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

From: Laszlo Ersek
Subject: Re: [Qemu-devel] dump-guest-memory command?
Date: Fri, 16 May 2014 17:38:03 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

On 05/16/14 15:01, Jun Koi wrote:
> On Fri, May 16, 2014 at 7:30 PM, Laszlo Ersek <address@hidden
> <mailto:address@hidden>> wrote:
>     On 05/16/14 11:59, Jun Koi wrote:
>     > - is it true that dump-guest-memory just write down physical memory
>     > page, and does not consider the virtual-memory concept?
>     No, it isn't.
>     Basically, "dump-guest-memory" supports two modes of operation, "paging
>     enabled" and "paging disabled".
>     Many (most?) people dump for the "crash" utility, which is super smart,
>     and extra paging info is not needed. For "crash" we just dump the
>     guest-phys memory ranges the way the guest sees them, and that's it;
>     "crash" figures out everything from that.
>     If you want to use "gdb" rather than "crash", or need the guest-virtual
>     addresses in the ELF vmcore for some other reason, then you should
>     invoke "dump-guest-memory" with paging enabled.
>     Enter "help dump-guest-memory" at the qemu monitor prompt, and look for
>     the "-p" option.
> so i suppose this works for all kind of OS in guest VM, not only Linux
> guest?

far as I remember, it should; the virtual mappings "in effect" are
searched starting from cr3:

qmp_dump_guest_memory() [dump.c]
    qemu_get_guest_memory_mapping() [memory_mapping.c]
      for (almost) all VCPUs:
        cpu_get_memory_mapping() [qom/cpu.c]
            check cr3, cr4; walk page tables etc

There are some caveats / limitations: search "qapi-schema.json" for the
string "dump-guest-memory", and read that section.


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