memset.s

在x86平台上运行不可信任代码的sandbox。

/*
 * Copyright (c) 1993 Winning Strategies, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Winning Strategies, Inc.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <asm.h>

/*
 * memset(void *b, int c, size_t len)
 *	write len bytes of value c (converted to an unsigned char) to 
 *	the string b.
 *
 * Written by:
 *	J.T. Conklin ([e-mail]), Winning Strategies, Inc.
 */

ENTRY(memset)
	pushl	%edi
	pushl	%ebx
	movl	12(%esp),%edi
	movzbl	16(%esp),%eax		/* unsigned char, zero extend */
	movl	20(%esp),%ecx
	pushl	%edi			/* push address of buffer */

	cld				/* set fill direction forward */

	/*
	 * if the string is too short, it's really not worth the overhead
	 * of aligning to word boundries, etc.  So we jump to a plain
	 * unaligned set.
	 */
	cmpl	$0x0f,%ecx
	jle	L1

	movb	%al,%ah			/* copy char to all bytes in word */
	movl	%eax,%edx
	sall	$16,%eax
	orl	%edx,%eax

	movl	%edi,%edx		/* compute misalignment */
	negl	%edx
	andl	$3,%edx
	movl	%ecx,%ebx
	subl	%edx,%ebx

	movl	%edx,%ecx		/* set until word aligned */
	rep
	stosb

	movl	%ebx,%ecx
	shrl	$2,%ecx			/* set by words */
	rep
	stosl

	movl	%ebx,%ecx		/* set remainder by bytes */
	andl	$3,%ecx
L1:	rep
	stosb

	popl	%eax			/* pop address of buffer */
	popl	%ebx
	popl	%edi
	ret