Subversion Repositories openrisc_2011-10-31

/*
 * crt0.S -- startup file for MIPS.
 *
 * Copyright (c) 1995, 1996, 1997, 2001 Cygnus Support
 *
 * The authors hereby grant permission to use, copy, modify, distribute,
 * and license this software and its documentation for any purpose, provided
 * that existing copyright notices are retained in all copies and that this
 * notice is included verbatim in any distributions. No written agreement,
 * license, or royalty fee is required for any of the authorized uses.
 * Modifications to this software may be copyrighted by their authors
 * and need not follow the licensing terms described here, provided that
 * the new terms are clearly indicated on the first page of each file where
 * they apply.
 */

#ifdef __mips16
/* This file contains 32 bit assembly code.  */
        .set nomips16
#endif

#include "regs.S"

/*
 * Set up some room for a stack. We just grab a chunk of memory.
 */
#define STACK_SIZE  0x4000
#define GLOBAL_SIZE 0x2000

#define STARTUP_STACK_SIZE      0x0100

/* This is for referencing addresses that are not in the .sdata or
   .sbss section under embedded-pic, or before we've set up gp.  */
#ifdef __mips_embedded_pic
# ifdef __mips64
#  define LA(t,x) la t,x-PICBASE ; daddu t,s0,t
# else
#  define LA(t,x) la t,x-PICBASE ; addu t,s0,t
# endif
#else /* __mips_embedded_pic */
# define LA(t,x) la t,x
#endif /* __mips_embedded_pic */

        .comm   __memsize, 12
        .comm   __lstack, STARTUP_STACK_SIZE

        .text
        .align  2

/* Without the following nop, GDB thinks _start is a data variable.
 * This is probably a bug in GDB in handling a symbol that is at the
 * start of the .text section.
 */
        nop

        .globl  hardware_hazard_hook .text
        .globl  _start
        .ent    _start
_start:
        .set    noreorder
#ifdef __mips_embedded_pic
#define PICBASE start_PICBASE
        PICBASE = .+8
        bal     PICBASE
        nop
        move    s0,$31
#endif
#if __mips<3
#  define STATUS_MASK (SR_CU1|SR_PE)
#else
/* Post-mips2 has no SR_PE bit.  */
#  ifdef __mips64
/* Turn on 64-bit addressing and additional float regs.  */
#    define STATUS_MASK (SR_CU1|SR_FR|SR_KX|SR_SX|SR_UX)
#  else
#    if __mips_fpr==32
#      define STATUS_MASK (SR_CU1)
#    else
/* Turn on additional float regs.  */
#      define STATUS_MASK (SR_CU1|SR_FR)
#    endif
#  endif
#endif
        li      v0, STATUS_MASK
        mtc0    v0, C0_SR
        mtc0    zero, C0_CAUSE
        nop

        /* Avoid hazard from FPU enable and other SR changes.  */
        LA (t0, hardware_hazard_hook)
        beq     t0,zero,1f
        nop
        jal     t0
        nop
1:

/* Check for FPU presence.  Don't check if we know that soft_float is
   being used.  (This also avoids illegal instruction exceptions.)  */

#ifndef __mips_soft_float
        li      t2,0xAAAA5555
        mtc1    t2,fp0          /* write to FPR 0 */
        mtc1    zero,fp1        /* write to FPR 1 */
        mfc1    t0,fp0
        mfc1    t1,fp1
        nop
        bne     t0,t2,1f        /* check for match */
        nop
        bne     t1,zero,1f      /* double check */
        nop
        j       2f              /* FPU is present. */
        nop
#endif
1:
        /* FPU is not present.  Set status register to say that. */
        li      v0, (STATUS_MASK-(STATUS_MASK & SR_CU1))
        mtc0    v0, C0_SR
        nop
        /* Avoid hazard from FPU disable.  */
        LA (t0, hardware_hazard_hook)
        beq     t0,zero,2f
        nop
        jal     t0
        nop
2:


/* Fix high bits, if any, of the PC so that exception handling
   doesn't get confused.  */
        LA (v0, 3f)
        jr      v0
        nop
3:
        LA (gp, _gp)                            # set the global data pointer
        .end _start

