path: root/dwarflint/readctx.cc

/* Pedantic checking of DWARF files.
   Copyright (C) 2009, 2010 Red Hat, Inc.
   This file is part of Red Hat elfutils.
   Written by Petr Machata <pmachata@redhat.com>, 2009.

   Red Hat elfutils is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by the
   Free Software Foundation; version 2 of the License.

   Red Hat elfutils is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License along
   with Red Hat elfutils; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA.

   Red Hat elfutils is an included package of the Open Invention Network.
   An included package of the Open Invention Network is a package for which
   Open Invention Network licensees cross-license their patents.  No patent
   license is granted, either expressly or impliedly, by designation as an
   included package.  Should you wish to participate in the Open Invention
   Network licensing program, please visit www.openinventionnetwork.com
   <http://www.openinventionnetwork.com>.  */

#include "readctx.hh"
#include "../libdw/dwarf.h"

#include <stdlib.h>
#include <assert.h>
#include <byteswap.h>
#include <inttypes.h>

/* read_Xubyte_* is basically cut'n'paste from memory-access.h.  */
union unaligned
  {
    void *p;
    uint16_t u2;
    uint32_t u4;
    uint64_t u8;
    int16_t s2;
    int32_t s4;
    int64_t s8;
  } __attribute__ ((packed));

static uint16_t
read_2ubyte_unaligned (const void *p, bool other_byte_order)
{
  const union unaligned *up = (const union unaligned *)p;
  if (other_byte_order)
    return bswap_16 (up->u2);
  return up->u2;
}

/* Prefix with dwarflint_ for export, so that it doesn't get confused
   with functions and macros in memory-access.h.  */
uint32_t
dwarflint_read_4ubyte_unaligned (const void *p, bool other_byte_order)
{
  const union unaligned *up = (const union unaligned *)p;
  if (other_byte_order)
    return bswap_32 (up->u4);
  return up->u4;
}

uint64_t
dwarflint_read_8ubyte_unaligned (const void *p, bool other_byte_order)
{
  const union unaligned *up = (const union unaligned *)p;
  if (other_byte_order)
    return bswap_64 (up->u8);
  return up->u8;
}


#define read_2ubyte_unaligned_inc(Addr, OtherByteOrder)			\
  ({ uint16_t t_ = read_2ubyte_unaligned (Addr, OtherByteOrder);	\
    Addr = (__typeof (Addr)) (((uintptr_t) (Addr)) + 2);		\
    t_; })

#define read_4ubyte_unaligned_inc(Addr, OtherByteOrder)			\
  ({ uint32_t t_ = dwarflint_read_4ubyte_unaligned (Addr, OtherByteOrder); \
    Addr = (__typeof (Addr)) (((uintptr_t) (Addr)) + 4);		\
    t_; })

#define read_8ubyte_unaligned_inc(Addr, OtherByteOrder)			\
  ({ uint64_t t_ = dwarflint_read_8ubyte_unaligned (Addr, OtherByteOrder); \
    Addr = (__typeof (Addr)) (((uintptr_t) (Addr)) + 8);		\
    t_; })



void
read_ctx_init (struct read_ctx *ctx, Elf_Data *data, bool other_byte_order)
{
  if (data == NULL)
    abort ();

  ctx->data = data;
  ctx->begin = (const unsigned char *)data->d_buf;
  ctx->end = (const unsigned char *)data->d_buf + data->d_size;
  ctx->ptr = (const unsigned char *)data->d_buf;
  ctx->other_byte_order = other_byte_order;
}

bool
read_ctx_init_sub (struct read_ctx *ctx, struct read_ctx *parent,
		   const unsigned char *begin, const unsigned char *end)
{
  if (parent == NULL)
    abort ();

  if (begin < parent->begin
      || end > parent->end)
    return false;

  ctx->data = parent->data;
  ctx->begin = begin;
  ctx->end = end;
  ctx->ptr = begin;
  ctx->other_byte_order = parent->other_byte_order;
  return true;
}

uint64_t
read_ctx_get_offset (struct read_ctx *ctx)
{
  assert (ctx->ptr >= ctx->begin);
  return (uint64_t)(ctx->ptr - ctx->begin);
}

bool
read_ctx_need_data (struct read_ctx *ctx, size_t length)
{
  const unsigned char *ptr = ctx->ptr + length;
  return ptr <= ctx->end && (length == 0 || ptr > ctx->ptr);
}

bool
read_ctx_read_ubyte (struct read_ctx *ctx, unsigned char *ret)
{
  if (!read_ctx_need_data (ctx, 1))
    return false;
  if (ret != NULL)
    *ret = *ctx->ptr;
  ctx->ptr++;
  return true;
}

int
read_ctx_read_uleb128 (struct read_ctx *ctx, uint64_t *ret)
{
  uint64_t result = 0;
  int shift = 0;
  int size = 8 * sizeof (result);
  bool zero_tail = false;

