usr/src/lib/libc/i386/gen/alloca.s

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * William Jolitz.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that: (1) source distributions retain this entire copyright
 * notice and comment, and (2) distributions including binaries display
 * the following acknowledgement:  ``This product includes software
 * developed by the University of California, Berkeley and its contributors''
 * in the documentation or other materials provided with the distribution
 * and in all advertising materials mentioning features or use of this
 * software. Neither the name of the University nor the names of its
 * contributors may be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
        .asciz "@(#)alloca.s    5.2 (Berkeley) 5/14/90"
#endif /* LIBC_SCCS and not lint */

/* like alloc, but automatic automatic free in return */

#include "DEFS.h"

ENTRY(alloca)
        popl    %edx            /*  pop return addr */
        popl    %eax            /*  pop amount to allocate */
        movl    %esp,%ecx
        addl    $3,%eax         /*  round up to next word */
        andl    $0xfffffffc,%eax
        subl    %eax,%esp
        movl    %esp,%eax       /* base of newly allocated space */
        pushl   8(%ecx)         /* copy possible saved registers */
        pushl   4(%ecx)
        pushl   0(%ecx)
        pushl   %eax            /* dummy to pop at callsite */
        jmp     %edx            /* "return" */