| ========== |
| VMCOREINFO |
| ========== |
| |
| What is it? |
| =========== |
| |
| VMCOREINFO is a special ELF note section. It contains various |
| information from the kernel like structure size, page size, symbol |
| values, field offsets, etc. These data are packed into an ELF note |
| section and used by user-space tools like crash and makedumpfile to |
| analyze a kernel's memory layout. |
| |
| Common variables |
| ================ |
| |
| init_uts_ns.name.release |
| ------------------------ |
| |
| The version of the Linux kernel. Used to find the corresponding source |
| code from which the kernel has been built. For example, crash uses it to |
| find the corresponding vmlinux in order to process vmcore. |
| |
| PAGE_SIZE |
| --------- |
| |
| The size of a page. It is the smallest unit of data used by the memory |
| management facilities. It is usually 4096 bytes of size and a page is |
| aligned on 4096 bytes. Used for computing page addresses. |
| |
| init_uts_ns |
| ----------- |
| |
| The UTS namespace which is used to isolate two specific elements of the |
| system that relate to the uname(2) system call. It is named after the |
| data structure used to store information returned by the uname(2) system |
| call. |
| |
| User-space tools can get the kernel name, host name, kernel release |
| number, kernel version, architecture name and OS type from it. |
| |
| node_online_map |
| --------------- |
| |
| An array node_states[N_ONLINE] which represents the set of online nodes |
| in a system, one bit position per node number. Used to keep track of |
| which nodes are in the system and online. |
| |
| swapper_pg_dir |
| -------------- |
| |
| The global page directory pointer of the kernel. Used to translate |
| virtual to physical addresses. |
| |
| _stext |
| ------ |
| |
| Defines the beginning of the text section. In general, _stext indicates |
| the kernel start address. Used to convert a virtual address from the |
| direct kernel map to a physical address. |
| |
| vmap_area_list |
| -------------- |
| |
| Stores the virtual area list. makedumpfile gets the vmalloc start value |
| from this variable and its value is necessary for vmalloc translation. |
| |
| mem_map |
| ------- |
| |
| Physical addresses are translated to struct pages by treating them as |
| an index into the mem_map array. Right-shifting a physical address |
| PAGE_SHIFT bits converts it into a page frame number which is an index |
| into that mem_map array. |
| |
| Used to map an address to the corresponding struct page. |
| |
| contig_page_data |
| ---------------- |
| |
| Makedumpfile gets the pglist_data structure from this symbol, which is |
| used to describe the memory layout. |
| |
| User-space tools use this to exclude free pages when dumping memory. |
| |
| mem_section|(mem_section, NR_SECTION_ROOTS)|(mem_section, section_mem_map) |
| -------------------------------------------------------------------------- |
| |
| The address of the mem_section array, its length, structure size, and |
| the section_mem_map offset. |
| |
| It exists in the sparse memory mapping model, and it is also somewhat |
| similar to the mem_map variable, both of them are used to translate an |
| address. |
| |
| page |
| ---- |
| |
| The size of a page structure. struct page is an important data structure |
| and it is widely used to compute contiguous memory. |
| |
| pglist_data |
| ----------- |
| |
| The size of a pglist_data structure. This value is used to check if the |
| pglist_data structure is valid. It is also used for checking the memory |
| type. |
| |
| zone |
| ---- |
| |
| The size of a zone structure. This value is used to check if the zone |
| structure has been found. It is also used for excluding free pages. |
| |
| free_area |
| --------- |
| |
| The size of a free_area structure. It indicates whether the free_area |
| structure is valid or not. Useful when excluding free pages. |
| |
| list_head |
| --------- |
| |
| The size of a list_head structure. Used when iterating lists in a |
| post-mortem analysis session. |
| |
| nodemask_t |
| ---------- |
| |
| The size of a nodemask_t type. Used to compute the number of online |
| nodes. |
| |
| (page, flags|_refcount|mapping|lru|_mapcount|private|compound_dtor|compound_order|compound_head) |
| ------------------------------------------------------------------------------------------------- |
| |
| User-space tools compute their values based on the offset of these |
| variables. The variables are used when excluding unnecessary pages. |
| |
| (pglist_data, node_zones|nr_zones|node_mem_map|node_start_pfn|node_spanned_pages|node_id) |
| ----------------------------------------------------------------------------------------- |
| |
| On NUMA machines, each NUMA node has a pg_data_t to describe its memory |
| layout. On UMA machines there is a single pglist_data which describes the |
| whole memory. |
| |
| These values are used to check the memory type and to compute the |
| virtual address for memory map. |
| |
