/***********************************************************************/
/*                                                                     */
/*                                OCaml                                */
/*                                                                     */
/*            Xavier Leroy, projet Gallium, INRIA Rocquencourt         */
/*                                                                     */
/*  Copyright 2006 Institut National de Recherche en Informatique et   */
/*  en Automatique.  All rights reserved.  This file is distributed    */
/*  under the terms of the GNU Library General Public License, with    */
/*  the special exception on linking described in file ../LICENSE.     */
/*                                                                     */
/***********************************************************************/

/* Stack backtrace for uncaught exceptions */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "alloc.h"
#include "backtrace.h"
#include "memory.h"
#include "misc.h"
#include "mlvalues.h"
#include "stack.h"

int caml_backtrace_active = 0;
int caml_backtrace_pos = 0;
code_t * caml_backtrace_buffer = NULL;
value caml_backtrace_last_exn = Val_unit;
#define BACKTRACE_BUFFER_SIZE 1024

/* Start or stop the backtrace machinery */

CAMLprim value caml_record_backtrace(value vflag)
{
  int flag = Int_val(vflag);

  if (flag != caml_backtrace_active) {
    caml_backtrace_active = flag;
    caml_backtrace_pos = 0;
    if (flag) {
      caml_register_global_root(&caml_backtrace_last_exn);
    } else {
      caml_remove_global_root(&caml_backtrace_last_exn);
    }
  }
  return Val_unit;
}

/* Return the status of the backtrace machinery */

CAMLprim value caml_backtrace_status(value vunit)
{
  return Val_bool(caml_backtrace_active);
}

/* Store the return addresses contained in the given stack fragment
   into the backtrace array */

void caml_stash_backtrace(value exn, uintnat pc, char * sp, char * trapsp)
{
  frame_descr * d;
  uintnat h;

  if (exn != caml_backtrace_last_exn) {
    caml_backtrace_pos = 0;
    caml_backtrace_last_exn = exn;
  }
  if (caml_backtrace_buffer == NULL) {
    caml_backtrace_buffer = malloc(BACKTRACE_BUFFER_SIZE * sizeof(code_t));
    if (caml_backtrace_buffer == NULL) return;
  }
  if (caml_frame_descriptors == NULL) caml_init_frame_descriptors();

  while (1) {
    /* Find the descriptor corresponding to the return address */
    h = Hash_retaddr(pc);
    while(1) {
      d = caml_frame_descriptors[h];
      if (d == 0) return; /* can happen if some code not compiled with -g */
      if (d->retaddr == pc) break;
      h = (h+1) & caml_frame_descriptors_mask;
    }
    /* Skip to next frame */
    if (d->frame_size != 0xFFFF) {
      /* Regular frame, store its descriptor in the backtrace buffer */
      if (caml_backtrace_pos >= BACKTRACE_BUFFER_SIZE) return;
      caml_backtrace_buffer[caml_backtrace_pos++] = (code_t) d;
#ifndef Stack_grows_upwards
      sp += (d->frame_size & 0xFFFC);
#else
      sp -= (d->frame_size & 0xFFFC);
#endif
      pc = Saved_return_address(sp);
#ifdef Mask_already_scanned
      pc = Mask_already_scanned(pc);
#endif
    } else {
      /* Special frame marking the top of a stack chunk for an ML callback.
         Skip C portion of stack and continue with next ML stack chunk. */
      struct caml_context * next_context = Callback_link(sp);
      sp = next_context->bottom_of_stack;
      pc = next_context->last_retaddr;
      /* A null sp means no more ML stack chunks; stop here. */
      if (sp == NULL) return;
    }
    /* Stop when we reach the current exception handler */
#ifndef Stack_grows_upwards
    if (sp > trapsp) return;
#else
    if (sp < trapsp) return;
#endif
  }
}

/* Extract location information for the given frame descriptor */

struct loc_info {
  int loc_valid;
  int loc_is_raise;
  char * loc_filename;
  int loc_lnum;
  int loc_startchr;
  int loc_endchr;
};

static void extract_location_info(frame_descr * d,
                                  /*out*/ struct loc_info * li)
{
  uintnat infoptr;
  uint32 info1, info2;

