Hi, The segments of shared libraries are not mapped independently. First all the segments are mapped as a single VMA(virtual memory area) calling mmap(). Then mprotect() is called and this single large region is broken into text, data, bss regions. This happens only with shared libraries. But while mapping executables and interpreter (dynamic linker) each segment is mapped one after another.. i.e first text segment, then data segment and then bss segment. Why are shared libaries mapped in such differnt way? Why is mprotect() called?? Lets us see this with an example. The following is obtained from /proc/1/maps 08048000-0804f000 r-xp 00000000 03:01 29220 /sbin/init 0804f000-08051000 rw-p 00006000 03:01 29220 /sbin/init 08051000-08055000 rwxp 00000000 00:00 0 40000000-40015000 r-xp 00000000 03:01 215881 /lib/ld-2.2.4.so 40015000-40016000 rw-p 00014000 03:01 215881 /lib/ld-2.2.4.so 40016000-40017000 rw-p 00000000 00:00 0 4002c000-40161000 r-xp 00000000 03:01 217078 /lib/libc-2.2.4.so 40161000-40166000 rw-p 00134000 03:01 217078 /lib/libc-2.2.4.so 40166000-4016a000 rw-p 00000000 00:00 0 bfffe000-c0000000 rwxp fffff000 00:00 0 Here the libc library, using mmap(), is mapped into region from 4002c000-4016a000. Then mprotect is called. As a result one VMA region form 4002c000-4016a000 is broken into three i.e 4002c000-40161000, 40161000-40166000, 40166000-4016a000. I you know any URl which explains how libraries are mapped please let me know. Thank you in advance, KR ===== "Conquering Myselves to Conquer The World" "Securing Kernel to Secure Whole System" __________________________________________________ Do you Yahoo!? Yahoo! Web Hosting - Let the expert host your site http://webhosting.yahoo.com -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
