/proc/[pid]/pagemaps and /proc/[pid]/maps | linux
F**/proc/<pid>/pagemap
+ /proc/<pid>/maps
dump example program**
Here is a pagemap
example that converts virtual addresses to physical: Is there any API for determining the physical address from virtual address in Linux?
The following program uses both /proc/<pid>/pagemap
+ /proc/<pid>/maps
to dump page table information to show how they can be used together. Usage:
sudo ./pagemap_dump.out <pid>
Sample output:
addr pfn soft-dirty file/shared swapped present library400000 12845d 0 1 0 1 /bin/bash401000 12845e 0 1 0 1 /bin/bash402000 12845f 0 1 0 1 /bin/bash
This tells us for example that the virtual address 0x400000
maps to the physical address0x12845d000
.
Why sudo
is required: https://unix.stackexchange.com/questions/345915/how-to-change-permission-of-proc-self-pagemap-file/383838#383838
This program works in two steps:
parse the human readable lines lines from
/proc/<pid>/maps
. This files contains lines of form:7ffff7b6d000-7ffff7bdd000 r-xp 00000000 fe:00 658 /lib/libuClibc-1.0.22.so
which gives us:
7f8af99f8000-7f8af99ff000
: a virtual address range that belong to the process, possibly containing multiple pages./lib/libuClibc-1.0.22.so
the name of the library that owns that memory.
loop over each page of each address range, and ask
/proc/<pid>/pagemap
for more information about that page, including the physical address.
#define _XOPEN_SOURCE 700#include <errno.h>#include <fcntl.h>#include <stdint.h>#include <stdio.h>#include <stdlib.h>#include <sys/types.h>#include <unistd.h>typedef struct { uint64_t pfn : 55; unsigned int soft_dirty : 1; unsigned int file_page : 1; unsigned int swapped : 1; unsigned int present : 1;} PagemapEntry;/* Parse the pagemap entry for the given virtual address. * * @param[out] entry the parsed entry * @param[in] pagemap_fd file descriptor to an open /proc/pid/pagemap file * @param[in] vaddr virtual address to get entry for * @return 0 for success, 1 for failure */int pagemap_get_entry(PagemapEntry *entry, int pagemap_fd, uintptr_t vaddr){ size_t nread; ssize_t ret; uint64_t data; nread = 0; while (nread < sizeof(data)) { ret = pread(pagemap_fd, ((uint8_t*)&data) + nread, sizeof(data) - nread, (vaddr / sysconf(_SC_PAGE_SIZE)) * sizeof(data) + nread); nread += ret; if (ret <= 0) { return 1; } } entry->pfn = data & (((uint64_t)1 << 55) - 1); entry->soft_dirty = (data >> 55) & 1; entry->file_page = (data >> 61) & 1; entry->swapped = (data >> 62) & 1; entry->present = (data >> 63) & 1; return 0;}/* Convert the given virtual address to physical using /proc/PID/pagemap. * * @param[out] paddr physical address * @param[in] pid process to convert for * @param[in] vaddr virtual address to get entry for * @return 0 for success, 1 for failure */int virt_to_phys_user(uintptr_t *paddr, pid_t pid, uintptr_t vaddr){ char pagemap_file[BUFSIZ]; int pagemap_fd; snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)pid); pagemap_fd = open(pagemap_file, O_RDONLY); if (pagemap_fd < 0) { return 1; } PagemapEntry entry; if (pagemap_get_entry(&entry, pagemap_fd, vaddr)) { return 1; } close(pagemap_fd); *paddr = (entry.pfn * sysconf(_SC_PAGE_SIZE)) + (vaddr % sysconf(_SC_PAGE_SIZE)); return 0;}int main(int argc, char **argv){ char buffer[BUFSIZ]; char maps_file[BUFSIZ]; char pagemap_file[BUFSIZ]; int maps_fd; int offset = 0; int pagemap_fd; pid_t pid; if (argc < 2) { printf("Usage: %s pid\n", argv[0]); return EXIT_FAILURE; } pid = strtoull(argv[1], NULL, 0); snprintf(maps_file, sizeof(maps_file), "/proc/%ju/maps", (uintmax_t)pid); snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)pid); maps_fd = open(maps_file, O_RDONLY); if (maps_fd < 0) { perror("open maps"); return EXIT_FAILURE; } pagemap_fd = open(pagemap_file, O_RDONLY); if (pagemap_fd < 0) { perror("open pagemap"); return EXIT_FAILURE; } printf("addr pfn soft-dirty file/shared swapped present library\n"); for (;;) { ssize_t length = read(maps_fd, buffer + offset, sizeof buffer - offset); if (length <= 0) break; length += offset; for (size_t i = offset; i < (size_t)length; i++) { uintptr_t low = 0, high = 0; if (buffer[i] == '\n' && i) { const char *lib_name; size_t y; /* Parse a line from maps. Each line contains a range that contains many pages. */ { size_t x = i - 1; while (x && buffer[x] != '\n') x--; if (buffer[x] == '\n') x++; while (buffer[x] != '-' && x < sizeof buffer) { char c = buffer[x++]; low *= 16; if (c >= '0' && c <= '9') { low += c - '0'; } else if (c >= 'a' && c <= 'f') { low += c - 'a' + 10; } else { break; } } while (buffer[x] != '-' && x < sizeof buffer) x++; if (buffer[x] == '-') x++; while (buffer[x] != ' ' && x < sizeof buffer) { char c = buffer[x++]; high *= 16; if (c >= '0' && c <= '9') { high += c - '0'; } else if (c >= 'a' && c <= 'f') { high += c - 'a' + 10; } else { break; } } lib_name = 0; for (int field = 0; field < 4; field++) { x++; while(buffer[x] != ' ' && x < sizeof buffer) x++; } while (buffer[x] == ' ' && x < sizeof buffer) x++; y = x; while (buffer[y] != '\n' && y < sizeof buffer) y++; buffer[y] = 0; lib_name = buffer + x; } /* Get info about all pages in this page range with pagemap. */ { PagemapEntry entry; for (uintptr_t addr = low; addr < high; addr += sysconf(_SC_PAGE_SIZE)) { /* TODO always fails for the last page (vsyscall), why? pread returns 0. */ if (!pagemap_get_entry(&entry, pagemap_fd, addr)) { printf("%jx %jx %u %u %u %u %s\n", (uintmax_t)addr, (uintmax_t)entry.pfn, entry.soft_dirty, entry.file_page, entry.swapped, entry.present, lib_name ); } } } buffer[y] = '\n'; } } } close(maps_fd); close(pagemap_fd); return EXIT_SUCCESS;}
Oooh K, the index was correct but comparing off64_t o (8bytes) with long index was interpreting o wrong hence why I was getting that error.Ha! this was a stupid mistake.So adding the appropriate header took care of that.
Missing header :-/ sigh fixes the issue of comparing off64_t with a unsigned long.
Use page-types.c as a guide to what you are looking for, it parses the contents of both pagemap and maps:https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/plain/Documentation/vm/page-types.c?h=linux-2.6.32.y