Question

I’m dynamically loading some Linux libraries in C.
I can get the start addresses of the libraries using the

dlinfo

(see 1).

I can’t find any information to get the size of a library, however.

The only thing that I’ve found is that one must read the

/proc/[pid]/maps

file and parse it for the relevant information (see 2).
Is there a more elegant method?

Answer 1

(This answer is LINUX/GLIBC specific)

According to http://s.eresi-project.org/inc/articles/elf-rtld.txt

there are link_map *map; map->l_map_start & map->l_map_end

    /* 
        ** Start and finish of memory map for this object.  
    ** l_map_start need not be the same as l_addr.  
    */
    ElfW(Addr) l_map_start, l_map_end;

It is a bit not exact, as said here http://www.cygwin.com/ml/libc-hacker/2007-06/msg00014.html
= some libraries are not continous in memory; the letter linked has some examples… e.g. this is the very internal (to rtld) function to detect is the given address inside lib’s address space or not, based on link_map and direct working with ELF segments:

/* Return non-zero if ADDR lies within one of L's segments.  */
int
internal_function
_dl_addr_inside_object (struct link_map *l, const ElfW(Addr) addr)
{
  int n = l->l_phnum;
  const ElfW(Addr) reladdr = addr - l->l_addr;

  while (--n >= 0)
    if (l->l_phdr[n].p_type == PT_LOAD
    && reladdr - l->l_phdr[n].p_vaddr >= 0
    && reladdr - l->l_phdr[n].p_vaddr < l->l_phdr[n].p_memsz)
      return 1;
  return 0;
}

And this function is the Other alternative, which is to find program headers/ or section headers of ELF loaded (there are some links to such information in link_map)

And the easiest is to use some stat syscall with map->l_name – to read file size from the disk (inexact in detecting huge bss section).