This document lists some variables that export to vmcoreinfo, and briefly describles what these variables indicate. It should be instructive for many people who do not know the vmcoreinfo. Suggested-by: Borislav Petkov <bp@xxxxxxx> Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx> --- Documentation/kdump/vmcoreinfo.txt | 500 +++++++++++++++++++++++++++++ 1 file changed, 500 insertions(+) create mode 100644 Documentation/kdump/vmcoreinfo.txt diff --git a/Documentation/kdump/vmcoreinfo.txt b/Documentation/kdump/vmcoreinfo.txt new file mode 100644 index 000000000000..8e444586b87b --- /dev/null +++ b/Documentation/kdump/vmcoreinfo.txt @@ -0,0 +1,500 @@ +================================================================ + VMCOREINFO +================================================================ + +======================= +What is the VMCOREINFO? +======================= + +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. + +PAGE_SIZE +--------- + +The size of a page. It is the smallest unit of data for memory +management in kernel. It is usually 4096 bytes and a page is aligned +on 4096 bytes. Used for computing page addresses. + +init_uts_ns +----------- + +This is the UTS namespace, which is used to isolate two specific +elements of the system that relate to the uname(2) system call. The UTS +namespace 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 node +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 can get the vmalloc start +value from this variable. This 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 can get 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 the contiguous memory. + +pglist_data +----------- + +The size of a pglist_data structure. This value will be 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 often 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 for 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 can compute their values based on the offset of these +variables. The variables are helpful to exclude 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 they are also helpful +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. +Each zone type is suitable for a different type of usage. + +User-space tools can 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 fields in this structure are simple, 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 indicate the vmalloc layer +information. Makedumpfile gets the start address of the vmalloc region. + +(zone.free_area, MAX_ORDER) +--------------------------- + +It indicates the maximum number of the array free_area. This macro is +used by the zone buddy allocator. User-space tools use this value to +iterate the free_area. + +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 +----------- + +Length of a log_buf. Used to read the number of strings from the +log_buf. + +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. + +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 string position. + +printk_log +---------- + +The size of a structure printk_log. Used to compute the size of +messages, and extract dmesg log. It can output human readable text. +Encapsulate 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 can +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 divided into +the array, it needs to know the number of the array when makedumpfile +computes 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_BUDDY_MAPCOUNT_VALUE(~PG_buddy) +|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline) +----------------------------------------------------------------- + +Page attributes. These flags are used to filter various unnecessary +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 +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 the +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 the 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 +-------- + +For AMD machine with SME feature, 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 (pgd/pud/pmd/pte) contains the memory encryption +mask and this is used to remove the SME mask to obtain the true physical +address. + +Currently, the sme_mask stores the value of sme_me_mask(bit 47). If need, +the bit(sme_mask) might be redefined in the future, but the bit 63 will +be reserved. + +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 more 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 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 in the crash kernel. + +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 address to physical +address. + +KERNELOFFSET +------------ + +The kernel randomization offset. Used to compute the page offset. If +KASLR is disabled, this value is zero. + +==== +arm +==== + +ARM_LPAE +-------- + +It indicates whether the crash kernel supports large physical address +extensions. Used to translate virtual address to physical address. + +==== +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. It can +get vmemmap list count and populate vmemmap regions info. If the vmemmap +address translation information is stored in the crash kernel, it helps +to translate vmemmap kernel virtual addresses. + +mmu_vmemmap_psize +----------------- + +The size of a page. Used to translate address 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 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 crash kernel enables SH extended mode. -- 2.17.1 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
