start.s

一个C源代码分析器

/* Copyright (C) 1994 Free Software Foundation, Inc.
   Contributed by Joel Sherrill ([e-mail]),
     On-Line Applications Research Corporation.
 
This file is part of the GNU C Library.
 
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
 
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.
 
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

/*  entry.s
 *
 *  This file contains the entry point for the application.
 *  The name of this entry point is compiler dependent.
 *  It jumps to the BSP which is responsible for performing
 *  all initialization.
 *
 */

         .text
         .globl  start                  # GNU960 default entry point

start:
        mov     3, r12
        modpc   r12, r12, r12         # enable tracing/trace faults
        mov     g5, g5                # NOP
        mov     0, g14                # initialize constant for C

        /*
         * zero out uninitialized data area
         */
zerobss:
        lda     _end, r4        /* find end of .bss */
        lda     _bss_start, r5  /* find beginning of .bss */
        ldconst 0, r6

loop:   st      r6, (r5)        /* to zero out uninitialized */
        addo    4, r5, r5       /* data area                 */
        cmpobl  r5, r4, loop    /* loop until _end reached   */


        lda     heap_memory, r12      /* tell C lib where heap is */
        st      r12,___C_heap_start
        lda     heap_size, r12        /* tell C lib how big heap is */
        st      r12,___C_heap_size
        lda     stack_memory,r12      /* set up stack pointer: */
        mov     r12, sp
        mov     0, g14           /* initialize constant for C */

        call    init_frames
        ret                      /* return to monitor */

init_frames:
        ldconst 0x3b001000, g0
        ldconst 0x00009107, g1
        modac   g1, g0, g0       /* set AC controls */

        /*
         * Call application mainline.
         *      Someday, real values of argc and argv will be set up.
         *      For now, they are set to 0.
         */

        callx   __Board_Initialize    /* Initialize the board */

        ldconst 0,g0
        ldconst 0,g1
        ldconst 0,g2
        callx   ___libc_init          /* initialize the library and */
                                      /*   call main */
        /*
         * if we return from main, we have "fallen" off the end
         * of the program, therefore status is 0
         * so move 0 to g0 (exit parameter)
         */

        mov     0, g0
        callx   __exit
        ret


/*
 *  Data Declarations.  Start with a macro which helps declare space.
 */

#define DECLARE_SPACE(_name,_space,_align) \
          .globl   _name ; \
          .align   _align ; \
.comm     _name##,_space

#define DECLARE_LABEL(_name) \
          .globl   _name ; \
_name##:  

#define DECLARE_PTR(_name) DECLARE_SPACE(_name,4,2)
#define DECLARE_U32(_name) DECLARE_SPACE(_name,4,2)
#define DECLARE_U16(_name) DECLARE_SPACE(_name,2,1)

/*
 *  Require environment stuff
 */

DECLARE_LABEL(_environ)
DECLARE_PTR(environ)

DECLARE_LABEL(_errno)
DECLARE_U32(errno)

/*
 *  Stack Size and Space
 */

        .set stack_size, 0x20000

DECLARE_SPACE(stack_memory,stack_size,4)
DECLARE_LABEL(stack_end)

/*
 *  Heap Size and Space
 */

        .set heap_size, 0x20000

DECLARE_SPACE(heap_memory,heap_size,4)
DECLARE_LABEL(heap_end)