[qemu.git] / docs / specs / vmcoreinfo.txt

=================
VMCoreInfo device
=================

The `-device vmcoreinfo` will create a fw_cfg entry for a guest to
store dump details.

etc/vmcoreinfo
**************

A guest may use this fw_cfg entry to add information details to qemu
dumps.

The entry of 16 bytes has the following layout, in little-endian::

#define VMCOREINFO_FORMAT_NONE 0x0
#define VMCOREINFO_FORMAT_ELF 0x1

    struct FWCfgVMCoreInfo {
        uint16_t host_format;  /* formats host supports */
        uint16_t guest_format; /* format guest supplies */
        uint32_t size;         /* size of vmcoreinfo region */
        uint64_t paddr;        /* physical address of vmcoreinfo region */
    };

Only full write (of 16 bytes) are considered valid for further
processing of entry values.

A write of 0 in guest_format will disable further processing of
vmcoreinfo entry values & content.

You may write a guest_format that is not supported by the host, in
which case the entry data can be ignored by qemu (but you may still
access it through a debugger, via vmcoreinfo_realize::vmcoreinfo_state).

Format & content
****************

As of qemu 2.11, only VMCOREINFO_FORMAT_ELF is supported.

The entry gives location and size of an ELF note that is appended in
qemu dumps.

The note format/class must be of the target bitness and the size must
be less than 1Mb.

If the ELF note name is "VMCOREINFO", it is expected to be the Linux
vmcoreinfo note (see Documentation/ABI/testing/sysfs-kernel-vmcoreinfo
in Linux source). In this case, qemu dump code will read the content
as a key=value text file, looking for "NUMBER(phys_base)" key
value. The value is expected to be more accurate than architecture
guess of the value. This is useful for KASLR-enabled guest with
ancient tools not handling the VMCOREINFO note.
Commit	Line	Data
6e43353f MAL	1	=================
	2	VMCoreInfo device
	3	=================
	4
	5	The `-device vmcoreinfo` will create a fw_cfg entry for a guest to
	6	store dump details.
	7
	8	etc/vmcoreinfo
	9	**************
	10
	11	A guest may use this fw_cfg entry to add information details to qemu
	12	dumps.
	13
	14	The entry of 16 bytes has the following layout, in little-endian::
	15
	16	#define VMCOREINFO_FORMAT_NONE 0x0
	17	#define VMCOREINFO_FORMAT_ELF 0x1
	18
	19	struct FWCfgVMCoreInfo {
	20	uint16_t host_format; /* formats host supports */
	21	uint16_t guest_format; /* format guest supplies */
	22	uint32_t size; /* size of vmcoreinfo region */
	23	uint64_t paddr; /* physical address of vmcoreinfo region */
	24	};
	25
	26	Only full write (of 16 bytes) are considered valid for further
	27	processing of entry values.
	28
	29	A write of 0 in guest_format will disable further processing of
	30	vmcoreinfo entry values & content.
	31
59fbfed9 MAL	32	You may write a guest_format that is not supported by the host, in
	33	which case the entry data can be ignored by qemu (but you may still
	34	access it through a debugger, via vmcoreinfo_realize::vmcoreinfo_state).
	35
6e43353f MAL	36	Format & content
	37	****************
	38
	39	As of qemu 2.11, only VMCOREINFO_FORMAT_ELF is supported.
	40
	41	The entry gives location and size of an ELF note that is appended in
	42	qemu dumps.
	43
	44	The note format/class must be of the target bitness and the size must
	45	be less than 1Mb.
d9feb517 MAL	46
	47	If the ELF note name is "VMCOREINFO", it is expected to be the Linux
	48	vmcoreinfo note (see Documentation/ABI/testing/sysfs-kernel-vmcoreinfo
	49	in Linux source). In this case, qemu dump code will read the content
	50	as a key=value text file, looking for "NUMBER(phys_base)" key
	51	value. The value is expected to be more accurate than architecture
	52	guess of the value. This is useful for KASLR-enabled guest with
	53	ancient tools not handling the VMCOREINFO note.