crt0_cygmon.s

俄罗斯高人Mamaich的Pocket gcc编译器（运行在PocketPC上）的全部源代码。

/*
 * crt0_cygmon.S -- Minimal startup file for MIPS targets running Cygmon.
 *
 * Copyright (c) 1995, 1996, 1997, 2000 Red Hat, Inc.
 *
 * 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.
 */

/*
 * This file contains the minimal startup code necessary.
 * This will not do any hardware initialization.  It is assumed that we are talking to Cygmon
 * and therefore the hardware will be initialized properly.
 */

#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

	.comm	__memsize, 12
	.comm	__lstack, STARTUP_STACK_SIZE
	.comm   __stackbase,4

	.text
	.align	4
    /*
     * 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	_start
	.ent	_start
_start:
	.set	noreorder
	la		gp, _gp					# set the global data pointer, defined in the linker script
	.end	_start

    /*
     * zero out the bss section.
     */
	.globl	__memsize
	.globl	get_mem_info .text
	.globl	zerobss
	.ent	zerobss
zerobss:
	la		v0, _fbss				# These variables are defined in the linker script
	la		v1, _end

3:
	sw		zero, 0(v0)
	bltu	v0, v1, 3b
	addiu	v0, v0, 4				# executed in delay slot

    /*
     * Setup a small stack so we can run some C code,
     * and get the usable memory size.
     */
	la		t0, __lstack
	addiu	sp, t0, STARTUP_STACK_SIZE
	la		a0, __memsize
	jal		get_mem_info
	nop

	/*
     * Setup the stack pointer -- 
     *    get_mem_info returns the top of memory, so just use that In
     *    addition, we must subtract 24 bytes for the 3 8 byte
     *    arguments to main, in case main wants to write them back to
     *    the stack.  The caller is supposed to allocate stack space
     *    for parameters in registers in the old MIPS ABIs.  We must
     *    do this even though we aren't passing arguments, because
     *    main might be declared to have them.
	 *    Some ports need a larger alignment for the stack, so we
	 *    subtract 32, which satisifes the stack for the arguments and
	 *    keeps the stack pointer better aligned.
     */
	subu	v0, v0, 32
	move	sp, v0

	sw		sp, __stackbase			# keep this for future ref
	.end	zerobss

    /*
     * initialize target specific stuff. Only execute these
     * functions it they exist.
     */
	.globl	hardware_init_hook .text
	.globl	software_init_hook .text
	.globl	__do_global_dtors .text
	.globl	atexit .text
	.globl	exit .text
	.globl	init
	.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 software if needed
	beq		t9, zero, 7f
	nop
	jal		t9
	nop
7:
	la		a0, __do_global_dtors
	jal		atexit
	nop

#ifdef GCRT0
	.globl	_ftext
	.globl	_extext
	la		a0, _ftext
	la		a1, _etext
	jal		monstartup
	nop
#endif

	move	a0,zero					# set argc to 0
	jal		main					# call the program start function
	nop

	# 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
	
/*
 * _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	_exit
	.ent	_exit
_exit:
7:
#ifdef GCRT0
	jal		_mcleanup
	nop
#endif
	# Cygmon expects a break 5
	break	5
	nop
	b		7b						# loop back just in-case
	nop
	.end	_exit

/* EOF crt0.S */