RTEMS Logo

RTEMS 4.8.0 On-Line Library


Linker Script Example Linker Command Script

PREV UP NEXT Bookshelf BSP and Device Driver Development Guide

4.4: Example Linker Command Script

The GNU linker has a command language to specify the image format. This command language can be quite complicated but most of what is required can be learned by careful examination of a well-documented example. The following is a heavily commented version of the linker script used with the the gen68340 BSP This file can be found at $BSP340_ROOT/startup/linkcmds.

/*
 *  Specify that the output is to be coff-m68k regardless of what the
 *  native object format is.
 */

OUTPUT_FORMAT(coff-m68k)

/*
 *  Set the amount of RAM on the target board.
 *
 *  NOTE: The default may be overridden by passing an argument to ld.
 */

RamSize = DEFINED(RamSize) ? RamSize : 4M;

/*
 *  Set the amount of RAM to be used for the application heap.  Objects
 *  allocated using malloc() come from this area.  Having a tight heap
 *  size is somewhat difficult and multiple attempts to squeeze it may
 *  be needed reducing memory usage is important.  If all objects are
 *  allocated from the heap at system initialization time, this eases
 *  the sizing of the application heap.
 *
 *  NOTE 1: The default may be overridden by passing an argument to ld.
 *
 *  NOTE 2: The TCP/IP stack requires additional memory in the Heap.
 *
 *  NOTE 3: The GNAT/RTEMS run-time requires additional memory in
 *  the Heap.
 */

HeapSize = DEFINED(HeapSize) ? HeapSize : 0x10000;

/*
 *  Set the size of the starting stack used during BSP initialization
 *  until first task switch.  After that point, task stacks allocated
 *  by RTEMS are used.
 *
 *  NOTE: The default may be overridden by passing an argument to ld.
 */

StackSize = DEFINED(StackSize) ? StackSize : 0x1000;

/*
 *  Starting addresses and length of RAM and ROM.
 *
 *  The addresses must be valid addresses on the board.  The
 *  Chip Selects should be initialized such that the code addresses
 *  are valid.
 */

MEMORY {
    ram : ORIGIN = 0x10000000, LENGTH = 4M
    rom : ORIGIN = 0x01000000, LENGTH = 4M
}

/*
 *  This is for the network driver.  See the Networking documentation
 *  for more details.
 */

ETHERNET_ADDRESS =
   DEFINED(ETHERNET_ADDRESS) ? ETHERNET_ADDRESS : 0xDEAD12;

/*
 *  The following defines the order in which the sections should go.
 *  It also defines a number of variables which can be used by the
 *  application program.
 *
 *  NOTE: Each variable appears with 1 or 2 leading underscores to
 *        ensure that the variable is accessible from C code with a
 *        single underscore.  Some object formats automatically add
 *        a leading underscore to all C global symbols.
 */

SECTIONS {

  /*
   *  Make the RomBase variable available to the application.
   */

  _RamSize = RamSize;
  __RamSize = RamSize;

  /*
   *  Boot PROM  - Set the RomBase variable to the start of the ROM.
   */

  rom : {
    _RomBase = .;
    __RomBase = .;
  } >rom

  /*
   * Dynamic RAM - set the RamBase variable to the start of the RAM.
   */

  ram : {
    _RamBase = .;
    __RamBase = .;
  } >ram

  /*
   *  Text (code) goes into ROM
   */

  .text : {
    /*
     *  Create a symbol for each object (.o).
     */

    CREATE_OBJECT_SYMBOLS

    /*
     *  Put all the object files code sections here.
     */

    *(.text)

    . = ALIGN (16);      /*  go to a 16-byte boundary */

    /*
     *  C++ constructors and destructors
     *
     *  NOTE:  See the CROSSGCC mailing-list FAQ for
     *         more details about the "[......]".
     */

    __CTOR_LIST__ = .;
   [......]
    __DTOR_END__ = .;

    /*
     *  Declares where the .text section ends.
     */

    etext = .;
    _etext = .;
  } >rom

  /*
   *  Exception Handler Frame section
   */

  .eh_fram : {
    . = ALIGN (16);
    *(.eh_fram)
  } >ram

  /*
   *  GCC Exception section
   */

  .gcc_exc : {
    . = ALIGN (16);
    *(.gcc_exc)
  } >ram

  /*
   *  Special variable to let application get to the dual-ported
   *  memory.
   */

  dpram : {
    m340 = .;
    _m340 = .;
    . += (8 * 1024);
  } >ram

  /*
   *  Initialized Data section goes in RAM
   */

  .data : {
    copy_start = .;
    *(.data)

    . = ALIGN (16);
    _edata = .;
    copy_end = .;
  } >ram

  /*
   *  Uninitialized Data section goes in ROM
   */

  .bss : {
    /*
     *  M68K specific: Reserve some room for the Vector Table
     *  (256 vectors of 4 bytes).
     */

    M68Kvec = .;
    _M68Kvec = .;
    . += (256 * 4);

    /*
     *  Start of memory to zero out at initialization time.
     */

    clear_start = .;

    /*
     *  Put all the object files uninitialized data sections
     *  here.
     */

    *(.bss)

    *(COMMON)

    . = ALIGN (16);
    _end = .;

    /*
     *  Start of the Application Heap
     */

    _HeapStart = .;
    __HeapStart = .;
    . += HeapSize;

    /*
     *  The Starting Stack goes after the Application Heap.
     *  M68K stack grows down so start at high address.
     */

    . += StackSize;
    . = ALIGN (16);
    stack_init = .;

    clear_end = .;

    /*
     *  The RTEMS Executive Workspace goes here.  RTEMS
     *  allocates tasks, stacks, semaphores, etc. from this
     *  memory.
     */

    _WorkspaceBase = .;
    __WorkspaceBase = .;
  } >ram
}


PREV UP NEXT Bookshelf BSP and Device Driver Development Guide

Copyright © 1988-2007OAR Corporation