On Sat Apr 5 17:33:23 EDT 2014, gary kong wrote:
I am looking at the /proc/self/maps file. i find that for every shared library there are 4 sections with different permission. what are the reasons for this ? does that mean the same library is loaded 4 times ? e.g.
7fb543e5d000-7fb54401a000 r-xp 00000000 08:01 6033115 /lib/x86_64-linux-gnu/libc-2.17.so 7fb54401a000-7fb54421a000 ---p 001bd000 08:01 6033115 /lib/x86_64-linux-gnu/libc-2.17.so 7fb54421a000-7fb54421e000 r--p 001bd000 08:01 6033115 /lib/x86_64-linux-gnu/libc-2.17.so 7fb54421e000-7fb544220000 rw-p 001c1000 08:01 6033115 /lib/x86_64-linux-gnu/libc-2.17.so 7fb544220000-7fb544225000 rw-p 00000000 00:00 0 7fb544225000-7fb54423a000 r-xp 00000000 08:01 6029447 /lib/x86_64-linux-gnu/libgcc_s.so.1 7fb54423a000-7fb544439000 ---p 00015000 08:01 6029447 /lib/x86_64-linux-gnu/libgcc_s.so.1 7fb544439000-7fb54443a000 r--p 00014000 08:01 6029447 /lib/x86_64-linux-gnu/libgcc_s.so.1 7fb54443a000-7fb54443b000 rw-p 00015000 08:01 6029447 /lib/x86_64-linux-gnu/libgcc_s.so.1 7fb54443b000-7fb54453e000 r-xp 00000000 08:01 6032973 /lib/x86_64-linux-gnu/libm-2.17.so 7fb54453e000-7fb54473d000 ---p 00103000 08:01 6032973 /lib/x86_64-linux-gnu/libm-2.17.so 7fb54473d000-7fb54473e000 r--p 00102000 08:01 6032973 /lib/x86_64-linux-gnu/libm-2.17.so 7fb54473e000-7fb54473f000 rw-p 00103000 08:01 6032973 /lib/x86_64-linux-gnu/libm-2.17.so
Gary
Hi Gary, My details below may be a bit sketchy but it means that each library is made up of four parts - * The read ony executable part (r-xp) is the text section, containing the executable code. * The no permissions (---p) part is (probably...?) kernel specific (something to do with faster syscalls?). * The read only non-executable part (r--p) is the data segment for static, read only data and the bss. * The read write part (rw-p) is for dynamic data that the library uses. The 'pmap' command gives this info in a slightly easier to read way. Hope that helps, Mark