Merge pull request #2581 from 4144/backtrace

Add proper backtrace logging even if functions is hidden.

1 files changed, 3126 insertions, 0 deletions

diff --git a/3rdparty/libbacktrace/dwarf.c b/3rdparty/libbacktrace/dwarf.c
new file mode 100644
index 000000000..c378b2517
--- /dev/null
+++ b/3rdparty/libbacktrace/dwarf.c
@@ -0,0 +1,3126 @@
+/* dwarf.c -- Get file/line information from DWARF for backtraces.
+   Copyright (C) 2012-2018 Free Software Foundation, Inc.
+   Written by Ian Lance Taylor, Google.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    (1) Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+
+    (2) Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in
+    the documentation and/or other materials provided with the
+    distribution.
+
+    (3) The name of the author may not be used to
+    endorse or promote products derived from this software without
+    specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.  */
+
+#include "config.h"
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+
+#include "backtrace.h"
+#include "internal.h"
+
+/* DWARF constants.  */
+
+enum dwarf_tag {
+  DW_TAG_entry_point = 0x3,
+  DW_TAG_compile_unit = 0x11,
+  DW_TAG_inlined_subroutine = 0x1d,
+  DW_TAG_subprogram = 0x2e,
+};
+
+enum dwarf_form {
+  DW_FORM_addr = 0x1,
+  DW_FORM_block2 = 0x3,
+  DW_FORM_block4 = 0x4,
+  DW_FORM_data2 = 0x5,
+  DW_FORM_data4 = 0x6,
+  DW_FORM_data8 = 0x07,
+  DW_FORM_string = 0x08,
+  DW_FORM_block = 0x09,
+  DW_FORM_block1 = 0x0a,
+  DW_FORM_data1 = 0x0b,
+  DW_FORM_flag = 0x0c,
+  DW_FORM_sdata = 0x0d,
+  DW_FORM_strp = 0x0e,
+  DW_FORM_udata = 0x0f,
+  DW_FORM_ref_addr = 0x10,
+  DW_FORM_ref1 = 0x11,
+  DW_FORM_ref2 = 0x12,
+  DW_FORM_ref4 = 0x13,
+  DW_FORM_ref8 = 0x14,
+  DW_FORM_ref_udata = 0x15,
+  DW_FORM_indirect = 0x16,
+  DW_FORM_sec_offset = 0x17,
+  DW_FORM_exprloc = 0x18,
+  DW_FORM_flag_present = 0x19,
+  DW_FORM_ref_sig8 = 0x20,
+  DW_FORM_GNU_addr_index = 0x1f01,
+  DW_FORM_GNU_str_index = 0x1f02,
+  DW_FORM_GNU_ref_alt = 0x1f20,
+  DW_FORM_GNU_strp_alt = 0x1f21,
+};
+
+enum dwarf_attribute {
+  DW_AT_name = 0x3,
+  DW_AT_stmt_list = 0x10,
+  DW_AT_low_pc = 0x11,
+  DW_AT_high_pc = 0x12,
+  DW_AT_comp_dir = 0x1b,
+  DW_AT_abstract_origin = 0x31,
+  DW_AT_specification = 0x47,
+  DW_AT_ranges = 0x55,
+  DW_AT_call_file = 0x58,
+  DW_AT_call_line = 0x59,
+  DW_AT_linkage_name = 0x6e,
+  DW_AT_MIPS_linkage_name = 0x2007,
+};
+
+enum dwarf_line_number_op {
+  DW_LNS_extended_op = 0x0,
+  DW_LNS_copy = 0x1,
+  DW_LNS_advance_pc = 0x2,
