Messages in this thread |  | | | Date | Mon, 23 Jun 2008 13:33:52 -0400 | | From | Jeremy Fitzhardinge <> | | Subject | Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area |
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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
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