Date: Tue, 04 Aug 2015 17:09:39 -0700 From: John Baldwin <jhb@freebsd.org> To: John-Mark Gurney <jmg@funkthat.com> Cc: 'freebsd-arch' <freebsd-arch@freebsd.org> Subject: Re: Supporting cross-debugging vmcores in libkvm Message-ID: <2016463.jQeq4BdiyV@ralph.baldwin.cx> In-Reply-To: <20150804190058.GM78154@funkthat.com> References: <3121152.ujdxFEovO3@ralph.baldwin.cx> <20150804190058.GM78154@funkthat.com>
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On Tuesday, August 04, 2015 12:00:59 PM John-Mark Gurney wrote: > John Baldwin wrote this message on Tue, Aug 04, 2015 at 10:56 -0700: > > Many debuggers (recent gdb and lldb) support cross-architecture debugging > > just fine. My current WIP port of kgdb to gdb7 supports cross-debugging for > > remote targets already, but I wanted it to also support cross-debugging for > > vmcores. > > Have you looked at the work the my GSoC student, Daniel Lovasko, is > doing: > https://wiki.freebsd.org/SummerOfCode2015/TypeAwareKernelVirtualMemoryAccess > > This uses libctf to completely abstract out the accessing of data > in libkvm so that it can be used w/ any arch as long as you have ctf > data... This means you could use netstat on amd64 on an armeb vmcore > w/o issues... > > It does look like some of this is still useful, but want to make sure > that we aren't reproducing tons of work... > > For example, he's working on procstat right now: > https://github.com/lovasko/taprocstat That doesn't seem to address the need of how you parse the actual vmcore file itself to resolve a virtual address to a location in the vmcore file. (e.g. on "plain" dumps on i386 this means walking the page tables whereas for minidumps it means parsing a special set of PTEs and bitmap at the start of the file). To be clear, all that my work enables is doing a kvm_read() of a foreign vmcore. All the logic to decide how many bytes to read and at what address (and then decoding those appropriately) happens in the debugger (gdb/lldb, etc.). The project here seems to be using CTF instead of dwarf to do the sort of things the debugger does when you 'p *foo', but you still need a way to find the 'foo' in the vmcore file. -- John Baldwin
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