+  DW_LNS_advance_line = 0x3,
+  DW_LNS_set_file = 0x4,
+  DW_LNS_set_column = 0x5,
+  DW_LNS_negate_stmt = 0x6,
+  DW_LNS_set_basic_block = 0x7,
+  DW_LNS_const_add_pc = 0x8,
+  DW_LNS_fixed_advance_pc = 0x9,
+  DW_LNS_set_prologue_end = 0xa,
+  DW_LNS_set_epilogue_begin = 0xb,
+  DW_LNS_set_isa = 0xc,
+};
+
+enum dwarf_extedned_line_number_op {
+  DW_LNE_end_sequence = 0x1,
+  DW_LNE_set_address = 0x2,
+  DW_LNE_define_file = 0x3,
+  DW_LNE_set_discriminator = 0x4,
+};
+
+#if defined(__MSDOS__) || defined(_WIN32) || defined(__OS2__) || defined (__CYGWIN__)
+# define IS_DIR_SEPARATOR(c) ((c) == '/' || (c) == '\\')
+#define HAS_DRIVE_SPEC(f) ((f)[0] && (f)[1] == ':')
+# define IS_ABSOLUTE_PATH(f) (IS_DIR_SEPARATOR(f[0]) || HAS_DRIVE_SPEC(f))
+#else
+# define IS_DIR_SEPARATOR(c) ((c) == '/')
+# define IS_ABSOLUTE_PATH(f) IS_DIR_SEPARATOR(f[0])
+#endif
+
+#if !defined(HAVE_DECL_STRNLEN) || !HAVE_DECL_STRNLEN
+
+/* If strnlen is not declared, provide our own version.  */
+
+static size_t
+xstrnlen (const char *s, size_t maxlen)
+{
+  size_t i;
+
+  for (i = 0; i < maxlen; ++i)
+    if (s[i] == '\0')
+      break;
+  return i;
+}
+
+#define strnlen xstrnlen
+
+#endif
+
+/* A buffer to read DWARF info.  */
+
+struct dwarf_buf
+{
+  /* Buffer name for error messages.  */
+  const char *name;
+  /* Start of the buffer.  */
+  const unsigned char *start;
+  /* Next byte to read.  */
+  const unsigned char *buf;
+  /* The number of bytes remaining.  */
+  size_t left;
+  /* Whether the data is big-endian.  */
+  int is_bigendian;
+  /* Error callback routine.  */
+  backtrace_error_callback error_callback;
+  /* Data for error_callback.  */
+  void *data;
+  /* Non-zero if we've reported an underflow error.  */
+  int reported_underflow;
+};
+
+/* A single attribute in a DWARF abbreviation.  */
+
+struct attr
+{
+  /* The attribute name.  */
+  enum dwarf_attribute name;
+  /* The attribute form.  */
+  enum dwarf_form form;
+};
+
+/* A single DWARF abbreviation.  */
+
+struct abbrev
+{
+  /* The abbrev code--the number used to refer to the abbrev.  */
+  uint64_t code;
+  /* The entry tag.  */
+  enum dwarf_tag tag;
+  /* Non-zero if this abbrev has child entries.  */
+  int has_children;
+  /* The number of attributes.  */
+  size_t num_attrs;
+  /* The attributes.  */
+  struct attr *attrs;
+};
+
+/* The DWARF abbreviations for a compilation unit.  This structure
+   only exists while reading the compilation unit.  Most DWARF readers
+   seem to a hash table to map abbrev ID's to abbrev entries.