  while (1)
    {
      uint8_t byte;
      if (!read_ctx_read_ubyte (ctx, &byte))
	return -1;

      uint8_t payload = byte & 0x7f;
      zero_tail = payload == 0 && shift > 0;
      result |= (uint64_t)payload << shift;
      shift += 7;
      if (shift > size && byte != 0x1)
	return -1;
      if ((byte & 0x80) == 0)
	break;
    }

  if (ret != NULL)
    *ret = result;
  return zero_tail ? 1 : 0;
}

int
read_ctx_read_sleb128 (struct read_ctx *ctx, int64_t *ret)
{
  int64_t result = 0;
  int shift = 0;
  int size = 8 * sizeof (result);
  bool zero_tail = false;
  bool sign = false;

  while (1)
    {
      uint8_t byte;
      if (!read_ctx_read_ubyte (ctx, &byte))
	return -1;

      uint8_t payload = byte & 0x7f;
      zero_tail = shift > 0 && ((payload == 0x7f && sign)
				|| (payload == 0 && !sign));
      sign = (byte & 0x40) != 0; /* Set sign for rest of loop & next round.  */
      result |= (int64_t)payload << shift;
      shift += 7;
      if ((byte & 0x80) == 0)
	{
	  if (shift < size && sign)
	    result |= -((int64_t)1 << shift);
	  break;
	}
      if (shift > size)
	return -1;
    }

  if (ret != NULL)
    *ret = result;
  return zero_tail ? 1 : 0;
}

bool
read_ctx_read_2ubyte (struct read_ctx *ctx, uint16_t *ret)
{
  if (!read_ctx_need_data (ctx, 2))
    return false;
  uint16_t val = read_2ubyte_unaligned_inc (ctx->ptr, ctx->other_byte_order);
  if (ret != NULL)
    *ret = val;
  return true;
}

bool
read_ctx_read_4ubyte (struct read_ctx *ctx, uint32_t *ret)
{
  if (!read_ctx_need_data (ctx, 4))
    return false;
  uint32_t val = read_4ubyte_unaligned_inc (ctx->ptr, ctx->other_byte_order);
  if (ret != NULL)
    *ret = val;
  return true;
}

bool
read_ctx_read_8ubyte (struct read_ctx *ctx, uint64_t *ret)
{
  if (!read_ctx_need_data (ctx, 8))
    return false;
  uint64_t val = read_8ubyte_unaligned_inc (ctx->ptr, ctx->other_byte_order);
  if (ret != NULL)
    *ret = val;
  return true;
}

bool
read_ctx_read_offset (struct read_ctx *ctx, bool dwarf64, uint64_t *ret)
{
  if (dwarf64)
    return read_ctx_read_8ubyte (ctx, ret);

  uint32_t v;
  if (!read_ctx_read_4ubyte (ctx, &v))
    return false;

  if (ret != NULL)
    *ret = (uint64_t)v;
  return true;
}

bool
read_ctx_read_var (struct read_ctx *ctx, int width, uint64_t *ret)
{
  switch (width)
    {
    case 4:
    case 8:
      return read_ctx_read_offset (ctx, width == 8, ret);
    case 2:
      {
	uint16_t val;
	if (!read_ctx_read_2ubyte (ctx, &val))
	  return false;
	*ret = val;
	return true;
      }
    case 1:
      {
	uint8_t val;
	if (!read_ctx_read_ubyte (ctx, &val))
	  return false;
	*ret = val;
	return true;
      }
    default:
      return false;
    };
}

const char *
read_ctx_read_str (struct read_ctx *ctx)
{
  const char *ret = (const char *)ctx->ptr;
  uint8_t byte;
  do
    if (!read_ctx_read_ubyte (ctx, &byte))
      return NULL;
  while (byte != 0);
  return ret;
}

bool
read_ctx_skip (struct read_ctx *ctx, uint64_t len)
{
  if (!read_ctx_need_data (ctx, len))
    return false;
  ctx->ptr += len;
  return true;
}

bool
read_ctx_eof (struct read_ctx *ctx)
{
  return !read_ctx_need_data (ctx, 1);
}

static void
update_off (struct read_ctx *ctx,
	    uint64_t *ret_off)
{
  if (ret_off != NULL)
    *ret_off = (uint64_t)(ctx->ptr - ctx->begin);
}

bool
read_check_zero_padding (struct read_ctx *ctx,
			 uint64_t *ret_off_start,
			 uint64_t *ret_off_end)
{
  assert (ctx->ptr != ctx->end);
  update_off (ctx, ret_off_start);
  bool ret = true;

  const unsigned char *save_ptr = ctx->ptr;
  while (!read_ctx_eof (ctx))
    if (*ctx->ptr++ != 0)
      {
	ctx->ptr = save_ptr;
	goto done;
      }

 done:
  update_off (ctx, ret_off_end);
  return ret;
}