[PLUG] pmap Output Help Needed

[Casey Bralla <MailList@NerdWorld.org>]

I'm writing an application that examines the memory used by running programs.  
I'm trying to disect the output of pmap, but I'm a little confused and hope 
somebody can help.

My version of pmap is fairly basic, only allowing the "-x", "-d", & "-q" 
parameters, which gives info such as this:

 pmap -d 25849
25849:   /bin/bash
Address           Kbytes Mode  Offset           Device    Mapping
0000000000400000     740 r-x-- 0000000000000000 003:00001 bash
00000000006b8000       4 r---- 00000000000b8000 003:00001 bash
00000000006b9000      40 rw--- 00000000000b9000 003:00001 bash
00000000006c3000     384 rw--- 00000000006c3000 000:00000   [ anon ]
00007f0b57c27000      44 r-x-- 0000000000000000 003:00001 libnss_files-2.9.so
00007f0b57c32000    2044 ----- 000000000000b000 003:00001 libnss_files-2.9.so
00007f0b57e31000       4 r---- 000000000000a000 003:00001 libnss_files-2.9.so
00007f0b57e32000       4 rw--- 000000000000b000 003:00001 libnss_files-2.9.so
00007f0b57e33000      40 r-x-- 0000000000000000 003:00001 libnss_nis-2.9.so
00007f0b57e3d000    2044 ----- 000000000000a000 003:00001 libnss_nis-2.9.so
00007f0b5803c000       4 r---- 0000000000009000 003:00001 libnss_nis-2.9.so
00007f0b5803d000       4 rw--- 000000000000a000 003:00001 libnss_nis-2.9.so
00007f0b5803e000      84 r-x-- 0000000000000000 003:00001 libnsl-2.9.so
00007f0b58053000    2044 ----- 0000000000015000 003:00001 libnsl-2.9.so
00007f0b58252000       4 r---- 0000000000014000 003:00001 libnsl-2.9.so
00007f0b58253000       4 rw--- 0000000000015000 003:00001 libnsl-2.9.so
00007f0b58254000       8 rw--- 00007f0b58254000 000:00000   [ anon ]
00007f0b58256000      28 r-x-- 0000000000000000 003:00001 libnss_compat-2.9.so
00007f0b5825d000    2044 ----- 0000000000007000 003:00001 libnss_compat-2.9.so
00007f0b5845c000       4 r---- 0000000000006000 003:00001 libnss_compat-2.9.so
00007f0b5845d000       4 rw--- 0000000000007000 003:00001 libnss_compat-2.9.so
00007f0b5845e000    1324 r-x-- 0000000000000000 003:00001 libc-2.9.so
00007f0b585a9000    2048 ----- 000000000014b000 003:00001 libc-2.9.so
00007f0b587a9000      16 r---- 000000000014b000 003:00001 libc-2.9.so
00007f0b587ad000       4 rw--- 000000000014f000 003:00001 libc-2.9.so
00007f0b587ae000      20 rw--- 00007f0b587ae000 000:00000   [ anon ]
00007f0b587b3000       8 r-x-- 0000000000000000 003:00001 libdl-2.9.so
00007f0b587b5000    2048 ----- 0000000000002000 003:00001 libdl-2.9.so
00007f0b589b5000       4 r---- 0000000000002000 003:00001 libdl-2.9.so
00007f0b589b6000       4 rw--- 0000000000003000 003:00001 libdl-2.9.so
00007f0b589b7000     296 r-x-- 0000000000000000 003:00001 libncurses.so.5.7
00007f0b58a01000    2048 ----- 000000000004a000 003:00001 libncurses.so.5.7
00007f0b58c01000      16 r---- 000000000004a000 003:00001 libncurses.so.5.7
00007f0b58c05000       4 rw--- 000000000004e000 003:00001 libncurses.so.5.7
00007f0b58c06000       4 rw--- 00007f0b58c06000 000:00000   [ anon ]
00007f0b58c07000     116 r-x-- 0000000000000000 003:00001 ld-2.9.so
00007f0b58ded000       8 rw--- 00007f0b58ded000 000:00000   [ anon ]
00007f0b58e1f000      16 rw--- 00007f0b58e1f000 000:00000   [ anon ]
00007f0b58e23000       4 r---- 000000000001c000 003:00001 ld-2.9.so
00007f0b58e24000       4 rw--- 000000000001d000 003:00001 ld-2.9.so
00007fff60e0e000      88 rw--- 00007ffffffe9000 000:00000   [ stack ]
00007fff60ffd000       4 r-x-- 00007fff60ffd000 000:00000   [ anon ]
ffffffffff600000       4 r-x-- 0000000000000000 000:00000   [ anon ]
mapped: 17668K    writeable/private: 600K    shared: 0K




Here are my questions:

Firstly, the "Address" seems too high.  I have 2 GBytes of RAM, which should 
translate to a maximum address of 0x80000000 (8 Hex digits), yet I see 
addresses of "7fff60ffd000" which is 12 Hex digits.

Is this just "virtual" memory, so it can be bigger than actual physical 
memory?  or did they add 3 digits (which are always zeros) to the end for 
some reason?




Also, I am aware of how the goofy X86 architecture has a base address and an 
offset, but I notice that the offset is sometimes exactly equal to the base 
address.  (This can't be a coincidence.)

Can somebody explain what these 2 memory addresses are really telling me?

Thanks!



PS:  Oh my gosh!  This post is "on topic", which is kind of rare for me.   
Hmmmm....   [Thinking Fast!] Actually, my beagle needs to know this!  <grin>







-- 


Casey Bralla
Chief Nerd in Residence
The NerdWorld Organisation
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