+   However, we primarily care about GCC, and GCC simply issues ID's in
+   numerical order starting at 1.  So we simply keep a sorted vector,
+   and try to just look up the code.  */
+
+struct abbrevs
+{
+  /* The number of abbrevs in the vector.  */
+  size_t num_abbrevs;
+  /* The abbrevs, sorted by the code field.  */
+  struct abbrev *abbrevs;
+};
+
+/* The different kinds of attribute values.  */
+
+enum attr_val_encoding
+{
+  /* An address.  */
+  ATTR_VAL_ADDRESS,
+  /* A unsigned integer.  */
+  ATTR_VAL_UINT,
+  /* A sigd integer.  */
+  ATTR_VAL_SINT,
+  /* A string.  */
+  ATTR_VAL_STRING,
+  /* An offset to other data in the containing unit.  */
+  ATTR_VAL_REF_UNIT,
+  /* An offset to other data within the .dwarf_info section.  */
+  ATTR_VAL_REF_INFO,
+  /* An offset to data in some other section.  */
+  ATTR_VAL_REF_SECTION,
+  /* A type signature.  */
+  ATTR_VAL_REF_TYPE,
+  /* A block of data (not represented).  */
+  ATTR_VAL_BLOCK,
+  /* An expression (not represented).  */
+  ATTR_VAL_EXPR,
+};
+
+/* An attribute value.  */
+
+struct attr_val
+{
+  /* How the value is stored in the field u.  */
+  enum attr_val_encoding encoding;
+  union
+  {
+    /* ATTR_VAL_ADDRESS, ATTR_VAL_UINT, ATTR_VAL_REF*.  */
+    uint64_t uint;
+    /* ATTR_VAL_SINT.  */
+    int64_t sint;
+    /* ATTR_VAL_STRING.  */
+    const char *string;
+    /* ATTR_VAL_BLOCK not stored.  */
+  } u;
+};
+
+/* The line number program header.  */
+
+struct line_header
+{
+  /* The version of the line number information.  */
+  int version;
+  /* The minimum instruction length.  */
+  unsigned int min_insn_len;
+  /* The maximum number of ops per instruction.  */
+  unsigned int max_ops_per_insn;
+  /* The line base for special opcodes.  */
+  int line_base;
+  /* The line range for special opcodes.  */
+  unsigned int line_range;
+  /* The opcode base--the first special opcode.  */
+  unsigned int opcode_base;
+  /* Opcode lengths, indexed by opcode - 1.  */
+  const unsigned char *opcode_lengths;
+  /* The number of directory entries.  */
+  size_t dirs_count;
+  /* The directory entries.  */
+  const char **dirs;
+  /* The number of filenames.  */
+  size_t filenames_count;
+  /* The filenames.  */
+  const char **filenames;
+};
+
+/* Map a single PC value to a file/line.  We will keep a vector of
+   these sorted by PC value.  Each file/line will be correct from the
+   PC up to the PC of the next entry if there is one.  We allocate one
+   extra entry at the end so that we can use bsearch.  */
+
+struct line
+{
+  /* PC.  */
+  uintptr_t pc;
+  /* File name.  Many entries in the array are expected to point to
+     the same file name.  */
+  const char *filename;
+  /* Line number.  */
+  int lineno;
+  /* Index of the object in the original array read from the DWARF
+     section, before it has been sorted.  The index makes it possible
+     to use Quicksort and maintain stability.  */
+  int idx;
+};
+
+/* A growable vector of line number information.  This is used while
+   reading the line numbers.  */
+
+struct line_vector
+{
+  /* Memory.  This is an array of struct line.  */
+  struct backtrace_vector vec;
+  /* Number of valid mappings.  */
+  size_t count;
+};
+
+/* A function described in the debug info.  */
+
+struct function
+{
+  /* The name of the function.  */
+  const char *name;
+  /* If this is an inlined function, the filename of the call
+     site.  */
+  const char *caller_filename;
+  /* If this is an inlined function, the line number of the call
+     site.  */
+  int caller_lineno;
+  /* Map PC ranges to inlined functions.  */
+  struct function_addrs *function_addrs;
+  size_t function_addrs_count;
+};
+
+/* An address range for a function.  This maps a PC value to a
+   specific function.  */
+
+struct function_addrs
+{
+  /* Range is LOW <= PC < HIGH.  */
+  uint64_t low;
+  uint64_t high;
+  /* Function for this address range.  */
+  struct function *function;
+};
+
+/* A growable vector of function address ranges.  */
+
+struct function_vector
+{
+  /* Memory.  This is an array of struct function_addrs.  */
+  struct backtrace_vector vec;
+  /* Number of address ranges present.  */
+  size_t count;
+};
+
+/* A DWARF compilation unit.  This only holds the information we need
+   to map a PC to a file and line.  */
+
+struct unit
+{
+  /* The first entry for this compilation unit.  */
+  const unsigned char *unit_data;
+  /* The length of the data for this compilation unit.  */
+  size_t unit_data_len;
+  /* The offset of UNIT_DATA from the start of the information for
+     this compilation unit.  */
+  size_t unit_data_offset;
+  /* DWARF version.  */
+  int version;
+  /* Whether unit is DWARF64.  */
+  int is_dwarf64;
+  /* Address size.  */
+  int addrsize;
+  /* Offset into line number information.  */
+  off_t lineoff;
+  /* Primary source file.  */
+  const char *filename;
+  /* Compilation command working directory.  */
+  const char *comp_dir;
+  /* Absolute file name, only set if needed.  */
+  const char *abs_filename;
+  /* The abbreviations for this unit.  */
+  struct abbrevs abbrevs;
+
+  /* The fields above this point are read in during initialization and
+     may be accessed freely.  The fields below this point are read in
+     as needed, and therefore require care, as different threads may
+     try to initialize them simultaneously.  */
+
+  /* PC to line number mapping.  This is NULL if the values have not
+     been read.  This is (struct line *) -1 if there was an error
+     reading the values.  */
+  struct line *lines;
+  /* Number of entries in lines.  */
+  size_t lines_count;
+  /* PC ranges to function.  */
+  struct function_addrs *function_addrs;
+  size_t function_addrs_count;
+};
+
+/* An address range for a compilation unit.  This maps a PC value to a
+   specific compilation unit.  Note that we invert the representation
+   in DWARF: instead of listing the units and attaching a list of
+   ranges, we list the ranges and have each one point to the unit.
