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backtrace.c
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backtrace.c
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/***********************************************************************/
/* */
/* 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. */
/* */
/***********************************************************************/
/* $Id$ */
/* Stack backtrace for uncaught exceptions */
#include <stdio.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 backtrace to a data structure usable from OCaml */
CAMLprim value caml_get_exception_backtrace(value unit)
{
CAMLparam0();
CAMLlocal4(res, arr, p, fname);
int i;
struct loc_info li;
arr = caml_alloc(caml_backtrace_pos, 0);
for (i = 0; i < caml_backtrace_pos; i++) {
extract_location_info((frame_descr *) (caml_backtrace_buffer[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);
}