Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 20 Jun 2008 13:25:06 -0700 | Subject | Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area |
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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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