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
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