Messages in this thread | | | From | Kazuhito Hagio <> | Subject | RE: [PATCH v2] x86_64, vmcoreinfo: Append 'page_offset_base' to vmcoreinfo | Date | Mon, 19 Nov 2018 21:07:27 +0000 |
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On 11/15/2018 4:47 PM, Bhupesh Sharma wrote: > Adding 'page_offset_base' to the vmcoreinfo can be specially useful for > live-debugging of a running kernel via user-space utilities > like makedumpfile (see [1]).
I agree.
> Recently, I saw an issue with the 'makedumpfile' utility (see [2] for > details), whose live debugging feature is broken with newer kernels > (I tested the same with 4.19-rc8+ kernel), as KCORE_REMAP segments were > added to kcore, thus leading to an additional sections in the same, and > makedumpfile is not longer able to determine the start of direct > mapping of all physical memory, as it relies on traversing the PT_LOAD > segments inside kcore and using the last PT_LOAD segment > to determine the start of direct mapping.
Actually, the KCORE_REMAP segments were already removed from kcore by commit bf904d2762ee ("x86/pti/64: Remove the SYSCALL64 entry trampoline") and kcore's program headers got back to the previous ones, but this fact shows that they are changeable.
So I think that if we have this NUMBER(page_offset_base) in vmcoreinfo for x86_64, user-space tools (especially makedumpfile) would become more stable against changes in kcore and vmcore, rather than depending on their PT_LOAD values.
Thanks, Kazu
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