1 ================================================================
3 ================================================================
9 VMCOREINFO is a special ELF note section. It contains various
10 information from the kernel like structure size, page size, symbol
11 values, field offsets, etc. These data are packed into an ELF note
12 section and used by user-space tools like crash and makedumpfile to
13 analyze a kernel's memory layout.
19 init_uts_ns.name.release
20 ------------------------
22 The version of the Linux kernel. Used to find the corresponding source
23 code from which the kernel has been built. For example, crash uses it to
24 find the corresponding vmlinux in order to process vmcore.
29 The size of a page. It is the smallest unit of data used by the memory
30 management facilities. It is usually 4096 bytes of size and a page is
31 aligned on 4096 bytes. Used for computing page addresses.
36 The UTS namespace which is used to isolate two specific elements of the
37 system that relate to the uname(2) system call. It is named after the
38 data structure used to store information returned by the uname(2) system
41 User-space tools can get the kernel name, host name, kernel release
42 number, kernel version, architecture name and OS type from it.
47 An array node_states[N_ONLINE] which represents the set of online nodes
48 in a system, one bit position per node number. Used to keep track of
49 which nodes are in the system and online.
54 The global page directory pointer of the kernel. Used to translate
55 virtual to physical addresses.
60 Defines the beginning of the text section. In general, _stext indicates
61 the kernel start address. Used to convert a virtual address from the
62 direct kernel map to a physical address.
67 Stores the virtual area list. makedumpfile gets the vmalloc start value
68 from this variable and its value is necessary for vmalloc translation.
73 Physical addresses are translated to struct pages by treating them as
74 an index into the mem_map array. Right-shifting a physical address
75 PAGE_SHIFT bits converts it into a page frame number which is an index
76 into that mem_map array.
78 Used to map an address to the corresponding struct page.
83 Makedumpfile gets the pglist_data structure from this symbol, which is
84 used to describe the memory layout.
86 User-space tools use this to exclude free pages when dumping memory.
88 mem_section|(mem_section, NR_SECTION_ROOTS)|(mem_section, section_mem_map)
89 --------------------------------------------------------------------------
91 The address of the mem_section array, its length, structure size, and
92 the section_mem_map offset.
94 It exists in the sparse memory mapping model, and it is also somewhat
95 similar to the mem_map variable, both of them are used to translate an
101 The size of a page structure. struct page is an important data structure
102 and it is widely used to compute contiguous memory.
107 The size of a pglist_data structure. This value is used to check if the
108 pglist_data structure is valid. It is also used for checking the memory
114 The size of a zone structure. This value is used to check if the zone
115 structure has been found. It is also used for excluding free pages.
120 The size of a free_area structure. It indicates whether the free_area
121 structure is valid or not. Useful when excluding free pages.
126 The size of a list_head structure. Used when iterating lists in a
127 post-mortem analysis session.
132 The size of a nodemask_t type. Used to compute the number of online
135 (page, flags|_refcount|mapping|lru|_mapcount|private|compound_dtor|
136 compound_order|compound_head)
137 -------------------------------------------------------------------
139 User-space tools compute their values based on the offset of these
140 variables. The variables are used when excluding unnecessary pages.
142 (pglist_data, node_zones|nr_zones|node_mem_map|node_start_pfn|node_
143 spanned_pages|node_id)
144 -------------------------------------------------------------------
146 On NUMA machines, each NUMA node has a pg_data_t to describe its memory
147 layout. On UMA machines there is a single pglist_data which describes the
150 These values are used to check the memory type and to compute the
151 virtual address for memory map.
153 (zone, free_area|vm_stat|spanned_pages)
154 ---------------------------------------
156 Each node is divided into a number of blocks called zones which
157 represent ranges within memory. A zone is described by a structure zone.
159 User-space tools compute required values based on the offset of these
162 (free_area, free_list)
163 ----------------------
165 Offset of the free_list's member. This value is used to compute the number
168 Each zone has a free_area structure array called free_area[MAX_ORDER].
169 The free_list represents a linked list of free page blocks.
171 (list_head, next|prev)
172 ----------------------
174 Offsets of the list_head's members. list_head is used to define a
175 circular linked list. User-space tools need these in order to traverse
178 (vmap_area, va_start|list)
179 --------------------------
181 Offsets of the vmap_area's members. They carry vmalloc-specific
182 information. Makedumpfile gets the start address of the vmalloc region
185 (zone.free_area, MAX_ORDER)
186 ---------------------------
188 Free areas descriptor. User-space tools use this value to iterate the
189 free_area ranges. MAX_ORDER is used by the zone buddy allocator.
194 Index of the first record stored in the buffer log_buf. Used by
195 user-space tools to read the strings in the log_buf.
200 Console output is written to the ring buffer log_buf at index
201 log_first_idx. Used to get the kernel log.
211 The index that the next printk() record to read after the last clear
212 command. It indicates the first record after the last SYSLOG_ACTION
213 _CLEAR, like issued by 'dmesg -c'. Used by user-space tools to dump
219 The index of the next record to store in the buffer log_buf. Used to
220 compute the index of the current buffer position.
225 The size of a structure printk_log. Used to compute the size of
226 messages, and extract dmesg log. It encapsulates header information for
227 log_buf, such as timestamp, syslog level, etc.
