Re: [Qemu-devel] dump-guest-memory command?

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Fri, 16 May 2014 16:40:23 +0800
Jun Koi <junkoi2004@gmail.com> wrote:
> On Fri, May 16, 2014 at 3:03 PM, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
> 
> > On Fri, 16 May 2014 14:24:16 +0800
> > Jun Koi <junkoi2004@gmail.com> wrote:
> > > Hi,
> > >
> > > Anybody please help me on this dump-guest-memory command? How does the
> > > virtual memory map to the dumped file?
> > >
> > > For example, if x86 register RIP points to 0x12345, how does that map to
> > > the dump file? Meaning how can I find where this address 0x12345 in the
> > > dump?
> > >
> > > I tried, but couldnt find much documentation on this command.
> > >
> > > Thank you a lot,
> > > Jun
> >
> > Hi Jun,
> >
> > The dump file is in ELF format and data is written in ELF notes.
> > Use readelf -a on the file and you'll get something like the
> > following at the end of the output:
> >
> > ...
> >
> > Notes at offset 0x000001c8 with length 0x00000328:
> >   Owner                 Data size       Description
> >   CORE                 0x00000150       NT_PRSTATUS (prstatus structure)
> >   QEMU                 0x000001b0       Unknown note type: (0x00000000)
> >
> > The registers sit in the NT_PRSTATUS note (hence somewhere offset
> > 0x000001c8 and 0x000001c8+0x00000150+0x14 (the latter is the ELF note
> > header size). Be aware that intel is little endian: if RIP is 0x00012345,
> > you need to look for '45 23 01 00' in the file.
> >
> >
> Thanks so much, but perhaps you misunderstood my question? What I want to
> know is how to map 0x12345 (virtual address) back to the dump file.
> 

Heh... sorry for that, morning isn't the best time to answer questions I guess ;)

> For example, if 0x12345 was executing some filesystem code at the time I
> dumped the VM, then I can locate exactly that code in the dumpfile, thanks
> to the given RIP address (which is 0x12345 in this example)
> 
> I hope I explain my idea clear enough this time?
> 

Yeah. Maybe the crash utility (http://people.redhat.com/anderson) can help.

> Thanks a lot,
> Jun



-- 
Gregory Kurz                                     kurzgreg@fr.ibm.com
                                                 gkurz@linux.vnet.ibm.com
Software Engineer @ IBM/Meiosys                  http://www.ibm.com
Tel +33 (0)562 165 496

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