Messages in this thread | | | Date | Mon, 23 Jun 2008 11:04:57 -0700 | From | Mike Travis <> | Subject | Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area |
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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.
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