/*
 * zero out the bss section.
 */
        .globl  __memsize
        .globl  get_mem_info .text
        .globl  __stack
        .globl  __global
        .ent    zerobss
zerobss:
        LA (v0, _fbss)
        LA (v1, _end)
3:
        sw      zero,0(v0)
        bltu    v0,v1,3b
        addiu   v0,v0,4                         # executed in delay slot

        la      t0, __lstack                    # make a small stack so we
        addiu   sp, t0, STARTUP_STACK_SIZE      # can run some C code
        la      a0, __memsize                   # get the usable memory size
        jal     get_mem_info
        nop

        /* setup the stack pointer */
        LA (t0, __stack)                        # is __stack set ?
        bne     t0,zero,4f
        nop

        /* NOTE: a0[0] contains the amount of memory available, and
                 not the last memory address. */
        la      a0, __memsize
        lw      t0,0(a0)                        # last address of memory available
        la      t1,K0BASE                       # cached kernel memory
        addu    t0,t0,t1                        # get the end of memory address
        /* Allocate 32 bytes for the register parameters.  Allocate 16
           bytes for a null argv and envp.  Round the result up to 64
           bytes to preserve alignment.  */
        subu    t0,t0,64
4:
        move    sp,t0                           # set stack pointer
        .end    zerobss

/*
 * initialize target specific stuff. Only execute these
 * functions it they exist.
 */
        .globl  hardware_init_hook .text
        .globl  software_init_hook .text
        .type   _fini,@function
        .type   _init,@function
        .globl  atexit .text
        .globl  exit .text
        .ent    init
init:
        LA (t9, hardware_init_hook)             # init the hardware if needed
        beq     t9,zero,6f
        nop
        jal     t9
        nop
6:
        LA (t9, software_init_hook)             # init the hardware if needed
        beq     t9,zero,7f
        nop
        jal     t9
        nop
7:
        LA (a0, _fini)
        jal     atexit
        nop

#ifdef GCRT0
        .globl  _ftext
        .globl  _extext
        LA (a0, _ftext)
        LA (a1, _etext)
        jal     monstartup
        nop
#endif


        jal     _init                           # run global constructors
        nop

        addiu   a1,sp,32                        # argv = sp + 32
        addiu   a2,sp,40                        # envp = sp + 40
#if __mips64
        sd      zero,(a1)                       # argv[argc] = 0
        sd      zero,(a2)                       # envp[0] = 0
#else
        sw      zero,(a1)
        sw      zero,(a2)
#endif
        jal     main                            # call the program start function
        move    a0,zero                         # set argc to 0

        # fall through to the "exit" routine
        jal     exit                            # call libc exit to run the G++
                                                # destructors
        move    a0,v0                           # pass through the exit code
        .end    init

 
/* Assume the PICBASE set up above is no longer valid below here.  */
#ifdef __mips_embedded_pic
#undef PICBASE
#endif
        
/*
 * _exit -- Exit from the application. Normally we cause a user trap
 *          to return to the ROM monitor for another run. NOTE: This is
 *          the only other routine we provide in the crt0.o object, since
 *          it may be tied to the "_start" routine. It also allows
 *          executables that contain a complete world to be linked with
 *          just the crt0.o object.
 */
        .globl  hardware_exit_hook .text
        .globl  _exit
        .ent _exit
_exit:
7:
#ifdef __mips_embedded_pic
        /* Need to reinit PICBASE, since we might be called via exit()
           rather than via a return path which would restore old s0.  */
#define PICBASE exit_PICBASE
        PICBASE = .+8
        bal     PICBASE
        nop
        move    s0,$31
#endif
#ifdef GCRT0
        LA (t0, _mcleanup)
        jal     t0
        nop
#endif
        LA (t0, hardware_exit_hook)
        beq     t0,zero,1f
        nop
        jal     t0
        nop
1:

        # break instruction can cope with 0xfffff, but GAS limits the range:
        break   1023
        b       7b                              # but loop back just in-case
        nop
        .end _exit
 
/* Assume the PICBASE set up above is no longer valid below here.  */
#ifdef __mips_embedded_pic
#undef PICBASE
#endif

/* EOF crt0.S */