factor/vm/cpu-x86.cpp

#include "master.hpp"

namespace factor {

void factor_vm::dispatch_non_resumable_signal(cell* sp, cell* pc,
                                              cell handler,
                                              cell limit) {

  /* Fault came from the VM or foreign code. We don't try to fix the
     call stack from *sp and instead use the last saved "good value"
     which we get from ctx->callstack_top. Then launch the handler
     without going through the resumable subprimitive. */
  signal_resumable = false;

  cell frame_top = ctx->callstack_top;

  if (frame_top < ctx->callstack_seg->start) {
    /* The saved callstack pointer is outside the callstack
       segment. That means that we need to carefully cut off one frame
       first which hopefully should put the pointer within the
       callstack's bounds. */
    code_block *block = code->code_block_for_address(*pc);
    cell frame_size = block->stack_frame_size_for_address(*pc);
    frame_top += frame_size;
  }

  /* Cut the callstack down to the shallowest Factor stack
     frame that leaves room for the signal handler to do its thing,
     and launch the handler without going through the resumable
     subprimitive. */
  FACTOR_ASSERT(ctx->callstack_seg->start <= frame_top);
  while (frame_top < ctx->callstack_bottom && frame_top < limit) {
    frame_top = code->frame_predecessor(frame_top);
  }
  ctx->callstack_top = frame_top;
  *sp = frame_top;
  *pc = handler;
}

void factor_vm::dispatch_resumable_signal(cell* sp, cell* pc, cell handler) {

  signal_resumable = true;

  /* Fault came from Factor, and we've got a good callstack. Route the
     signal handler through the resumable signal handler
     subprimitive. */

  cell offset = *sp % 16;

  signal_handler_addr = handler;

  /* True stack frames are always 16-byte aligned. Leaf procedures
     that don't create a stack frame will be out of alignment by
     sizeof(cell) bytes. */
  /* On architectures with a link register we would have to check for
     leafness by matching the PC to a word. We should also use
     FRAME_RETURN_ADDRESS instead of assuming the stack pointer is the
     right place to put the resume address. */
  cell word_idx = 0;
  if (offset == 0) {
    word_idx = SIGNAL_HANDLER_WORD;

    cell newsp = *sp - sizeof(cell);
    *sp = newsp;
    *(cell*)newsp = *pc;

  } else if (offset == 16 - sizeof(cell)) {
    word_idx = LEAF_SIGNAL_HANDLER_WORD;
    /* Make a fake frame for the leaf procedure */
    FACTOR_ASSERT(code->code_block_for_address(*pc) != NULL);

    cell newsp = *sp - LEAF_FRAME_SIZE;
    *sp = newsp;
    *(cell*)newsp = *pc;

  } else {
    FACTOR_ASSERT(false);
  }
  tagged<word> handler_word = tagged<word>(special_objects[word_idx]);
  *pc = (cell)handler_word->entry_point;
}

void factor_vm::dispatch_signal_handler(cell* sp, cell* pc, cell handler) {

  bool in_code_seg = code->seg->in_segment_p(*pc);
  cell cs_limit = ctx->callstack_seg->start + stack_reserved;
  bool resumable_p = in_code_seg && *sp >= cs_limit;
  if (resumable_p) {
    dispatch_resumable_signal(sp, pc, handler);
  } else {
    dispatch_non_resumable_signal(sp, pc, handler, cs_limit);
  }

  /* Poking with the stack pointer, which the above code does, means
     that pointers to stack-allocated objects will become
     corrupted. Therefore the root vectors needs to be cleared because
     their pointers to stack variables are now garbage. */
  data_roots.clear();
  code_roots.clear();
}

}