+   This lets us do a binary search to find the unit.  */
+
+struct unit_addrs
+{
+  /* Range is LOW <= PC < HIGH.  */
+  uint64_t low;
+  uint64_t high;
+  /* Compilation unit for this address range.  */
+  struct unit *u;
+};
+
+/* A growable vector of compilation unit address ranges.  */
+
+struct unit_addrs_vector
+{
+  /* Memory.  This is an array of struct unit_addrs.  */
+  struct backtrace_vector vec;
+  /* Number of address ranges present.  */
+  size_t count;
+};
+
+/* The information we need to map a PC to a file and line.  */
+
+struct dwarf_data
+{
+  /* The data for the next file we know about.  */
+  struct dwarf_data *next;
+  /* The base address for this file.  */
+  uintptr_t base_address;
+  /* A sorted list of address ranges.  */
+  struct unit_addrs *addrs;
+  /* Number of address ranges in list.  */
+  size_t addrs_count;
+  /* The unparsed .debug_info section.  */
+  const unsigned char *dwarf_info;
+  size_t dwarf_info_size;
+  /* The unparsed .debug_line section.  */
+  const unsigned char *dwarf_line;
+  size_t dwarf_line_size;
+  /* The unparsed .debug_ranges section.  */
+  const unsigned char *dwarf_ranges;
+  size_t dwarf_ranges_size;
+  /* The unparsed .debug_str section.  */
+  const unsigned char *dwarf_str;
+  size_t dwarf_str_size;
+  /* Whether the data is big-endian or not.  */
+  int is_bigendian;
+  /* A vector used for function addresses.  We keep this here so that
+     we can grow the vector as we read more functions.  */
+  struct function_vector fvec;
+};
+
+/* Report an error for a DWARF buffer.  */
+
+static void
+dwarf_buf_error (struct dwarf_buf *buf, const char *msg)
+{
+  char b[200];
+
+  snprintf (b, sizeof b, "%s in %s at %d",
+	    msg, buf->name, (int) (buf->buf - buf->start));
+  buf->error_callback (buf->data, b, 0);
+}
+
+/* Require at least COUNT bytes in BUF.  Return 1 if all is well, 0 on
+   error.  */
+
+static int
+require (struct dwarf_buf *buf, size_t count)
+{
+  if (buf->left >= count)
+    return 1;
+
+  if (!buf->reported_underflow)
+    {
+      dwarf_buf_error (buf, "DWARF underflow");
+      buf->reported_underflow = 1;
+    }
+
+  return 0;
+}
+
+/* Advance COUNT bytes in BUF.  Return 1 if all is well, 0 on
+   error.  */
+
+static int
+advance (struct dwarf_buf *buf, size_t count)
+{
+  if (!require (buf, count))
+    return 0;
+  buf->buf += count;
+  buf->left -= count;
+  return 1;
+}
+
+/* Read one byte from BUF and advance 1 byte.  */
+
+static unsigned char
+read_byte (struct dwarf_buf *buf)
+{
+  const unsigned char *p = buf->buf;
+
+  if (!advance (buf, 1))
+    return 0;
+  return p[0];
+}
+
+/* Read a signed char from BUF and advance 1 byte.  */
+
+static signed char
+read_sbyte (struct dwarf_buf *buf)
+{
+  const unsigned char *p = buf->buf;
+
+  if (!advance (buf, 1))
+    return 0;
+  return (*p ^ 0x80) - 0x80;
+}
+
+/* Read a uint16 from BUF and advance 2 bytes.  */
+
+static uint16_t
+read_uint16 (struct dwarf_buf *buf)
+{
+  const unsigned char *p = buf->buf;
+
+  if (!advance (buf, 2))
+    return 0;
+  if (buf->is_bigendian)