229 (printk_log, ts_nsec|len|text_len|dict_len)
230 -------------------------------------------
232 It represents field offsets in struct printk_log. User space tools
233 parse it and check whether the values of printk_log's members have been
236 (free_area.free_list, MIGRATE_TYPES)
237 ------------------------------------
239 The number of migrate types for pages. The free_list is described by the
240 array. Used by tools to compute the number of free pages.
245 On linux-2.6.21 or later, the number of free pages is in
246 vm_stat[NR_FREE_PAGES]. Used to get the number of free pages.
248 PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision
249 |PG_head_mask|PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)
250 |PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)
251 -----------------------------------------------------------------
253 Page attributes. These flags are used to filter various unnecessary for
259 The HUGETLB_PAGE_DTOR flag denotes hugetlbfs pages. Makedumpfile
260 excludes these pages.
269 Used to convert the virtual address of an exported kernel symbol to its
270 corresponding physical address.
275 Used to walk through the whole page table and convert virtual addresses
276 to physical addresses. The init_top_pgt is somewhat similar to
277 swapper_pg_dir, but it is only used in x86_64.
282 User-space tools need to know whether the crash kernel was in 5-level
288 This is a struct pglist_data array and stores all NUMA nodes
289 information. Makedumpfile gets the pglist_data structure from it.
291 (node_data, MAX_NUMNODES)
292 -------------------------
294 The maximum number of nodes in system.
299 The kernel randomization offset. Used to compute the page offset. If
300 KASLR is disabled, this value is zero.
305 Currently unused by Makedumpfile. Used to compute the module virtual
311 AMD-specific with SME support: it indicates the secure memory encryption
312 mask. Makedumpfile tools need to know whether the crash kernel was
313 encrypted. If SME is enabled in the first kernel, the crash kernel's
314 page table entries (pgd/pud/pmd/pte) contain the memory encryption
315 mask. This is used to remove the SME mask and obtain the true physical
318 Currently, sme_mask stores the value of the C-bit position. If needed,
319 additional SME-relevant info can be placed in that variable.
322 [ misc ][ enc bit ][ other misc SME info ]
323 0000_0000_0000_0000_1000_0000_0000_0000_0000_0000_..._0000
324 63 59 55 51 47 43 39 35 31 27 ... 3
333 Denotes whether physical address extensions are enabled. It has the cost
334 of a higher page table lookup overhead, and also consumes more page
335 table space per process. Used to check whether PAE was enabled in the
336 crash kernel when converting virtual addresses to physical addresses.
342 pgdat_list|(pgdat_list, MAX_NUMNODES)
343 -------------------------------------
345 pg_data_t array storing all NUMA nodes information. MAX_NUMNODES
346 indicates the number of the nodes.
348 node_memblk|(node_memblk, NR_NODE_MEMBLKS)
349 ------------------------------------------
351 List of node memory chunks. Filled when parsing the SRAT table to obtain
352 information about memory nodes. NR_NODE_MEMBLKS indicates the number of
355 These values are used to compute the number of nodes the crashed kernel used.
357 node_memblk_s|(node_memblk_s, start_paddr)|(node_memblk_s, size)
358 ----------------------------------------------------------------
360 The size of a struct node_memblk_s and the offsets of the
361 node_memblk_s's members. Used to compute the number of nodes.
366 User-space tools need to know whether the crash kernel was in 3-level or
367 4-level paging mode. Used to distinguish the page table.
376 The maximum number of bits for virtual addresses. Used to compute the
377 virtual memory ranges.
382 The offset between the kernel virtual and physical mappings. Used to
383 translate virtual to physical addresses.
388 Indicates the physical address of the start of memory. Similar to
389 kimage_voffset, which is used to translate virtual to physical
395 The kernel randomization offset. Used to compute the page offset. If
396 KASLR is disabled, this value is zero.
405 It indicates whether the crash kernel supports large physical address
406 extensions. Used to translate virtual to physical addresses.
415 An array with a pointer to the lowcore of every CPU. Used to print the
416 psw and all registers information.
421 Used to get the vmalloc_start address from the high_memory symbol.
423 (lowcore_ptr, NR_CPUS)
424 ----------------------
426 The maximum number of CPUs.
433 node_data|(node_data, MAX_NUMNODES)
434 -----------------------------------
446 The vmemmap_list maintains the entire vmemmap physical mapping. Used
447 to get vmemmap list count and populated vmemmap regions info. If the
448 vmemmap address translation information is stored in the crash kernel,
449 it is used to translate vmemmap kernel virtual addresses.
454 The size of a page. Used to translate virtual to physical addresses.
459 Page size definitions, i.e. 4k, 64k, or 16M.
461 Used to make vtop translations.
463 vmemmap_backing|(vmemmap_backing, list)|(vmemmap_backing, phys)|
464 (vmemmap_backing, virt_addr)
465 ----------------------------------------------------------------
467 The vmemmap virtual address space management does not have a traditional
468 page table to track which virtual struct pages are backed by a physical
469 mapping. The virtual to physical mappings are tracked in a simple linked
472 User-space tools need to know the offset of list, phys and virt_addr
473 when computing the count of vmemmap regions.
475 mmu_psize_def|(mmu_psize_def, shift)
476 ------------------------------------
478 The size of a struct mmu_psize_def and the offset of mmu_psize_def's
481 Used in vtop translations.
487 node_data|(node_data, MAX_NUMNODES)
488 -----------------------------------
495 Indicates whether the crashed kernel enabled SH extended mode.