text: /****************************************************************************
   * arch/arm/src/common/arm_vfork.c
   *
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.  The
   * ASF licenses this file to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance with the
   * License.  You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
   * License for the specific language governing permissions and limitations
   * under the License.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * 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 "arm_vfork.h"
  #include "sched/sched.h"
  
  /****************************************************************************
   * Pre-processor Definitions
   ****************************************************************************/
  
  /* For use with EABI and floating point, the stack must be aligned to 8-byte
   * addresses.
   */
  
  #define CONFIG_STACK_ALIGNMENT 8
  
  /****************************************************************************
   * 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 nxtask_setup_vfork().
   *   3) nxtask_setup_vfork() 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 input 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 nxtask_start_vfork()
   *   6) nxtask_start_vfork() then executes the child thread.
   *
   * nxtask_abort_vfork() may be called if an error occurs between steps 3 and
   * 6.
   *
   * Input Parameters:
   *   context - Caller context information saved by vfork()
   *
   * Returned Value:
   *   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)
  {
    struct tcb_s *parent = this_task();
    struct task_tcb_s *child;
    size_t stacksize;
    uint32_t newsp;
    uint32_t newfp;
    uint32_t stackutil;
    size_t argsize;
    void *argv;
    int ret;
  
    sinfo("vfork context [%p]:\n", context);
    sinfo("  r4:%08x r5:%08x r6:%08x r7:%08x\n",
          context->r4, context->r5, context->r6, context->r7);
    sinfo("  r8:%08x r9:%08x r10:%08x\n",
          context->r8, context->r9, context->r10);
    sinfo("  fp:%08x sp:%08x lr:%08x\n",
          context->fp, context->sp, context->lr);
  
    /* Allocate and initialize a TCB for the child task. */
  
    child = nxtask_setup_vfork((start_t)(context->lr & ~1), &argsize);
    if (!child)
      {
        serr("ERROR: nxtask_setup_vfork failed\n");
        return (pid_t)ERROR;
      }
  
    sinfo("TCBs: Parent=%p Child=%p\n", parent, child);
  
    /* Get the size of the parent task's stack. */
  
    stacksize = parent->adj_stack_size;
  
    /* Allocate the stack for the TCB */
  
    ret = up_create_stack((FAR struct tcb_s *)child, stacksize + argsize,
                          parent->flags & TCB_FLAG_TTYPE_MASK);
    if (ret != OK)
      {
        serr("ERROR: up_create_stack failed: %d\n", ret);
        nxtask_abort_vfork(child, -ret);
        return (pid_t)ERROR;
      }
  
    /* Allocate the memory and copy argument from parent task */
  
    argv = up_stack_frame((FAR struct tcb_s *)child, argsize);
    memcpy(argv, parent->adj_stack_ptr, argsize);
  
    /* 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;
  
    sinfo("Parent: stacksize:%d stackutil:%d\n", stacksize, stackutil);
  
    /* Make some feeble effort to preserve 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 vfork() usage, even this feeble
     * effort is overkill.
     */
  
    newsp = (uint32_t)child->cmn.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->cmn.adj_stack_ptr - frameutil;
      }
    else
      {
        newfp = context->fp;
      }
  
    sinfo("Parent: stack base:%08x SP:%08x FP:%08x\n",
          parent->adj_stack_ptr, context->sp, context->fp);
    sinfo("Child:  stack base:%08x SP:%08x FP:%08x\n",
          child->cmn.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->cmn.xcp.regs[REG_R4]  = context->r4;  /* Volatile register r4 */
    child->cmn.xcp.regs[REG_R5]  = context->r5;  /* Volatile register r5 */
    child->cmn.xcp.regs[REG_R6]  = context->r6;  /* Volatile register r6 */
    child->cmn.xcp.regs[REG_R7]  = context->r7;  /* Volatile register r7 */
    child->cmn.xcp.regs[REG_R8]  = context->r8;  /* Volatile register r8 */
    child->cmn.xcp.regs[REG_R9]  = context->r9;  /* Volatile register r9 */
    child->cmn.xcp.regs[REG_R10] = context->r10; /* Volatile register r10 */
    child->cmn.xcp.regs[REG_FP]  = newfp;        /* Frame pointer */
    child->cmn.xcp.regs[REG_SP]  = newsp;        /* Stack pointer */
  
  #ifdef CONFIG_LIB_SYSCALL
    /* If we got here via a syscall, then we are going to have to setup some
     * syscall return information as well.
     */
  
    if (parent->xcp.nsyscalls > 0)
      {
        int index;
        for (index = 0; index < parent->xcp.nsyscalls; index++)
          {
            child->cmn.xcp.syscall[index].sysreturn =
              parent->xcp.syscall[index].sysreturn;
  
            /* REVISIT:  This logic is *not* common. */
  
  #if defined(CONFIG_ARCH_ARMV7A)
  #  ifdef CONFIG_BUILD_KERNEL
  
            child->cmn.xcp.syscall[index].cpsr =
              parent->xcp.syscall[index].cpsr;
  
  #  endif
  
  #elif defined(CONFIG_ARCH_ARMV7R)
  #  ifdef CONFIG_BUILD_PROTECTED
  
            child->cmn.xcp.syscall[index].cpsr =
              parent->xcp.syscall[index].cpsr;
  
  #  endif
  #elif defined(CONFIG_ARCH_ARMV6M) || defined(CONFIG_ARCH_ARMV7M) || \
        defined(CONFIG_ARCH_ARMV8M)
  
            child->cmn.xcp.syscall[index].excreturn =
              parent->xcp.syscall[index].excreturn;
  #else
  #  error Missing logic
  #endif
          }
  
        child->cmn.xcp.nsyscalls = parent->xcp.nsyscalls;
      }
  #endif
  
    /* And, finally, start the child task.  On a failure, nxtask_start_vfork()
     * will discard the TCB by calling nxtask_abort_vfork().
     */
  
    return nxtask_start_vfork(child);
  }
  