+    return ((uint16_t) p[0] << 8) | (uint16_t) p[1];
+  else
+    return ((uint16_t) p[1] << 8) | (uint16_t) p[0];
+}
+
+/* Read a uint32 from BUF and advance 4 bytes.  */
+
+static uint32_t
+read_uint32 (struct dwarf_buf *buf)
+{
+  const unsigned char *p = buf->buf;
+
+  if (!advance (buf, 4))
+    return 0;
+  if (buf->is_bigendian)
+    return (((uint32_t) p[0] << 24) | ((uint32_t) p[1] << 16)
+	    | ((uint32_t) p[2] << 8) | (uint32_t) p[3]);
+  else
+    return (((uint32_t) p[3] << 24) | ((uint32_t) p[2] << 16)
+	    | ((uint32_t) p[1] << 8) | (uint32_t) p[0]);
+}
+
+/* Read a uint64 from BUF and advance 8 bytes.  */
+
+static uint64_t
+read_uint64 (struct dwarf_buf *buf)
+{
+  const unsigned char *p = buf->buf;
+
+  if (!advance (buf, 8))
+    return 0;
+  if (buf->is_bigendian)
+    return (((uint64_t) p[0] << 56) | ((uint64_t) p[1] << 48)
+	    | ((uint64_t) p[2] << 40) | ((uint64_t) p[3] << 32)
+	    | ((uint64_t) p[4] << 24) | ((uint64_t) p[5] << 16)
+	    | ((uint64_t) p[6] << 8) | (uint64_t) p[7]);
+  else
+    return (((uint64_t) p[7] << 56) | ((uint64_t) p[6] << 48)
+	    | ((uint64_t) p[5] << 40) | ((uint64_t) p[4] << 32)
+	    | ((uint64_t) p[3] << 24) | ((uint64_t) p[2] << 16)
+	    | ((uint64_t) p[1] << 8) | (uint64_t) p[0]);
+}
+
+/* Read an offset from BUF and advance the appropriate number of
+   bytes.  */
+
+static uint64_t
+read_offset (struct dwarf_buf *buf, int is_dwarf64)
+{
+  if (is_dwarf64)
+    return read_uint64 (buf);
+  else
+    return read_uint32 (buf);
+}
+
+/* Read an address from BUF and advance the appropriate number of
+   bytes.  */
+
+static uint64_t
+read_address (struct dwarf_buf *buf, int addrsize)
+{
+  switch (addrsize)
+    {
+    case 1:
+      return read_byte (buf);
+    case 2:
+      return read_uint16 (buf);
+    case 4:
+      return read_uint32 (buf);
+    case 8:
+      return read_uint64 (buf);
+    default:
+      dwarf_buf_error (buf, "unrecognized address size");
+      return 0;
+    }
+}
+
+/* Return whether a value is the highest possible address, given the
+   address size.  */
+
+static int
+is_highest_address (uint64_t address, int addrsize)
+{
+  switch (addrsize)
+    {
+    case 1:
+      return address == (unsigned char) -1;
+    case 2:
+      return address == (uint16_t) -1;
+    case 4:
+      return address == (uint32_t) -1;
+    case 8:
+      return address == (uint64_t) -1;
+    default:
+      return 0;
+    }
+}
+
+/* Read an unsigned LEB128 number.  */
+
+static uint64_t
+read_uleb128 (struct dwarf_buf *buf)
+{
+  uint64_t ret;
+  unsigned int shift;
+  int overflow;
+  unsigned char b;
+
+  ret = 0;
+  shift = 0;
+  overflow = 0;
+  do
+    {
+      const unsigned char *p;
+
+      p = buf->buf;
+      if (!advance (buf, 1))
+	return 0;
+      b = *p;
+      if (shift < 64)
+	ret |= ((uint64_t) (b & 0x7f)) << shift;
+      else if (!overflow)
+	{
+	  dwarf_buf_error (buf, "LEB128 overflows uint64_t");
+	  overflow = 1;
+	}
+      shift += 7;
+    }
+  while ((b & 0x80) != 0);
+
+  return ret;
+}
+
+/* Read a signed LEB128 number.  */
