PMAP(1)

PMAP(1) | NetBSD General Commands Manual | PMAP(1)

# NAME

pmap — display process memory map

# SYNOPSIS

pmap | [-adlmPRsv] [-A address] [-D number] [-E address] [-M core] [-N system] [-p pid] [-S address] [-V address] [pid ...]

# DESCRIPTION

The pmap utility lists the virtual memory mappings underlying the given process. The start address of each entry is always given, and, depending on the options given, other information such as the end address, the underlying file's device and inode numbers, and various protection information will be displayed, along with the path to the file, if such data is available.

By default, pmap displays information for its parent process, so that when run from a shell prompt, the shell's memory information is displayed. If other PIDs are given as arguments on the command line, information for those processes will be printed also. If the special PID of 0 is given, then information for the kernel's memory map is printed.

The options are as follows:

-A address
  Dumps the vm_amap structure found at address.
-a
  Display “all” information from the process's memory map. This output mode is an amalgam of the contents of the Solaris, Linux, and NetBSD style output modes.
-D number
  Enable various debug facilities. The number is a bit mask of the values:

  0x01
    dump the process's vmspace structure
  0x02
    dump the process's vm_map structure
  0x04
    dump the vm_map.header structure
  0x08
    dump each vm_map_entry in its entirety
  0x10
    dump the vm_amap structure attached to the vm_map_entry, if applicable
  0x20
    dump the vm_amap slot data, if present (requires 0x10)
  0x40
    dump the vm_anon data from the am_anon array, if present (requires 0x20)
  0x1000
    dump the namei cache as it is traversed
-d
  Dumps the vm_map and vm_map_entry structures in a style similar to that of ddb(4). When combined with the -v option, the device number, inode number, name, vnode addresses, or other identifying information from the vm_map_entries will be printed.
-E address
  Dumps the vm_map_entry structure found at address.
-l
  Dumps information in a format like the contents of the maps pseudo-file under the /proc file system which was, in turn, modeled after the similarly named entry in the Linux /proc file system. When combined with the -v option, identifiers for all entries are printed.
-M core
  Extract values associated with the name list from the specified core instead of the default /dev/kmem.
-m
  Dumps information in the same format as the map pseudo-file of the /proc file system. When the -v option is also given, device number, inode number, and filename or other identifying information is printed.
-N system
  Extract the name list from the specified system instead of the default /netbsd.
-P
  Causes pmap to print information about itself.
-p pid
  Tells pmap to print information about the given process. If -p pid occurs last on the command line, the -p is optional.
-R
  Recurse into submaps. In some cases, a vm_map_entry in the kernel will point to a submap. Using this flag tells pmap to print the entries of the submap as well. The submap output is indented, and does not affect any total printed at the bottom of the output.
-S address
  Dumps the vmspace structure found at address.
-s
  The Solaris style output format, modeled after the Solaris command of the same name. This is the default output style.
-V address
  Dumps the vm_map structure found at address. Note that if you print the vm_map of a process, there may not be a way to properly determine which map entries are related to the stack.
-v
  Verbose output. When used with -d, -l, or -m, more information is printed, possibly including device and inode numbers, file path names, or other identifying information. If specified more than once, a small note will be printed in between two entries that are not adjacent, making the visual identification of spaces in the process's map easier to see, that indicates the number of pages and the amount of memory space that is skipped.

The -P and -p options override each other, so the last one to appear on the command line takes effect. If you do wish to see information about pmap and another process as the same time, simply omit the -p and place the extra PID at the end of the command line.

# EXIT STATUS

pmap exits 0 on success, and >0 if an error occurred.

# EXAMPLES

While the meaning of most of the output is self-evident, some pieces of it may appear to be a little inscrutable.

Here is a portion of the default output from pmap being run at an sh(1) prompt showing the starting address of the map entry, the size of the map entry, the current protection level of the map entry, and either the name of the file backing the entry or some other descriptive text.

    $ pmap
    08048000    420K read/exec         /bin/sh
    080B1000      8K read/write        /bin/sh
    080B3000     28K read/write          [ anon ]
    080BA000     16K read/write/exec     [ heap ]
    ...

When the ddb(4) output style is selected, the first thing printed is the contents of the vm_map structure, followed by the individual map entries.

    $ pmap -d
    MAP 0xcf7cac84: [0x0->0xbfbfe000]
            #ent=8, sz=34041856, ref=1, version=20, flags=0x41
            pmap=0xcf44cee0(resident=<unknown>)
     - 0xcfa3a358: 0x8048000->0x80b1000: obj=0xcf45a8e8/0x0, amap=0x0/0
            submap=F, cow=T, nc=T, prot(max)=5/7, inh=1, wc=0, adv=0
    ...

