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SubjectRe: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area
Mike Travis wrote:
> Eric W. Biederman wrote:
>
>> Mike Travis <travis@sgi.com> writes:
>>
> ...
>
>>> 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
>>
>
> FYI, I did try this out and it caused the bootloader to scramble the
> loaded data. The first corruption I found was the .x86cpuvendor.init
> section contained all zeroes.

Well, that's what appeared to be happening with the pre-initialized GDT
as well, so I'm not sure that's a new symptom.

J


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