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SubjectRe: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area
Mike Travis <travis@sgi.com> writes:

> Jeremy Fitzhardinge wrote:
>>
>>
>> BTW, I think __per_cpu_load will cause trouble if you make a relocatable
>> kernel, being an absolute symbol. But I have relocation off at the moment.
>>
> ...
> Here's where it's defined (in include/asm-generic/vmlinux.lds.h):
>
> #ifdef CONFIG_HAVE_ZERO_BASED_PER_CPU
> #define PERCPU(align) \
> . = ALIGN(align); \
> percpu : { } :percpu \
> __per_cpu_load = .; \
> .data.percpu 0 : AT(__per_cpu_load - LOAD_OFFSET) { \
> *(.data.percpu.first) \
> *(.data.percpu.shared_aligned) \
> *(.data.percpu) \
> *(.data.percpu.page_aligned) \
> ____per_cpu_size = .; \
> } \
> . = __per_cpu_load + ____per_cpu_size; \
> data : { } :data
> #else
>
> Can we generate a new symbol which would account for LOAD_OFFSET?

Ouch. Absolute symbols indeed. On the 32bit kernel that may play havoc
with the relocatable kernel, although we have had similar absolute logic
for the last year. With __per_cpu_start and __per_cpu_end so it may
not be a problem.

To initialize the percpu data you do want to talk to the virtual address
at __per_coup_load. But it is absolute Ugh.

It might be worth saying something like.
.data.percpu.start : AT(.data.percpu.dummy - LOAD_OFFSET) {
DATA(0)
. = ALIGN(align);
__per_cpu_load = . ;
}
To make __per_cpu_load a relative symbol. ld has a bad habit of taking
symbols out of empty sections and making them absolute. Which is why
I added the DATA(0).

Still I don't think that would be the 64bit problem.

Eric



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