Date: Tue, 22 Dec 2015 15:59:20 -0800 From: Arlie Stephens <arlie@worldash.org> To: hackers@FreeBSD.ORG Subject: Examining Page Tables in Kernel Crash Dumps (amd64) Message-ID: <20151222235920.GA21736@worldash.org>
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I'm chasing a bug in an elderly, customized freebsd kernel that appears to result in corrupted page tables. kgdb is not cooperating when I attempt to look at addresses of kernel page tables. I've replicated that part on an elderly stock freebsd system, running freebsd 8.4. , and it looks to me like it's probably getting that limitation from libkvm. Obviously I don't expect community help with an ancient freebsd issue... particularly one probably caused by our own customizations. But given the tool chain changes upstream, I don't expect testing with whatever kgdb has turned into there to be very relevant ;-( So far, the only way I know to get a look at kernel page table contents in FreeBSD is on live systems with ddb. I would like to know whether there are any tools I haven't noticed for dealing with page tables in crash dumps - or, for that matter, whether kgdb is supposed to be able to display the kernel's recursive page tables. Failing that, I may just have to write one ;-) (Or figure out how to chase my problem on live systems.) -- Arlie (Arlie Stephens arlie@worldash.org)
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