sysdeps/nios2/start.S

   1 /* Startup code for Nios II
   2    Copyright (C) 1995-2021 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, see
  34    <https://www.gnu.org/licenses/>.  */
  35
  36 /* This is the canonical entry point, usually the first thing in the text
  37    segment.
  38
  39         Note that the code in the .init section has already been run.
  40         This includes _init and _libc_init
  41
  42         The stack pointer, sp, will point to the argument count on the stack.
  43         The initial state of the stack when a userspace process is started is:
  44
  45             Purpose                     Start Address   Length
  46             Unspecified                 High Addresses
  47             Referenced strings, etc.                    Varies
  48             Unspecified
  49             Null auxilliary vector entry                4bytes
  50             Auxilliary vector entries                   8bytes each
  51             NULL terminator for envp                    4bytes
  52             Environment pointers        sp+8+4*argc     4bytes each
  53             NULL terminator for argv    sp+4+4*argc     4bytes
  54             Argument pointers           sp+4            4bytes each
  55             Argument count              sp              4bytes
  56             Unspecified                 Low Addresses
  57
  58         If the application should register a destructor function with atexit,
  59         the pointer will be placed in r4. Otherwise r4 will be zero.
  60
  61         The contents of all other registers are unspecified. User code should
  62         set fp to zero to mark the end of the frame chain.
  63
  64         The auxilliary vector is a series of pairs of 32-bit tag and 32-bit
  65         value, terminated by an AT_NULL tag.
  66 */
  67
  68         .text
  69         .globl _start
  70         .type _start,%function
  71 _start:
  72         /* Set up the global pointer.  */
  73         movhi   gp, %hiadj(_gp)
  74         addi    gp, gp, %lo(_gp)
  75
  76         /* Save the stack pointer.  */
  77         mov     r2, sp
  78
  79         /* Create room on the stack for the fini, rtld_fini and stack_end args
  80            to __libc_start_main. */
  81         subi    sp, sp, 12
  82
  83         /* Push stack_end */
  84         stw     r2, 8(sp)
  85
  86         /* Push rtld_fini */
  87         stw     r4, 4(sp)
  88
  89         /* Set up the GOT pointer.  */
  90         nextpc  r22
  91 1:      movhi   r2, %hiadj(_gp_got - 1b)
  92         addi    r2, r2, %lo(_gp_got - 1b)
  93         add     r22, r22, r2
  94
  95         /* Push fini */
  96         movhi   r8, %call_hiadj(__libc_csu_fini)
  97         addi    r8, r8, %call_lo(__libc_csu_fini)
  98         add     r8, r8, r22
  99         ldw     r8, 0(r8)
 100         stw     r8, 0(sp)
 101
 102         /* r7 == init */
 103         movhi   r7, %call_hiadj(__libc_csu_init)
 104         addi    r7, r7, %call_lo(__libc_csu_init)
 105         add     r7, r7, r22
 106         ldw     r7, 0(r7)
 107
 108         /* r6 == argv */
 109         addi    r6, sp, 16
 110
 111         /* r5 == argc */
 112         ldw     r5, 12(sp)
 113
 114         /* r4 == main */
 115         movhi   r4, %call_hiadj(main)
 116         addi    r4, r4, %call_lo(main)
 117         add     r4, r4, r22
 118         ldw     r4, 0(r4)
 119
 120         /* fp == 0 */
 121         mov     fp, zero
 122
 123         /* __libc_start_main (main, argc, argv, init, fini, rtld_fini,
 124                               stack_end) */
 125
 126         /* Let the libc call main and exit with its return code.  */
 127         movhi   r2, %call_hiadj(__libc_start_main)
 128         addi    r2, r2, %call_lo(__libc_start_main)
 129         add     r2, r2, r22
 130         ldw     r2, 0(r2)
 131         callr   r2
 132
 133         /* should never get here....*/
 134         movhi   r2, %call_hiadj(abort)
 135         addi    r2, r2, %call_lo(abort)
 136         add     r2, r2, r22
 137         ldw     r2, 0(r2)
 138         callr   r2
 139
 140 /* Define a symbol for the first piece of initialized data.  */
 141         .data
 142         .globl __data_start
 143 __data_start:
 144         .long 0
 145         .weak data_start
 146         data_start = __data_start