/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 library
400000 12845d 0 1 0 1 /bin/bash
401000 12845e 0 1 0 1 /bin/bash
402000 12845f 0 1 0 1 /bin/bash
This tells us for example that the virtual address 0x400000 maps to the physical address
0x12845d000.
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.sowhich gives us:
7f8af99f8000-7f8af99ff000: a virtual address range that belong to the process, possibly containing multiple pages./lib/libuClibc-1.0.22.sothe name of the library that owns that memory.
loop over each page of each address range, and ask
/proc/<pid>/pagemapfor more information about that page, including the physical address.
pagemap_dump.c
#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