问题
I'm looking at proc/ID/maps under embedded Linux, And I've noticed that some shared libraries appear few times at the memory map of a process why is it so ?
40094000-400d9000 r-xp 00000000 b3:09 723 /system/lib/libc.so
400d9000-400da000 ---p 00000000 00:00 0
400da000-400dc000 r-xp 00045000 b3:09 723 /system/lib/libc.so
400dc000-400de000 rwxp 00047000 b3:09 723 /system/lib/libc.so
400de000-400e9000 rwxp 00000000 00:00 0
400e9000-400ed000 r-xp 00000000 b3:09 770 /system/lib/libgccdemangle.so
400ed000-400ee000 ---p 00000000 00:00 0
400ee000-400ef000 r-xp 00004000 b3:09 770 /system/lib/libgccdemangle.so
400ef000-400f0000 rwxp 00005000 b3:09 770 /system/lib/libgccdemangle.so
40102000-40103000 r-xp 00000000 b3:09 869 /system/lib/libstdc++.so
40103000-40104000 r-xp 00000000 b3:09 869 /system/lib/libstdc++.so
40104000-40105000 rwxp 00001000 b3:09 869 /system/lib/libstdc++.so
40105000-40112000 r-xp 00000000 b3:09 738 /system/lib/libcutils.so
40112000-40113000 r-xp 0000c000 b3:09 738 /system/lib/libcutils.so
40113000-40114000 rwxp 0000d000 b3:09 738 /system/lib/libcutils.so
回答1:
Because an ELF shared library has, like an executable, several segments: often a "text" read only segment (which is mmap -ed shared, so all processes using that segment share some physical RAM), and a "data" read write segment (for static or "global" variables, and perhaps also the PLT...), private to each process.
This is explained in great detail in Drepper's paper: How to write a shared library
来源：https://stackoverflow.com/questions/20969109/why-proc-id-maps-has-multiple-entries-for-shared-libraries