| (zone, free_area|vm_stat|spanned_pages) |
| --------------------------------------- |
| |
| Each node is divided into a number of blocks called zones which |
| represent ranges within memory. A zone is described by a structure zone. |
| |
| User-space tools compute required values based on the offset of these |
| variables. |
| |
| (free_area, free_list) |
| ---------------------- |
| |
| Offset of the free_list's member. This value is used to compute the number |
| of free pages. |
| |
| Each zone has a free_area structure array called free_area[MAX_ORDER]. |
| The free_list represents a linked list of free page blocks. |
| |
| (list_head, next|prev) |
| ---------------------- |
| |
| Offsets of the list_head's members. list_head is used to define a |
| circular linked list. User-space tools need these in order to traverse |
| lists. |
| |
| (vmap_area, va_start|list) |
| -------------------------- |
| |
| Offsets of the vmap_area's members. They carry vmalloc-specific |
| information. Makedumpfile gets the start address of the vmalloc region |
| from this. |
| |
| (zone.free_area, MAX_ORDER) |
| --------------------------- |
| |
| Free areas descriptor. User-space tools use this value to iterate the |
| free_area ranges. MAX_ORDER is used by the zone buddy allocator. |
| |
| log_first_idx |
| ------------- |
| |
| Index of the first record stored in the buffer log_buf. Used by |
| user-space tools to read the strings in the log_buf. |
| |
| log_buf |
| ------- |
| |
| Console output is written to the ring buffer log_buf at index |
| log_first_idx. Used to get the kernel log. |
| |
| log_buf_len |
| ----------- |
| |
| log_buf's length. |
| |
| clear_idx |
| --------- |
| |
| The index that the next printk() record to read after the last clear |
| command. It indicates the first record after the last SYSLOG_ACTION |
| _CLEAR, like issued by 'dmesg -c'. Used by user-space tools to dump |
| the dmesg log. |
| |
| log_next_idx |
| ------------ |
| |
| The index of the next record to store in the buffer log_buf. Used to |
| compute the index of the current buffer position. |
| |
| printk_log |
| ---------- |
| |
| The size of a structure printk_log. Used to compute the size of |
| messages, and extract dmesg log. It encapsulates header information for |
| log_buf, such as timestamp, syslog level, etc. |
| |
| (printk_log, ts_nsec|len|text_len|dict_len) |
| ------------------------------------------- |
| |
| It represents field offsets in struct printk_log. User space tools |
| parse it and check whether the values of printk_log's members have been |
| changed. |
| |
| (free_area.free_list, MIGRATE_TYPES) |
| ------------------------------------ |
| |
| The number of migrate types for pages. The free_list is described by the |
| array. Used by tools to compute the number of free pages. |
| |
| NR_FREE_PAGES |
| ------------- |
| |
| On linux-2.6.21 or later, the number of free pages is in |
| vm_stat[NR_FREE_PAGES]. Used to get the number of free pages. |
| |
| PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision|PG_head_mask |
| ------------------------------------------------------------------------------ |
| |
| Page attributes. These flags are used to filter various unnecessary for |
| dumping pages. |
| |
| PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline) |
| ----------------------------------------------------------------------------- |
| |
| More page attributes. These flags are used to filter various unnecessary for |
| dumping pages. |
| |
| |
| HUGETLB_PAGE_DTOR |
| ----------------- |
| |
| The HUGETLB_PAGE_DTOR flag denotes hugetlbfs pages. Makedumpfile |
| excludes these pages. |
| |
| x86_64 |
| ====== |
| |
| phys_base |
| --------- |
| |
| Used to convert the virtual address of an exported kernel symbol to its |
| corresponding physical address. |
| |
| init_top_pgt |
| ------------ |
| |
| Used to walk through the whole page table and convert virtual addresses |
| to physical addresses. The init_top_pgt is somewhat similar to |
| swapper_pg_dir, but it is only used in x86_64. |
| |
| pgtable_l5_enabled |
| ------------------ |
| |
| User-space tools need to know whether the crash kernel was in 5-level |
| paging mode. |
| |
| node_data |
| --------- |
| |
| This is a struct pglist_data array and stores all NUMA nodes |
| information. Makedumpfile gets the pglist_data structure from it. |
| |
| (node_data, MAX_NUMNODES) |
| ------------------------- |
| |
| The maximum number of nodes in system. |
| |
| KERNELOFFSET |
| ------------ |
| |
| The kernel randomization offset. Used to compute the page offset. If |
| KASLR is disabled, this value is zero. |
| |
| KERNEL_IMAGE_SIZE |
| ----------------- |
| |
| Currently unused by Makedumpfile. Used to compute the module virtual |
| address by Crash. |
| |
| sme_mask |
| -------- |
| |
| AMD-specific with SME support: it indicates the secure memory encryption |
| mask. Makedumpfile tools need to know whether the crash kernel was |
| encrypted. If SME is enabled in the first kernel, the crash kernel's |