+
+static int64_t
+read_sleb128 (struct dwarf_buf *buf)
+{
+  uint64_t val;
+  unsigned int shift;
+  int overflow;
+  unsigned char b;
+
+  val = 0;
+  shift = 0;
+  overflow = 0;
+  do
+    {
+      const unsigned char *p;
+
+      p = buf->buf;
+      if (!advance (buf, 1))
+	return 0;
+      b = *p;
+      if (shift < 64)
+	val |= ((uint64_t) (b & 0x7f)) << shift;
+      else if (!overflow)
+	{
+	  dwarf_buf_error (buf, "signed LEB128 overflows uint64_t");
+	  overflow = 1;
+	}
+      shift += 7;
+    }
+  while ((b & 0x80) != 0);
+
+  if ((b & 0x40) != 0 && shift < 64)
+    val |= ((uint64_t) -1) << shift;
+
+  return (int64_t) val;
+}
+
+/* Return the length of an LEB128 number.  */
+
+static size_t
+leb128_len (const unsigned char *p)
+{
+  size_t ret;
+
+  ret = 1;
+  while ((*p & 0x80) != 0)
+    {
+      ++p;
+      ++ret;
+    }
+  return ret;
+}
+
+/* Free an abbreviations structure.  */
+
+static void
+free_abbrevs (struct backtrace_state *state, struct abbrevs *abbrevs,
+	      backtrace_error_callback error_callback, void *data)
+{
+  size_t i;
+
+  for (i = 0; i < abbrevs->num_abbrevs; ++i)
+    backtrace_free (state, abbrevs->abbrevs[i].attrs,
+		    abbrevs->abbrevs[i].num_attrs * sizeof (struct attr),
+		    error_callback, data);
+  backtrace_free (state, abbrevs->abbrevs,
+		  abbrevs->num_abbrevs * sizeof (struct abbrev),
+		  error_callback, data);
+  abbrevs->num_abbrevs = 0;
+  abbrevs->abbrevs = NULL;
+}
+
+/* Read an attribute value.  Returns 1 on success, 0 on failure.  If
+   the value can be represented as a uint64_t, sets *VAL and sets
+   *IS_VALID to 1.  We don't try to store the value of other attribute
+   forms, because we don't care about them.  */
+
+static int
+read_attribute (enum dwarf_form form, struct dwarf_buf *buf,
+		int is_dwarf64, int version, int addrsize,
+		const unsigned char *dwarf_str, size_t dwarf_str_size,
+		struct attr_val *val)
+{
+  /* Avoid warnings about val.u.FIELD may be used uninitialized if
+     this function is inlined.  The warnings aren't valid but can
+     occur because the different fields are set and used
+     conditionally.  */
+  memset (val, 0, sizeof *val);
+
+  switch (form)
+    {
+    case DW_FORM_addr:
+      val->encoding = ATTR_VAL_ADDRESS;
+      val->u.uint = read_address (buf, addrsize);
+      return 1;
+    case DW_FORM_block2:
+      val->encoding = ATTR_VAL_BLOCK;
+      return advance (buf, read_uint16 (buf));
+    case DW_FORM_block4:
+      val->encoding = ATTR_VAL_BLOCK;
+      return advance (buf, read_uint32 (buf));
+    case DW_FORM_data2:
+      val->encoding = ATTR_VAL_UINT;
+      val->u.uint = read_uint16 (buf);
+      return 1;
+    case DW_FORM_data4:
+      val->encoding = ATTR_VAL_UINT;
+      val->u.uint = read_uint32 (buf);
+      return 1;
+    case DW_FORM_data8:
+      val->encoding = ATTR_VAL_UINT;
+      val->u.uint = read_uint64 (buf);
+      return 1;
+    case DW_FORM_string:
+      val->encoding = ATTR_VAL_STRING;
+      val->u.string = (const char *) buf->buf;
