Understanding Linux proc id maps

Question

I am trying to understand my embedded Linux application s memory use   The  proc pid maps utility file seems to be a good resource for seeing the details   Unfortunately I don t understand all the columns and entries   What does the anonymous inode 0 entries mean   These seem to be some of the larger memory segments

User · Answer

Please check  http   man7 org linux man-pages man5 proc 5 html  address           perms offset  dev   inode       pathname 00400000-00452000 r-xp 00000000 08 02 173521       usr bin dbus-daemon   The address field is the address space in the process that the mapping occupies     The perms field is a set of permissions    r   read  w   write  x   execute  s   shared  p   private  copy on write    The offset field is the offset into the file whatever    dev is the device  major minor     inode is the inode on that device 0 indicates that no inode is associated with the memoryregion  as would be the case with BSS  uninitialized data    The pathname field will usually be the file that is backing the mapping   For ELF files  you can easily coordinate with the offset field by looking at the Offset field in the ELF program headers  readelf -l    Under Linux 2 0  there is no field giving pathname

User · Answer

memory mapping is not only used to map files into memory but is also a tool to request RAM from kernel  These are those inode 0 entries - your stack  heap  bss segments and more

User · Answer

Each row in  proc  PID maps describes a region of contiguous virtual memory in a process or thread  Each row has the following fields   address           perms offset  dev   inode   pathname 08048000-08056000 r-xp 00000000 03 0c 64593    usr sbin gpm    address - This is the starting and ending address of the region in the process s address space permissions - This describes how pages in the region can be accessed  There are four different permissions  read  write  execute  and shared  If read write execute are disabled  a - will appear instead of the r w x  If a region is not shared  it is private  so a p will appear instead of an s  If the process attempts to access memory in a way that is not permitted  a segmentation fault is generated  Permissions can be changed using the mprotect system call  offset - If the region was mapped from a file  using mmap   this is the offset in the file where the mapping begins  If the memory was not mapped from a file  it s just 0  device - If the region was mapped from a file  this is the major and minor device number  in hex  where the file lives  inode - If the region was mapped from a file  this is the file number  pathname - If the region was mapped from a file  this is the name of the file  This field is blank for anonymous mapped regions  There are also special regions with names like  heap    stack   or  vdso    vdso  stands for virtual dynamic shared object  It s used by system calls to switch to kernel mode  Here s a good article about it   What is linux-gate so 1     You might notice a lot of anonymous regions  These are usually created by mmap but are not attached to any file  They are used for a lot of miscellaneous things like shared memory or buffers not allocated on the heap  For instance  I think the pthread library uses anonymous mapped regions as stacks for new threads

[linux] Understanding Linux /proc/id/maps

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