| page table entries (pgd/pud/pmd/pte) contain the memory encryption |
| mask. This is used to remove the SME mask and obtain the true physical |
| address. |
| |
| Currently, sme_mask stores the value of the C-bit position. If needed, |
| additional SME-relevant info can be placed in that variable. |
| |
| For example:: |
| |
| [ misc ][ enc bit ][ other misc SME info ] |
| 0000_0000_0000_0000_1000_0000_0000_0000_0000_0000_..._0000 |
| 63 59 55 51 47 43 39 35 31 27 ... 3 |
| |
| x86_32 |
| ====== |
| |
| X86_PAE |
| ------- |
| |
| Denotes whether physical address extensions are enabled. It has the cost |
| of a higher page table lookup overhead, and also consumes more page |
| table space per process. Used to check whether PAE was enabled in the |
| crash kernel when converting virtual addresses to physical addresses. |
| |
| ia64 |
| ==== |
| |
| pgdat_list|(pgdat_list, MAX_NUMNODES) |
| ------------------------------------- |
| |
| pg_data_t array storing all NUMA nodes information. MAX_NUMNODES |
| indicates the number of the nodes. |
| |
| node_memblk|(node_memblk, NR_NODE_MEMBLKS) |
| ------------------------------------------ |
| |
| List of node memory chunks. Filled when parsing the SRAT table to obtain |
| information about memory nodes. NR_NODE_MEMBLKS indicates the number of |
| node memory chunks. |
| |
| These values are used to compute the number of nodes the crashed kernel used. |
| |
| node_memblk_s|(node_memblk_s, start_paddr)|(node_memblk_s, size) |
| ---------------------------------------------------------------- |
| |
| The size of a struct node_memblk_s and the offsets of the |
| node_memblk_s's members. Used to compute the number of nodes. |
| |
| PGTABLE_3|PGTABLE_4 |
| ------------------- |
| |
| User-space tools need to know whether the crash kernel was in 3-level or |
| 4-level paging mode. Used to distinguish the page table. |
| |
| ARM64 |
| ===== |
| |
| VA_BITS |
| ------- |
| |
| The maximum number of bits for virtual addresses. Used to compute the |
| virtual memory ranges. |
| |
| kimage_voffset |
| -------------- |
| |
| The offset between the kernel virtual and physical mappings. Used to |
| translate virtual to physical addresses. |
| |
| PHYS_OFFSET |
| ----------- |
| |
| Indicates the physical address of the start of memory. Similar to |
| kimage_voffset, which is used to translate virtual to physical |
| addresses. |
| |
| KERNELOFFSET |
| ------------ |
| |
| The kernel randomization offset. Used to compute the page offset. If |
| KASLR is disabled, this value is zero. |
| |
| KERNELPACMASK |
| ------------- |
| |
| The mask to extract the Pointer Authentication Code from a kernel virtual |
| address. |
| |
| arm |
| === |
| |
| ARM_LPAE |
| -------- |
| |
| It indicates whether the crash kernel supports large physical address |
| extensions. Used to translate virtual to physical addresses. |
| |
| s390 |
| ==== |
| |
| lowcore_ptr |
| ----------- |
| |
| An array with a pointer to the lowcore of every CPU. Used to print the |
| psw and all registers information. |
| |
| high_memory |
| ----------- |
| |
| Used to get the vmalloc_start address from the high_memory symbol. |
| |
| (lowcore_ptr, NR_CPUS) |
| ---------------------- |
| |
| The maximum number of CPUs. |
| |
| powerpc |
| ======= |
| |
| |
| node_data|(node_data, MAX_NUMNODES) |
| ----------------------------------- |
| |
| See above. |
| |
| contig_page_data |
| ---------------- |
| |
| See above. |
| |
| vmemmap_list |
| ------------ |
| |
| The vmemmap_list maintains the entire vmemmap physical mapping. Used |
| to get vmemmap list count and populated vmemmap regions info. If the |
| vmemmap address translation information is stored in the crash kernel, |
| it is used to translate vmemmap kernel virtual addresses. |
| |
| mmu_vmemmap_psize |
| ----------------- |
| |
| The size of a page. Used to translate virtual to physical addresses. |
| |
| mmu_psize_defs |
| -------------- |
| |
| Page size definitions, i.e. 4k, 64k, or 16M. |
| |
| Used to make vtop translations. |
| |
| vmemmap_backing|(vmemmap_backing, list)|(vmemmap_backing, phys)|(vmemmap_backing, virt_addr) |
| -------------------------------------------------------------------------------------------- |
| |
| The vmemmap virtual address space management does not have a traditional |
| page table to track which virtual struct pages are backed by a physical |
| mapping. The virtual to physical mappings are tracked in a simple linked |
| list format. |
| |
| User-space tools need to know the offset of list, phys and virt_addr |
| when computing the count of vmemmap regions. |
| |
| mmu_psize_def|(mmu_psize_def, shift) |
| ------------------------------------ |
| |
| The size of a struct mmu_psize_def and the offset of mmu_psize_def's |
| member. |
| |
| Used in vtop translations. |
| |
| sh |
| == |
| |
| node_data|(node_data, MAX_NUMNODES) |
| ----------------------------------- |
| |
| See above. |
| |
| X2TLB |
| ----- |
| |
| Indicates whether the crashed kernel enabled SH extended mode. |