+      return advance (buf, strnlen ((const char *) buf->buf, buf->left) + 1);
+    case DW_FORM_block:
+      val->encoding = ATTR_VAL_BLOCK;
+      return advance (buf, read_uleb128 (buf));
+    case DW_FORM_block1:
+      val->encoding = ATTR_VAL_BLOCK;
+      return advance (buf, read_byte (buf));
+    case DW_FORM_data1:
+      val->encoding = ATTR_VAL_UINT;
+      val->u.uint = read_byte (buf);
+      return 1;
+    case DW_FORM_flag:
+      val->encoding = ATTR_VAL_UINT;
+      val->u.uint = read_byte (buf);
+      return 1;
+    case DW_FORM_sdata:
+      val->encoding = ATTR_VAL_SINT;
+      val->u.sint = read_sleb128 (buf);
+      return 1;
+    case DW_FORM_strp:
+      {
+	uint64_t offset;
+
+	offset = read_offset (buf, is_dwarf64);
+	if (offset >= dwarf_str_size)
+	  {
+	    dwarf_buf_error (buf, "DW_FORM_strp out of range");
+	    return 0;
+	  }
+	val->encoding = ATTR_VAL_STRING;
+	val->u.string = (const char *) dwarf_str + offset;
+	return 1;
+      }
+    case DW_FORM_udata:
+      val->encoding = ATTR_VAL_UINT;
+      val->u.uint = read_uleb128 (buf);
+      return 1;
+    case DW_FORM_ref_addr:
+      val->encoding = ATTR_VAL_REF_INFO;
+      if (version == 2)
+	val->u.uint = read_address (buf, addrsize);
+      else
+	val->u.uint = read_offset (buf, is_dwarf64);
+      return 1;
+    case DW_FORM_ref1:
+      val->encoding = ATTR_VAL_REF_UNIT;
+      val->u.uint = read_byte (buf);
+      return 1;
+    case DW_FORM_ref2:
+      val->encoding = ATTR_VAL_REF_UNIT;
+      val->u.uint = read_uint16 (buf);
+      return 1;
+    case DW_FORM_ref4:
+      val->encoding = ATTR_VAL_REF_UNIT;
+      val->u.uint = read_uint32 (buf);
+      return 1;
+    case DW_FORM_ref8:
+      val->encoding = ATTR_VAL_REF_UNIT;
+      val->u.uint = read_uint64 (buf);
+      return 1;
+    case DW_FORM_ref_udata:
+      val->encoding = ATTR_VAL_REF_UNIT;
+      val->u.uint = read_uleb128 (buf);
+      return 1;
+    case DW_FORM_indirect:
+      {
+	uint64_t form1;
+
+	form1 = read_uleb128 (buf);
+	return read_attribute ((enum dwarf_form) form1, buf, is_dwarf64,
+			       version, addrsize, dwarf_str, dwarf_str_size,
+			       val);
+      }
+    case DW_FORM_sec_offset:
+      val->encoding = ATTR_VAL_REF_SECTION;
+      val->u.uint = read_offset (buf, is_dwarf64);
+      return 1;
+    case DW_FORM_exprloc:
+      val->encoding = ATTR_VAL_EXPR;
+      return advance (buf, read_uleb128 (buf));
+    case DW_FORM_flag_present:
+      val->encoding = ATTR_VAL_UINT;
+      val->u.uint = 1;
+      return 1;
+    case DW_FORM_ref_sig8:
+      val->encoding = ATTR_VAL_REF_TYPE;
+      val->u.uint = read_uint64 (buf);
+      return 1;
+    case DW_FORM_GNU_addr_index:
+      val->encoding = ATTR_VAL_REF_SECTION;
+      val->u.uint = read_uleb128 (buf);
+      return 1;
+    case DW_FORM_GNU_str_index:
+      val->encoding = ATTR_VAL_REF_SECTION;
+      val->u.uint = read_uleb128 (buf);
+      return 1;
+    case DW_FORM_GNU_ref_alt:
+      val->encoding = ATTR_VAL_REF_SECTION;
+      val->u.uint = read_offset (buf, is_dwarf64);
+      return 1;
