sysdeps/arm/elf/start.S

   1 /* Startup code for ARM & ELF
   2    Copyright (C) 1995, 1996, 1997, 1998, 2001, 2002 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    In addition to the permissions in the GNU Lesser General Public
  11    License, the Free Software Foundation gives you unlimited
  12    permission to link the compiled version of this file with other
  13    programs, and to distribute those programs without any restriction
  14    coming from the use of this file. (The GNU Lesser General Public
  15    License restrictions do apply in other respects; for example, they
  16    cover modification of the file, and distribution when not linked
  17    into another program.)
  18
  19    Note that people who make modified versions of this file are not
  20    obligated to grant this special exception for their modified
  21    versions; it is their choice whether to do so. The GNU Lesser
  22    General Public License gives permission to release a modified
  23    version without this exception; this exception also makes it
  24    possible to release a modified version which carries forward this
  25    exception.
  26
  27    The GNU C Library is distributed in the hope that it will be useful,
  28    but WITHOUT ANY WARRANTY; without even the implied warranty of
  29    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  30    Lesser General Public License for more details.
  31
  32    You should have received a copy of the GNU Lesser General Public
  33    License along with the GNU C Library; if not, write to the Free
  34    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  35    02111-1307 USA.  */
  36
  37 /* This is the canonical entry point, usually the first thing in the text
  38    segment.
  39
  40         Note that the code in the .init section has already been run.
  41         This includes _init and _libc_init
  42
  43
  44         At this entry point, most registers' values are unspecified, except:
  45
  46    a1           Contains a function pointer to be registered with `atexit'.
  47                 This is how the dynamic linker arranges to have DT_FINI
  48                 functions called for shared libraries that have been loaded
  49                 before this code runs.
  50
  51    sp           The stack contains the arguments and environment:
  52                 0(sp)                   argc
  53                 4(sp)                   argv[0]
  54                 ...
  55                 (4*argc)(sp)            NULL
  56                 (4*(argc+1))(sp)        envp[0]
  57                 ...
  58                                         NULL
  59 */
  60
  61         .text
  62         .globl _start
  63         .type _start,#function
  64 _start:
  65         /* Fetch address of fini */
  66         ldr ip, =__libc_csu_fini
  67
  68         /* Clear the frame pointer since this is the outermost frame.  */
  69         mov fp, #0
  70
  71         /* Pop argc off the stack and save a pointer to argv */
  72         ldr a2, [sp], #4
  73         mov a3, sp
  74
  75         /* Push stack limit */
  76         str a3, [sp, #-4]!
  77
  78         /* Push rtld_fini */
  79         str a1, [sp, #-4]!
  80
  81         /* Set up the other arguments in registers */
  82         ldr a1, =main
  83         ldr a4, =__libc_csu_init
  84
  85         /* Push fini */
  86         str ip, [sp, #-4]!
  87
  88         /* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end) */
  89
  90         /* Let the libc call main and exit with its return code.  */
  91         bl __libc_start_main
  92
  93         /* should never get here....*/
  94         bl abort
  95
  96 /* Define a symbol for the first piece of initialized data.  */
  97         .data
  98         .globl __data_start
  99 __data_start:
 100         .long 0
 101         .weak data_start
 102         data_start = __data_start