Home/ Questions/Q 7683959
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-31T18:54:56+00:00

I was trying to see memory map of a process on Linux x86-64 using

  • 0

I was trying to see memory map of a process on Linux x86-64 using pmap -x command. I got confused looking at the output of the pmap. Particularly for the entries for mapping dynamic libraries. There are multiple entries for them (actually 4 for all most all of them, with some having 3 entries). Following is an example

  Address           Kbytes   RSS   Dirty Mode   Mapping

00000036ca200000      88      64       0 r-x--  libpthread-2.5.so
00000036ca216000    2044       0       0 -----  libpthread-2.5.so
00000036ca415000       4       4       4 r----  libpthread-2.5.so
00000036ca416000       4       4       4 rw---  libpthread-2.5.so

The second row for each of the library always has size of 2MB while it has no page permission. Across all libraries it seems its RSS is ALWAYS zero. Last two rows also have same size (which is base page size) and same permissions (a handful libraries does not have rw mapping).

Does anybody has some explanation for this? I am kind of having a sense that possibly the mapping with the read-only protection is done by the loader to read the metadata of the library while the portion with the executable permission actually the code for the library. I may be wrong though.

But I have no clue about that middle row. No permission and no usages? Anyone has some words of wisdom here?

I also saw a few pages reported to be on the anonymous memory and not have any mode bit set. What do these represent?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    First of all , there can be this case that one same process can use more than one memory usage instance. I don’t know if this is what you want to know. I have seen that , while using a browser in Linux, with just one tab open, and using the top command, it shows like more than 4 usage in the memory usage list, covering more than 10mb of memory. I think its ok because of the more number of threads running by the same process.

    This link may be useful, since, in the usage example itself, if you observe, the mapping of the -x command show more number of usage.

    http://www.cyberciti.biz/tips/howto-find-memory-used-by-program.html

    • 0