On Sun, 24 Jan 2010, Mulyadi Santosa wrote:
> On Sun, Jan 24, 2010 at 2:27 PM, ZelluX <zellux@xxxxxxxxx> wrote:
> > So actually dynamic linking has nothing to do with kernel, or
> > there's no special system calls or other mechanisms provided by
> > kernel to support dynamic linking, is it right?
>
> Hi, please, no top posting :)
>
> Yes, kernel has nothing to do with linking. Kernel only helps
> loading the ELF objects...but for linking, it's up to the ld.so
to be specific, if you're asking about what's happening in the
kernel, any shared libraries have to be pulled into the process'
address space and given their own virtual memory area (VMA). how VMAs
work is explained in many places, like robert love's LKD book, chapter
14, "the process address space."
if you have superuser access, you can examine the VMAs for any
process, like examining it for PID 1 (init):
# pmap 1
1: /sbin/init
0000000000400000 132K r-x-- /sbin/init
0000000000621000 4K rw--- /sbin/init
0000000000a9e000 200K rw--- [ anon ]
00000039aae00000 120K r-x-- /lib64/ld-2.11.1.so
00000039ab01d000 4K r---- /lib64/ld-2.11.1.so
00000039ab01e000 4K rw--- /lib64/ld-2.11.1.so
00000039ab01f000 4K rw--- [ anon ]
00000039ab200000 1468K r-x-- /lib64/libc-2.11.1.so
00000039ab36f000 2048K ----- /lib64/libc-2.11.1.so
00000039ab56f000 16K r---- /lib64/libc-2.11.1.so
00000039ab573000 4K rw--- /lib64/libc-2.11.1.so
00000039ab574000 20K rw--- [ anon ]
00007f8397841000 12K rw--- [ anon ]
00007f8397864000 4K rw--- [ anon ]
00007fff890e2000 84K rw--- [ stack ]
00007fff891ff000 4K r-x-- [ anon ]
ffffffffff600000 4K r-x-- [ anon ]
total 4132K
#
note how the process' address space clearly incorporates VMAs for
the shared libs it needs.
if you're asking about what happens in user space, that's really a
different question for a different mailing list.
rday
--
========================================================================
Robert P. J. Day Waterloo, Ontario, CANADA
Linux Consulting, Training and Kernel Pedantry.
Web page: http://crashcourse.ca
Twitter: http://twitter.com/rpjday
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