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SubjectRe: [PATCH v3 4/8] powerpc/vdso32: inline __get_datapage()
Date
Michael Ellerman <mpe@ellerman.id.au> writes:
> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>> __get_datapage() is only a few instructions to retrieve the
>> address of the page where the kernel stores data to the VDSO.
>>
>> By inlining this function into its users, a bl/blr pair and
>> a mflr/mtlr pair is avoided, plus a few reg moves.
>>
>> The improvement is noticeable (about 55 nsec/call on an 8xx)
>>
>> vdsotest before the patch:
>> gettimeofday: vdso: 731 nsec/call
>> clock-gettime-realtime-coarse: vdso: 668 nsec/call
>> clock-gettime-monotonic-coarse: vdso: 745 nsec/call
>>
>> vdsotest after the patch:
>> gettimeofday: vdso: 677 nsec/call
>> clock-gettime-realtime-coarse: vdso: 613 nsec/call
>> clock-gettime-monotonic-coarse: vdso: 690 nsec/call
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>
> This doesn't build with gcc 4.6.3:
>
> /linux/arch/powerpc/kernel/vdso32/gettimeofday.S: Assembler messages:
> /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:41: Error: unsupported relocation against __kernel_datapage_offset
> /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:86: Error: unsupported relocation against __kernel_datapage_offset
> /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:213: Error: unsupported relocation against __kernel_datapage_offset
> /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:247: Error: unsupported relocation against __kernel_datapage_offset
> make[4]: *** [arch/powerpc/kernel/vdso32/gettimeofday.o] Error 1

Actually I guess it's binutils, which is v2.22 in this case.

Needed this:

diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
index 12785f72f17d..0048db347ddf 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -117,7 +117,7 @@ extern struct vdso_data *vdso_data;
.macro get_datapage ptr, tmp
bcl 20, 31, .+4
mflr \ptr
- addi \ptr, \ptr, __kernel_datapage_offset - (.-4)
+ addi \ptr, \ptr, (__kernel_datapage_offset - (.-4))@l
lwz \tmp, 0(\ptr)
add \ptr, \tmp, \ptr
.endm

cheers

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