that __udivdi3
> has been replaced by calls to do_div() in a number of cases. There was no
> obvious way to do that for vrsqrtefp, hence this workaround. The patch should
> be acked, rejected or replaced by a ppc expert.

Yes, we've traditionally avoided adding the 64-bit divide library functions.
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