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/************************************************************************************
* arch/arm/src/armv6-m/vfork.S
*
* Copyright (C) 2013 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* 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. Neither the name NuttX 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 BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "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
* COPYRIGHT OWNER OR CONTRIBUTORS 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.
*
************************************************************************************/
/************************************************************************************
* Included Files
************************************************************************************/
#include <nuttx/config.h>
#include "up_vfork.h"
/************************************************************************************
* Pre-processor Definitions
************************************************************************************/
/************************************************************************************
* Global Symbols
************************************************************************************/
.cpu cortex-m0
.file "vfork.S"
.globl up_vfork
/************************************************************************************
* Public Functions
************************************************************************************/
/************************************************************************************
* Name: vfork
*
* Description:
* The vfork() function has the same effect as fork(), except that the behavior is
* undefined if the process created by vfork() either modifies any data other than
* a variable of type pid_t used to store the return value from vfork(), or returns
* from the function in which vfork() was called, or calls any other function before
* successfully calling _exit() or one of the exec family of functions.
*
* This thin layer implements vfork by simply calling up_vfork() with the vfork()
* context as an argument. The overall sequence is:
*
* 1) User code calls vfork(). vfork() collects context information and
* transfers control up up_vfork().
* 2) up_vfork()and calls task_vforksetup().
* 3) task_vforksetup() allocates and configures the child task's TCB. This
* consists of:
* - Allocation of the child task's TCB.
* - Initialization of file descriptors and streams
* - Configuration of environment variables
* - Setup the intput parameters for the task.
* - Initialization of the TCB (including call to up_initial_state()
* 4) up_vfork() provides any additional operating context. up_vfork must:
* - Allocate and initialize the stack
* - Initialize special values in any CPU registers that were not
* already configured by up_initial_state()
* 5) up_vfork() then calls task_vforkstart()
* 6) task_vforkstart() then executes the child thread.
*
* Input Paremeters:
* None
*
* Return:
* Upon successful completion, vfork() returns 0 to the child process and returns
* the process ID of the child process to the parent process. Otherwise, -1 is
* returned to the parent, no child process is created, and errno is set to
* indicate the error.
*
************************************************************************************/
.align 2
.code 16
.thumb_func
.globl vfork
.type vfork, function
vfork:
/* Create a stack frame */
mov r0, sp /* Save the value of the stack on entry */
sub sp, sp, #VFORK_SIZEOF /* Allocate the structure on the stack */
/* CPU registers */
/* Save the volatile registers */
mov r1, sp
stmia r1!, {r4-r7} /* Save r4-r7 in the structure */
mov r4, r8 /* Copy high registers to low registers */
mov r5, r9
mov r6, r10
mov r7, fp
stmia r1!, {r4-r7} /* Save r8-r10 and fp in the structure */
mov r5, lr /* Copy lr to a low register */
stmia r1!, {r0,r5} /* Save sp and lr in the structure */
/* Then, call up_vfork(), passing it a pointer to the stack structure */
mov r0, sp
bl up_vfork
/* Recover r4-r7 that were destroyed before up_vfork was called */
mov r1, sp
ldmia r1!, {r4-r7}
/* Release the stack data and return the value returned by up_vfork */
ldr r1, [sp, #VFORK_LR_OFFSET]
mov r14, r1
add sp, sp, #VFORK_SIZEOF
bx lr
.size vfork, .-vfork
.end
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