usr/src/lib/crt/amd64/mach-crt1.s

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26
  27 #include <sys/asm_linkage.h>
  28
  29         .file   "mach-crt1.s"
  30
  31         .global _start_crt
  32
  33 /*
  34  *   The SVR4/i386 ABI (pages 3-29) says that when the entry
  35  *   point runs registers' %rbp, %rsp, %rdx values are specified
  36  *   the following:
  37  *
  38  *      %rbp The content of this register is unspecified at
  39  *              process initialization time, but the user code should mark
  40  *              the deepest stack frame by setting the frame pointer to zero.
  41  *              No other frame's %ebp should have a zero value.
  42  *
  43  *      %rsp Performing its usual job, the stack pointer holds the address
  44  *      of the bottom of the stack, which is guaranteed to be
  45  *      quadword aligned.
  46  *
  47  *              The stack contains the arguments and environment:
  48  *        ...
  49  *        envp[0]               (16+(8*argc))(%rsp)
  50  *        NULL                  (8+(8*argc))(%rsp)
  51  *        ...
  52  *        argv[0]               8(%rsp)
  53  *        argc                  0(%rsp)
  54  *
  55  *      %rdx In a conforming program, this register contains a function
  56  *              pointer that the application should register with atexit(BA_OS).
  57  *              This function is used for shared object termination code
  58  *              [see Dynamic Linking in Chapter 5 of the System V ABI].
  59  *
  60  */
  61
  62 ENTRY_NP(_start)
  63 /*
  64  * Allocate a NULL return address and a NULL previous %rbp as if
  65  * there was a genuine call to _start.
  66  */
  67         pushq   $0
  68         pushq   $0
  69         movq    %rsp,%rbp               /* The first stack frame */
  70
  71 /*
  72  * The stack now is
  73  *
  74  *        envp[0]               (32+(8*argc))(%rsp)      - (A)
  75  *        NULL                  (24+(8*argc))(%rsp)
  76  *        ...
  77  *        argv[0]               24(%rbp)                 - (B)
  78  *        argc                  16(%rbp)
  79  *        0                     8(%rbp)
  80  *        0                     0(%rbp)
  81  */
  82
  83         andq    $-16,%rsp               /* align the stack */
  84         movq    16(%rbp),%rdi           /* argc */
  85         leaq    24(%rbp),%rsi           /* argv */
  86         /* NB: rt_do_exit, if applicable, is already in %rdx */
  87         call    _start_crt
  88         hlt
  89 SET_SIZE(_start)
  90
  91 /*
  92  * The following is here in case any object module compiled with cc -p
  93  *      was linked into this module.
  94  */
  95 ENTRY_NP(_mcount)
  96         .weak   _mcount
  97         ret
  98 SET_SIZE(_mcount)