GCC

• –as-needed - do not load symbols from libraries specified in command line when they are not needed. This option couses many unresolved symbol errors when order of libraries specified in command line is not correct. http://savannah.gnu.org/forum/forum.php?forum_id=5655

• –hash-style - insert faster GNU hash table instead of SysV table. But looses compatiblity with older systems. http://stackoverflow.com/questions/11741816/only-one-hash-style-in-embedded-linux-why

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Using_ld_the_GNU_Linker/assignments.html [[https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Using_ld_the_GNU_Linker/sections.html https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Using_ld_the_GNU_Linker/expressions.html https://ftp.gnu.org/pub/old-gnu/Manuals/ld-2.9.1/html_node/ld_21.html https://sourceware.org/binutils/docs-2.27/ld/Builtin-Functions.html http://www.math.utah.edu/docs/info/ld_3.html

.crc 0x7FFE : {   KEEP(*(.crc))  }

or

  .crc (ORIGIN(rom)+LENGTH(rom)-2):
  {
     _crcstart = .;
    KEEP(*(.crc))
    _crcend = .;
  } >rom

const uint32_t crcValue __attribute__ ((section (".crc")))     = 0xDEADBEEF;

    .bss :
    {
        _bss = .;
        *(EXCLUDE_FILE (*redoznes.co) .bss*)
/*        *(.bss*)*/
        *(COMMON)
        _ebss = .;
    } > SRAM
    
   ._user_heap_stack :
    {
      *redzones.co(.bss.redzone1)
      . = ALIGN(4);
      end = .;
      _heap = .; /* "end" for newlib's syscalls, "_heap" for sbrk heap boundary checks */
      . = . + _Min_Heap_Size;
      _eheap = .;
      *redoznes.co(.bss.redzone2)
      . = . + _Min_Stack_Size;
      . = ALIGN(4);
    } > SRAM

      _redzone2_begin = .;
      . = . + 16;
      _redzone2_end = .;

and access them from C code:

extern uint8_t _redzone1_begin;
extern uint8_t _redzone1_end;
...
checkRedzone(&_redzone1_begin, &_redzone1_end - &_redzone1_begin);

     empty_ram_size = _estack - ABSOLUTE(.) - _Min_Stack_Size - 16;
      . = . + empty_ram_size;

int foo(int i) __attribute__((optimize("-O3")));