/****************************************************************************
* arch/arm/src/common/up_vfork.c
*
* 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 <stdint.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
#include <nuttx/sched.h>
#include <nuttx/arch.h>
#include <arch/irq.h>
#include "up_vfork.h"
#include "os_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* ARM requires at least a 4-byte stack alignment. For use with EABI and
* floating point, the stack must be aligned to 8-byte addresses.
*/
#ifndef CONFIG_STACK_ALIGNMENT
/* The symbol __ARM_EABI__ is defined by GCC if EABI is being used. If you
* are not using GCC, make sure that CONFIG_STACK_ALIGNMENT is set correctly!
*/
# ifdef __ARM_EABI__
# define CONFIG_STACK_ALIGNMENT 8
# else
# define CONFIG_STACK_ALIGNMENT 4
# endif
#endif
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: up_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.
*
* 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.
*
* task_vforkabort() may be called if an error occurs between steps 3 and 6.
*
* Input Paremeters:
* context - Caller context information saved by vfork()
*
* 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.
*
****************************************************************************/
pid_t up_vfork(const struct vfork_s *context)
{
_TCB *parent = (FAR _TCB *)g_readytorun.head;
_TCB *child;
size_t stacksize;
uint32_t newsp;
uint32_t newfp;
uint32_t stackutil;
int ret;
svdbg("r4:%08x r5:%08x r6:%08x r7:%08x\n",
context->r4, context->r5, context->r6, context->r7);
svdbg("r8:%08x r9:%08x r10:%08x\n",
context->r8, context->r9, context->r10);
svdbg("fp:%08x sp:%08x lr:%08x\n",
context->fp, context->sp, context->lr);
/* Allocate and initialize a TCB for the child task. */
child = task_vforksetup((start_t)(context->lr & ~1));
if (!child)
{
sdbg("task_vforksetup failed\n");
return (pid_t)ERROR;
}
svdbg("Parent=%p Child=%p\n", parent, child);
/* Get the size of the parent task's stack. Due to alignment operations,
* the adjusted stack size may be smaller than the stack size originally
* requrested.
*/
stacksize = parent->adj_stack_size + CONFIG_STACK_ALIGNMENT - 1;
/* Allocate the stack for the TCB */
ret = up_create_stack(child, stacksize);
if (ret != OK)
{
sdbg("up_create_stack failed: %d\n", ret);
task_vforkabort(child, -ret);
return (pid_t)ERROR;
}
/* How much of the parent's stack was utilized? The ARM uses
* a push-down stack so that the current stack pointer should
* be lower than the initial, adjusted stack pointer. The
* stack usage should be the difference between those two.
*/
DEBUGASSERT((uint32_t)parent->adj_stack_ptr > context->sp);
stackutil = (uint32_t)parent->adj_stack_ptr - context->sp;
svdbg("stacksize:%d stackutil:%d\n", stacksize, stackutil);
/* Make some feeble effort to perserve the stack contents. This is
* feeble because the stack surely contains invalid pointers and other
* content that will not work in the child context. However, if the
* user follows all of the caveats of vfor() usage, even this feeble
* effort is overkill.
*/
newsp = (uint32_t)child->adj_stack_ptr - stackutil;
memcpy((void *)newsp, (const void *)context->sp, stackutil);
/* Was there a frame pointer in place before? */
if (context->fp <= (uint32_t)parent->adj_stack_ptr &&
context->fp >= (uint32_t)parent->adj_stack_ptr - stacksize)
{
uint32_t frameutil = (uint32_t)parent->adj_stack_ptr - context->fp;
newfp = (uint32_t)child->adj_stack_ptr - frameutil;
}
else
{
newfp = context->fp;
}
svdbg("Old stack base:%08x SP:%08x FP:%08x\n",
parent->adj_stack_ptr, context->sp, context->fp);
svdbg("New stack base:%08x SP:%08x FP:%08x\n",
child->adj_stack_ptr, newsp, newfp);
/* Update the stack pointer, frame pointer, and volatile registers. When
* the child TCB was initialized, all of the values were set to zero.
* up_initial_state() altered a few values, but the return value in R0
* should be cleared to zero, providing the indication to the newly started
* child thread.
*/
child->xcp.regs[REG_R4] = context->r4; /* Volatile register r4 */
child->xcp.regs[REG_R5] = context->r5; /* Volatile register r5 */
child->xcp.regs[REG_R6] = context->r6; /* Volatile register r6 */
child->xcp.regs[REG_R7] = context->r7; /* Volatile register r7 */
child->xcp.regs[REG_R8] = context->r8; /* Volatile register r8 */
child->xcp.regs[REG_R9] = context->r9; /* Volatile register r9 */
child->xcp.regs[REG_R10] = context->r10; /* Volatile register r10 */
child->xcp.regs[REG_FP] = newfp; /* Frame pointer */
child->xcp.regs[REG_SP] = newsp; /* Stack pointer */
/* And, finally, start the child task. On a failure, task_vforkstart()
* will discard the TCB by calling task_vforkabort().
*/
return task_vforkstart(child);
}