The value of the flags field (in hexadecimal) is taken from the include file <uvm/uvm_map.h>:

VM_MAP_PAGEABLE | 0x01 entries are pageable
VM_MAP_INTRSAFE | 0x02 interrupt safe map
VM_MAP_WIREFUTURE | 0x04 future mappings are wired
VM_MAP_BUSY | 0x08 map is busy
VM_MAP_WANTLOCK | 0x10 want to write-lock
VM_MAP_DYING | 0x20 map is being destroyed
VM_MAP_TOPDOWN | 0x40 arrange map top-down

The “submap”, “cow”, and “nc” fields are true or false, and indicate whether the map is a submap, whether it is marked for copy on write, and whether it needs a copy. The “prot” (or protection) field, along with “max” (maximum protection allowed) are made up of the following flags from <uvm/uvm_extern.h>:

UVM_PROT_READ | 0x01 read allowed
UVM_PROT_WRITE | 0x02 write allowed
UVM_PROT_EXEC | 0x04 execute allowed

The “obj” and “amap” fields are pointers to, and offsets into, the underlying uvm_object or amap. The value for resident is always unknown because digging such information out of the kernel is beyond the scope of this application.

The two output styles that mirror the contents of the /proc file system appear as follows:

    $ pmap -m
    0x8048000 0x80b1000 r-x rwx COW NC 1 0 0
    0x80b1000 0x80b3000 rw- rwx COW NC 1 0 0
    0x80b3000 0x80ba000 rw- rwx COW NNC 1 0 0
    0x80ba000 0x80be000 rwx rwx COW NNC 1 0 0
    ...

    $ pmap -l
    08048000-080b1000 r-xp 00000000 00:00 70173     /bin/sh
    080b1000-080b3000 rw-p 00068000 00:00 70173     /bin/sh
    080b3000-080ba000 rw-p 00000000 00:00 0
    080ba000-080be000 rwxp 00000000 00:00 0
    ...

Here the protection and maximum protection values are indicated with ‘r', ‘w', and ‘x' characters, indicating read permission, write permission, and execute permission, respectively. The “COW”, “NC”, and “NNC” values that follow indicate, again, that the map is marked for copy on write and either needs or does not need a copy. It is also possible to see the value “NCOW” here, which indicates that an entry will not be copied. The three following numbers indicate the inheritance type of the map, the wired count of the map, and any advice value assigned via madvise(2).

In the second form, the permissions indicated are followed by a ‘p' or ‘s' character indicating whether the map entry is private or shared (copy on write or not), and the numbers are the offset into the underlying object, the device and numbers of the object if it is a file, and the path to the file (if available).

As noted above (see section DESCRIPTION), the “all” output format is an amalgam of the previous output formats.

    $ pmap -a
    Start    End         Size  Offset   rwxpc  RWX  I/W/A ...
    08048000-080b0fff     420k 00000000 r-xp+ (rwx) 1/0/0 ...
    ...

In this format, the column labeled “rwxpc” contains the permissions for the mapping along with the shared/private flag, and a character indicating whether the mapping needs to be copied on write (‘+') or has already been copied (‘-') and is followed by a column that indicates the maximum permissions for the map entry. The column labeled “I/W/A” indicates the inheritance, wired, and advice values for the map entry, as previously described. The pointer value at the end of the output line for entries backed by vnodes is the address of the vnode in question.

# SEE ALSO

ls(1), stat(1), madvise(2), mmap(2), kvm(3), ddb(4), mount_procfs(8), pmap(9)

# HISTORY

The pmap utility appeared in NetBSD 2.0.

# AUTHORS

The pmap utility and documentation was written by Andrew Brown <atatat@NetBSD.org>.

# BUGS

Very little will work unless pmap is reading from the correct kernel in order to retrieve the proper symbol information.

Since processes can change state while pmap is running, some of the information printed may be inaccurate. This is especially important to consider when examining the kernel's map, since merely executing pmap will cause some of the information to change.

The pathnames to files backing certain vnodes (such as the text and data sections of programs and shared libraries) are extracted from the kernel's namei cache which is considerably volatile. If a path is not found there in its entirety, as much information as was available will be printed. In most cases, simply running ls(1) or stat(1) with the expected path to the file will cause the information to be reentered into the cache.

The Solaris command by the same name has some interesting command line flags that would be nice to emulate here. In particular, the -r option that lists a process's reserved addresses, and the -x option that prints resident/shared/private mapping details for each entry.

Some of the output modes can be or are wider than the standard 80 columns of a terminal. Some sort of formatting might be nice.

# SECURITY CONSIDERATIONS

The Solaris command controls access to processes the user does not own via the permissions of its /proc file system. Since pmap uses kvm(3) to read the requested data directly from kernel memory, no such limitation exists.

If any of the -A, -E, -M, -N, -S, or -V options are used, any extra privileges that pmap has will be dropped.

February 6, 2009 | NetBSD 5.99