lkml.org 
[lkml]   [2008]   [Jun]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area
Jeremy Fitzhardinge wrote:
> Mike Travis wrote:
>> Eric W. Biederman wrote:
>>
>>> 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
>>>
>>
>> I'm not sure I understand the linker lingo enough to fill in the rest
>> of the blanks... I've tried various versions around this framework and
>> none have been accepted yet.
>>
>> #ifdef CONFIG_HAVE_ZERO_BASED_PER_CPU
>> #define PERCPU(align) \
>> .data.percpu.start : AT(.data.percpu.dummy - LOAD_OFFSET) { \
>> DATA(0) \
>> . = ALIGN(align); \
>> __per_cpu_load = .; \
>> *(.data.percpu.first) \
>> *(.data.percpu.shared_aligned) \
>> *(.data.percpu) \
>> *(.data.percpu.page_aligned) \
>> ____per_cpu_size = . - __per_cpu_load \
>> } \
>> #else
>>
>
> That looks OK to me. Does it work?
>
> J

Nope, fighting undefines and/or syntax errors in the linker.


\
 
 \ /
  Last update: 2008-06-23 20:07    [W:0.296 / U:1.156 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site