CODEWITHSUNDEEP
memory-managementprocessvirtual-memorypmapmemory-segmentation
Vikram
Vikram

Reputation: 2069

Questions on Process Map

Here I am running two instance of same program in two different terminals. The process map of them are

In first terminal -

vikram@vikram-Studio-XPS-1645:~$ pmap 6548
6548:   ./a.out
0000000000400000      4K r-x--  /home/vikram/a.out
0000000000600000      4K r----  /home/vikram/a.out
0000000000601000      4K rw---  /home/vikram/a.out
00007f90f2406000   1576K r-x--  /lib/x86_64-linux-gnu/libc-2.13.so
00007f90f2590000   2044K -----  /lib/x86_64-linux-gnu/libc-2.13.so
00007f90f278f000     16K r----  /lib/x86_64-linux-gnu/libc-2.13.so
00007f90f2793000      4K rw---  /lib/x86_64-linux-gnu/libc-2.13.so
00007f90f2794000     24K rw---    [ anon ]
00007f90f279a000    132K r-x--  /lib/x86_64-linux-gnu/ld-2.13.so
00007f90f2992000     12K rw---    [ anon ]
00007f90f29b7000     12K rw---    [ anon ]
00007f90f29ba000      4K r----  /lib/x86_64-linux-gnu/ld-2.13.so
00007f90f29bb000      8K rw---  /lib/x86_64-linux-gnu/ld-2.13.so
00007fffb2333000    132K rw---    [ stack ]
00007fffb23ff000      4K r-x--    [ anon ]
ffffffffff600000      4K r-x--    [ anon ]
 total             3984K

In second terminal - 

vikram@vikram-Studio-XPS-1645:~$ pmap 6676
6676:   ./a.out
0000000000400000      4K r-x--  /home/vikram/a.out
0000000000600000      4K r----  /home/vikram/a.out
0000000000601000      4K rw---  /home/vikram/a.out
00007f3b0ad37000   1576K r-x--  /lib/x86_64-linux-gnu/libc-2.13.so
00007f3b0aec1000   2044K -----  /lib/x86_64-linux-gnu/libc-2.13.so
00007f3b0b0c0000     16K r----  /lib/x86_64-linux-gnu/libc-2.13.so
00007f3b0b0c4000      4K rw---  /lib/x86_64-linux-gnu/libc-2.13.so
00007f3b0b0c5000     24K rw---    [ anon ]
00007f3b0b0cb000    132K r-x--  /lib/x86_64-linux-gnu/ld-2.13.so
00007f3b0b2c3000     12K rw---    [ anon ]
00007f3b0b2e8000     12K rw---    [ anon ]
00007f3b0b2eb000      4K r----  /lib/x86_64-linux-gnu/ld-2.13.so
00007f3b0b2ec000      8K rw---  /lib/x86_64-linux-gnu/ld-2.13.so
00007fffb1153000    132K rw---    [ stack ]
00007fffb11c7000      4K r-x--    [ anon ]
ffffffffff600000      4K r-x--    [ anon ]
 total             3984K

My questions are -

  1. "/lib/x86_64-linux-gnu/ld-2.13.so" this library has two different addresses in terminal 1 and 2 ( 00007f90f279a000 and 00007f3b0b0cb000 ). Is it means this library is loaded 2 times in main memory ?

  2. Assuming a.out is binary of simple Hello_World.c program 

    #include<stdio.h>
void main()
{ printf("Hello World");}

    then which part of a.out has r & w permission ? In simple words which part of source " 0000000000601000 4K rw--- /home/vikram/a.out " this segment is suppose to contain ?

  3. Why anon is not continuous like other segments ?

  4. What " 00007f90f2590000 2044K ----- /lib/x86_64-linux-gnu/libc-2.13.so " this segment suppose to contain .... because it doesn't have read, write, execute permissions.

Upvotes: 0

Views: 379

Answers (1)

Sachin
Sachin

Reputation: 26

1) Dynamic loader or the ld is the first to be executed after OS starts the process. Those address are virtual addresses of the process, but would ultimately map to same physical memory.

2) data segment of the process. (both initialized data and BSS) 3) Its used various purposes such as heap, mmap and any sharedmemory etc. 4) AFAIK its internal private data.

Upvotes: 1

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