Function arm_fork

arch/arm/src/common/arm_fork.c:92–245

 ****************************************************************************/

pid_t arm_fork(const struct fork_s *context)
{
  struct tcb_s *parent = this_task();
  struct tcb_s *child;
  uint32_t newsp;
  uint32_t newfp;
  uint32_t newtop;
  uint32_t stacktop;
  uint32_t stackutil;
#ifdef CONFIG_ARCH_KERNEL_STACK
  uint32_t oldsp = (uint32_t)parent->xcp.ustkptr;
#else
  uint32_t oldsp = context->sp;
#endif

  sinfo("fork context [%p]:\n", context);
  sinfo("  r4:%08" PRIx32 " r5:%08" PRIx32
        " r6:%08" PRIx32 " r7:%08" PRIx32 "\n",
        context->r4, context->r5, context->r6, context->r7);
  sinfo("  r8:%08" PRIx32 " r9:%08" PRIx32 " r10:%08" PRIx32 "\n",
        context->r8, context->r9, context->r10);
  sinfo("  r11:%08" PRIx32 " sp:%08" PRIx32 " lr:%08" PRIx32 "\n",
        context->r11, oldsp, context->lr);

  /* Allocate and initialize a TCB for the child task. */

  child = nxtask_setup_fork((start_t)(context->lr & ~1));
  if (!child)
    {
      serr("ERROR: nxtask_setup_fork failed\n");
      return (pid_t)ERROR;
    }

  sinfo("TCBs: Parent=%p Child=%p\n", parent, child);

  /* 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.
   */

  stacktop = (uint32_t)parent->stack_base_ptr +
                       parent->adj_stack_size;
  DEBUGASSERT(stacktop > oldsp && oldsp >= (uint32_t)parent->stack_base_ptr);
  stackutil = stacktop - oldsp;

  sinfo("Parent: stackutil:%" PRIu32 "\n", 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 fork() usage, even this feeble
   * effort is overkill.
   */

  newtop = (uint32_t)child->stack_base_ptr +
                     child->adj_stack_size;