  /* If no debugging information available, print nothing.
     When everything is compiled with -g, this corresponds to
     compiler-inserted re-raise operations. */
  if ((d->frame_size & 1) == 0) {
    li->loc_valid = 0;
    li->loc_is_raise = 1;
    return;
  }
  /* Recover debugging info */
  infoptr = ((uintnat) d +
             sizeof(char *) + sizeof(short) + sizeof(short) +
             sizeof(short) * d->num_live + sizeof(frame_descr *) - 1)
            & -sizeof(frame_descr *);
  info1 = ((uint32 *)infoptr)[0];
  info2 = ((uint32 *)infoptr)[1];
  /* Format of the two info words:
       llllllllllllllllllll aaaaaaaa bbbbbbbbbb nnnnnnnnnnnnnnnnnnnnnnnn kk
                          44       36         26                       2  0
                       (32+12)    (32+4)
     k ( 2 bits): 0 if it's a call, 1 if it's a raise
     n (24 bits): offset (in 4-byte words) of file name relative to infoptr
     l (20 bits): line number
     a ( 8 bits): beginning of character range
     b (10 bits): end of character range */
  li->loc_valid = 1;
  li->loc_is_raise = (info1 & 3) != 0;
  li->loc_filename = (char *) infoptr + (info1 & 0x3FFFFFC);
  li->loc_lnum = info2 >> 12;
  li->loc_startchr = (info2 >> 4) & 0xFF;
  li->loc_endchr = ((info2 & 0xF) << 6) | (info1 >> 26);
}

static void print_location(struct loc_info * li, int index)
{
  char * info;

  /* Ignore compiler-inserted raise */
  if (!li->loc_valid) return;

  if (index == 0)
    info = "Raised at";
  else if (li->loc_is_raise)
    info = "Re-raised at";
  else
    info = "Called from";
  fprintf (stderr, "%s file \"%s\", line %d, characters %d-%d\n",
           info, li->loc_filename, li->loc_lnum,
           li->loc_startchr, li->loc_endchr);
}

/* Print a backtrace */

void caml_print_exception_backtrace(void)
{
  int i;
  struct loc_info li;

  for (i = 0; i < caml_backtrace_pos; i++) {
    extract_location_info((frame_descr *) (caml_backtrace_buffer[i]), &li);
    print_location(&li, i);
  }
}

/* Convert the raw backtrace to a data structure usable from OCaml */

CAMLprim value caml_convert_raw_backtrace(value backtrace) {
  CAMLparam1(backtrace);
  CAMLlocal4(res, arr, p, fname);
  int i;
  struct loc_info li;

  arr = caml_alloc(Wosize_val(backtrace), 0);
  for (i = 0; i < Wosize_val(backtrace); i++) {
    extract_location_info((frame_descr *) Field(backtrace, i), &li);
    if (li.loc_valid) {
      fname = caml_copy_string(li.loc_filename);
      p = caml_alloc_small(5, 0);
      Field(p, 0) = Val_bool(li.loc_is_raise);
      Field(p, 1) = fname;
      Field(p, 2) = Val_int(li.loc_lnum);
      Field(p, 3) = Val_int(li.loc_startchr);
      Field(p, 4) = Val_int(li.loc_endchr);
    } else {
      p = caml_alloc_small(1, 1);
      Field(p, 0) = Val_bool(li.loc_is_raise);
    }
    caml_modify(&Field(arr, i), p);
  }
  res = caml_alloc_small(1, 0); Field(res, 0) = arr; /* Some */
  CAMLreturn(res);
}

/* Get a copy of the latest backtrace */

CAMLprim value caml_get_exception_raw_backtrace(value unit)
{
  CAMLparam0();
  CAMLlocal1(res);
  res = caml_alloc(caml_backtrace_pos, Abstract_tag);
  if(caml_backtrace_buffer != NULL)
    memcpy(&Field(res, 0), caml_backtrace_buffer,
           caml_backtrace_pos * sizeof(code_t));
  CAMLreturn(res);
}

/* the function below is deprecated: we previously returned directly
   the OCaml-usable representation, instead of the raw backtrace as an
   abstract type, but this has a large performance overhead if you
   store a lot of backtraces and print only some of them.

   It is not used by the Printexc library anymore, or anywhere else in
   the compiler, but we have kept it in case some user still depends
   on it as an external.
*/

CAMLprim value caml_get_exception_backtrace(value unit)
{
  CAMLparam0();
  CAMLlocal2(raw,res);
  raw = caml_get_exception_raw_backtrace(unit);
  res = caml_convert_raw_backtrace(raw);
  CAMLreturn(res);
}