sysdeps/mips/start.S

   1 /* Startup code compliant to the ELF Mips ABI.
   2    Copyright (C) 1995-2014 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    <http://www.gnu.org/licenses/>.  */
  35
  36 #define __ASSEMBLY__ 1
  37 #include <entry.h>
  38 #include <sgidefs.h>
  39 #include <sys/asm.h>
  40
  41 #ifndef ENTRY_POINT
  42 #error ENTRY_POINT needs to be defined for start.S on MIPS/ELF.
  43 #endif
  44
  45 /* This is the canonical entry point, usually the first thing in the text
  46    segment.  The SVR4/Mips ABI (pages 3-31, 3-32) says that when the entry
  47    point runs, most registers' values are unspecified, except for:
  48
  49    v0 ($2)      Contains a function pointer to be registered with `atexit'.
  50                 This is how the dynamic linker arranges to have DT_FINI
  51                 functions called for shared libraries that have been loaded
  52                 before this code runs.
  53
  54    sp ($29)     The stack contains the arguments and environment:
  55                 0(%esp)                 argc
  56                 4(%esp)                 argv[0]
  57                 ...
  58                 (4*argc)(%esp)          NULL
  59                 (4*(argc+1))(%esp)      envp[0]
  60                 ...
  61                                         NULL
  62    ra ($31)     The return address register is set to zero so that programs
  63                 that search backword through stack frames recognize the last
  64                 stack frame.
  65 */
  66
  67
  68 /* We need to call:
  69    __libc_start_main (int (*main) (int, char **, char **), int argc,
  70                       char **argv, void (*init) (void), void (*fini) (void),
  71                       void (*rtld_fini) (void), void *stack_end)
  72 */
  73
  74         .text
  75         .globl ENTRY_POINT
  76         .type ENTRY_POINT,@function
  77 #ifndef __mips16
  78 ENTRY_POINT:
  79 # ifdef __PIC__
  80         SETUP_GPX($0)
  81         SETUP_GPX64($25,$0)
  82 # else
  83         PTR_LA $28, _gp         /* Setup GP correctly if we're non-PIC.  */
  84         move $31, $0
  85 # endif
  86
  87         PTR_LA $4, main         /* main */
  88         PTR_L $5, 0($29)                /* argc */
  89         PTR_ADDIU $6, $29, PTRSIZE      /* argv  */
  90
  91         /* Allocate space on the stack for seven arguments (o32 only)
  92            and make sure the stack is aligned to double words (8 bytes)
  93            on o32 and quad words (16 bytes) on n32 and n64.  */
  94
  95         and $29, -2 * SZREG
  96 # if _MIPS_SIM == _ABIO32
  97         PTR_SUBIU $29, 32
  98 # endif
  99         PTR_LA $7, __libc_csu_init              /* init */
 100         PTR_LA $8, __libc_csu_fini
 101 # if _MIPS_SIM == _ABIO32
 102         PTR_S $8, 16($29)               /* fini */
 103         PTR_S $2, 20($29)               /* rtld_fini */
 104         PTR_S $29, 24($29)              /* stack_end */
 105 # else
 106         move $9, $2             /* rtld_fini */
 107         move $10, $29           /* stack_end */
 108 # endif
 109         jal __libc_start_main
 110 hlt:    b hlt                   /* Crash if somehow it does return.  */
 111
 112 #elif _MIPS_SIM == _ABIO32 /* __mips16 */
 113         /* MIPS16 entry point.  */
 114         .set    mips16
 115 ENTRY_POINT:
 116 # ifdef __PIC__
 117         li      $3, %hi(_gp_disp)
 118         addiu   $4, $pc, %lo(_gp_disp)
 119         sll     $3, 16
 120         addu    $3, $4
 121         move    $gp, $3
 122 # else
 123         li      $3, %hi(_gp)
 124         sll     $3, 16
 125         addiu   $3, %lo(_gp)
 126         move    $gp, $3
 127 # endif
 128         /* Tie end of stack frames.  */
 129         li      $4, 0
 130         move    $31, $4
 131         /* Create new SP value in $7, including alignment.  */
 132         li      $4, 2 * SZREG
 133         neg     $4, $4
 134         move    $7, $sp
 135         and     $7, $4
 136         addiu   $7, -32
 137         /* Load arguments with original SP.  */
 138         lw      $5, 0($sp)
 139         addiu   $6, $sp, PTRSIZE
 140         /* Update SP.  */
 141         move    $sp, $7
 142         /* Lay out last arguments, and call __libc_start_main().  */
 143 # ifdef __PIC__
 144         sw      $7, 24($sp)                     /* stack_end */
 145         lw      $4, %got(__libc_csu_fini)($3)
 146         lw      $7, %got(__libc_csu_init)($3)   /* init */
 147         sw      $4, 16($sp)                     /* fini */
 148         lw      $4, %got(main)($3)              /* main */
 149         lw      $3, %call16(__libc_start_main)($3)
 150         sw      $2, 20($sp)                     /* rtld_fini */
 151         move    $25, $3
 152         jalr    $3
 153 # else
 154         lw      $4, 1f
 155         sw      $7, 24($sp)                     /* stack_end */
 156         lw      $7, 2f                          /* init */
 157         sw      $4, 16($sp)                     /* fini */
 158         lw      $4, 3f                          /* main */
 159         sw      $2, 20($sp)                     /* rtld_fini */
 160         jal     __libc_start_main
 161 # endif
 162 hlt:    b       hlt             /* Crash if somehow it does return.  */
 163 # ifndef __PIC__
 164         .align  2
 165 1:      .word   __libc_csu_fini
 166 2:      .word   __libc_csu_init
 167 3:      .word   main
 168 # endif
 169
 170 #else /* __mips16 && _MIPS_SIM != _ABIO32 */
 171 # error "MIPS16 support for N32/N64 not implemented"
 172
 173 #endif /* __mips16 */
 174
 175 /* Define a symbol for the first piece of initialized data.  */
 176         .data
 177         .globl __data_start
 178 __data_start:
 179         .long 0
 180         .weak data_start
 181         data_start = __data_start