[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: questions about /proc/<pid>/map

On Sun, Oct 06, 2002 at 05:38:24PM -0700, Yue Luo wrote:

>   Is this "offset of mapping" the last argument to mmap()?  

Yes.

>   The following is 2 lines from the memory maps of process sshd:
> 40143000-40166000 r-xp 00000000 08:03 327696    
> /usr/lib/libglib-1.2.so.0.0.10
> 40166000-40167000 rw-p 00022000 08:03 327696    
> /usr/lib/libglib-1.2.so.0.0.10
>   I guess that the first line is for the code segment and the second
> line is for the data.  The offset is 0x22000.  I used "objdump -h" to
> show all the sections of the library.  I found no section starting at
> 0x22000.  So what should be at the offset in the file? Or my newbie's
> understanding is totally wrong? 

Remember that mmap() works in page-sizes only. So if you look for the
nearest section (probably .data) then round it down to the next page
boundary, you'll get your value. For example :

40000000-40015000 r-xp 00000000 03:07 392470     /lib/ld-2.2.so
40015000-40016000 rw-p 00014000 03:07 392470     /lib/ld-2.2.so

 10 .rodata       00001da4  00012de0  00012de0  00012de0  2**5
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 11 .data         000000b8  00015ba0  00015ba0  00014ba0  2**5
                  CONTENTS, ALLOC, LOAD, DATA

The next lowest page boundary from the file offset of .data is 0x14000
(< 0x14ba0), and indeed, that's where we find it mapped from.

regards
john

-- 
"I will eat a rubber tire to the music of The Flight of the Bumblebee"
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive:       http://mail.nl.linux.org/kernelnewbies/
FAQ:           http://kernelnewbies.org/faq/