Understanding the __libc_init_array

I viewed the source code of __libc_init_array. But I don't quite understand what this function does.

I know that these symbols

/* These magic symbols are provided by the linker.  */
extern void (*__preinit_array_start []) (void) __attribute__((weak));
extern void (*__preinit_array_end []) (void) __attribute__((weak));
extern void (*__init_array_start []) (void) __attribute__((weak));
extern void (*__init_array_end []) (void) __attribute__((weak));
extern void (*__fini_array_start []) (void) __attribute__((weak));
extern void (*__fini_array_end []) (void) __attribute__((weak));

is defined in the linker script.

Part of the linker script may look like:

.preinit_array :
{
  PROVIDE_HIDDEN (__preinit_array_start = .);
  KEEP (*(.preinit_array*))
  PROVIDE_HIDDEN (__preinit_array_end = .);
} >FLASH
.init_array :
{
  PROVIDE_HIDDEN (__init_array_start = .);
  KEEP (*(SORT(.init_array.*)))
  KEEP (*(.init_array*))
  PROVIDE_HIDDEN (__init_array_end = .);
} >FLASH
...

And then I searched with the key "init_array" in the documentation of ELF-v1.1, GCC 4.7.2, ld, and CodeSourcery (I'm using CodeSourcery G++ Lite) only to get nothing.

Where can I find the specification of these symbols?