55 lines
1.9 KiB
ReStructuredText
55 lines
1.9 KiB
ReStructuredText
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=================
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VMCoreInfo device
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=================
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The ``-device vmcoreinfo`` will create a ``fw_cfg`` entry for a guest to
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store dump details.
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``etc/vmcoreinfo``
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==================
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A guest may use this ``fw_cfg`` entry to add information details to QEMU
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dumps.
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The entry of 16 bytes has the following layout, in little-endian::
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#define VMCOREINFO_FORMAT_NONE 0x0
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#define VMCOREINFO_FORMAT_ELF 0x1
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struct FWCfgVMCoreInfo {
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uint16_t host_format; /* formats host supports */
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uint16_t guest_format; /* format guest supplies */
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uint32_t size; /* size of vmcoreinfo region */
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uint64_t paddr; /* physical address of vmcoreinfo region */
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};
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Only full write (of 16 bytes) are considered valid for further
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processing of entry values.
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A write of 0 in ``guest_format`` will disable further processing of
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vmcoreinfo entry values & content.
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You may write a ``guest_format`` that is not supported by the host, in
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which case the entry data can be ignored by QEMU (but you may still
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access it through a debugger, via ``vmcoreinfo_realize::vmcoreinfo_state``).
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Format & content
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================
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As of QEMU 2.11, only ``VMCOREINFO_FORMAT_ELF`` is supported.
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The entry gives location and size of an ELF note that is appended in
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qemu dumps.
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The note format/class must be of the target bitness and the size must
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be less than 1Mb.
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If the ELF note name is ``VMCOREINFO``, it is expected to be the Linux
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vmcoreinfo note (see `the kernel documentation for its format
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<https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-kernel-vmcoreinfo>`_).
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In this case, qemu dump code will read the content
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as a key=value text file, looking for ``NUMBER(phys_base)`` key
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value. The value is expected to be more accurate than architecture
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guess of the value. This is useful for KASLR-enabled guest with
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ancient tools not handling the ``VMCOREINFO`` note.
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