On 08/04/06, shivaligupta <shivaligupta308@xxxxxxxxx> wrote: > Hi Hareesh! > > Thanks a lot for the help. But my doubt is not what u explained me but > that how two diff processes uses the same shared library? > > Regards > Shivali > > Hareesh Nagarajan wrote: > > > On 4/7/06, *shivaligupta* <shivaligupta308@xxxxxxxxx > > <mailto:shivaligupta308@xxxxxxxxx>> wrote: > > > > Where in memory is shared library loaded? > > i guess it should be in the process virtual address space only but if > > that is the case how another process which wants to use the same > > library > > comes to know that the library has already been loaded and how is it > > able to use that? > > > > > > > > Read the following link: > > http://www.tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html > > > > But, to help you out a little, check this out: > > > > $ cat x.c > > #include <stdio.h> > > > > main() > > { > > printf("hit any key..."); > > getchar(); > > } > > > > $ gcc x.c -ox > > $ ./x > > > > $ readelf -a x | grep getchar > > 0804960c 00000107 R_386_JUMP_SLOT 00000000 getchar > > 1: 00000000 221 FUNC GLOBAL DEFAULT UND getchar@xxxxxxxxx (2) > > 82: 00000000 221 FUNC GLOBAL DEFAULT UND getchar@@GLIBC_2.0 > > > > $ readelf -a x | grep printf > > 08049614 00000307 R_386_JUMP_SLOT 00000000 printf > > 3: 00000000 57 FUNC GLOBAL DEFAULT UND printf@xxxxxxxxx (2) > > 97: 00000000 57 FUNC GLOBAL DEFAULT UND printf@@GLIBC_2.0 > > > > The addresses of printf and getchar are undefined and will be resolved > > at run time. > > > > $readelf -a ./x > > > > [snip] > > 0x00000001 (NEEDED) Shared library: [libc.so.6] > > [snip] > > > > With this hint, ld figures out it needs to load the shared library. > > Let us run program ./x in one terminal and check its process map from > > another. > > > > hareesh@salty:~$ pmap `pgrep ./x` > > 11680: ./x > > 08048000 4K r-x-- /x > > 08049000 4K rw--- /x > > 40000000 88K r-x-- /ld-2.3.2.so <http://2.3.2.so> <--- Loader > > 40016000 4K rw--- /ld-2.3.2.so <http://2.3.2.so> > > 40017000 12K rw--- [ anon ] > > 40022000 1192K r-x-- /libc-2.3.2.so <http://2.3.2.so> <--- glibc > > (code section; perhaps) > > 4014c000 36K rw--- /libc-2.3.2.so <http://2.3.2.so> <--- glibc > > (data section; perhaps) > > 40155000 12K rw--- [ anon ] > > bfffe000 8K rw--- [ stack ] > > ffffe000 4K ----- [ anon ] > > total 1364K > > > > -- > > c u > > > > ./hareesh > > > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