+    case DW_FORM_GNU_strp_alt:
+      val->encoding = ATTR_VAL_REF_SECTION;
+      val->u.uint = read_offset (buf, is_dwarf64);
+      return 1;
+    default:
+      dwarf_buf_error (buf, "unrecognized DWARF form");
+      return 0;
+    }
+}
+
+/* Compare function_addrs for qsort.  When ranges are nested, make the
+   smallest one sort last.  */
+
+static int
+function_addrs_compare (const void *v1, const void *v2)
+{
+  const struct function_addrs *a1 = (const struct function_addrs *) v1;
+  const struct function_addrs *a2 = (const struct function_addrs *) v2;
+
+  if (a1->low < a2->low)
+    return -1;
+  if (a1->low > a2->low)
+    return 1;
+  if (a1->high < a2->high)
+    return 1;
+  if (a1->high > a2->high)
+    return -1;
+  return strcmp (a1->function->name, a2->function->name);
+}
+
+/* Compare a PC against a function_addrs for bsearch.  Note that if
+   there are multiple ranges containing PC, which one will be returned
+   is unpredictable.  We compensate for that in dwarf_fileline.  */
+
+static int
+function_addrs_search (const void *vkey, const void *ventry)
+{
+  const uintptr_t *key = (const uintptr_t *) vkey;
+  const struct function_addrs *entry = (const struct function_addrs *) ventry;
+  uintptr_t pc;
+
+  pc = *key;
+  if (pc < entry->low)
+    return -1;
+  else if (pc >= entry->high)
+    return 1;
+  else
+    return 0;
+}
+
+/* Add a new compilation unit address range to a vector.  Returns 1 on
+   success, 0 on failure.  */
+
+static int
+add_unit_addr (struct backtrace_state *state, uintptr_t base_address,
+	       struct unit_addrs addrs,
+	       backtrace_error_callback error_callback, void *data,
+	       struct unit_addrs_vector *vec)
+{
+  struct unit_addrs *p;
+
+  /* Add in the base address of the module here, so that we can look
+     up the PC directly.  */
+  addrs.low += base_address;
+  addrs.high += base_address;
+
+  /* Try to merge with the last entry.  */
+  if (vec->count > 0)
+    {
+      p = (struct unit_addrs *) vec->vec.base + (vec->count - 1);
+      if ((addrs.low == p->high || addrs.low == p->high + 1)
+	  && addrs.u == p->u)
+	{
+	  if (addrs.high > p->high)
+	    p->high = addrs.high;
+	  return 1;
+	}
+    }
+
+  p = ((struct unit_addrs *)
+       backtrace_vector_grow (state, sizeof (struct unit_addrs),
+			      error_callback, data, &vec->vec));
+  if (p == NULL)
+    return 0;
+
+  *p = addrs;
+  ++vec->count;
+  return 1;
+}
+
+/* Free a unit address vector.  */
+
+static void
+free_unit_addrs_vector (struct backtrace_state *state,
+			struct unit_addrs_vector *vec,
+			backtrace_error_callback error_callback, void *data)
+{
+  struct unit_addrs *addrs;
+  size_t i;
+
+  addrs = (struct unit_addrs *) vec->vec.base;
+  for (i = 0; i < vec->count; ++i)
+    free_abbrevs (state, &addrs[i].u->abbrevs, error_callback, data);
+}
+
+/* Compare unit_addrs for qsort.  When ranges are nested, make the
+   smallest one sort last.  */
+
+static int
+unit_addrs_compare (const void *v1, const void *v2)
+{
+  const struct unit_addrs *a1 = (const struct unit_addrs *) v1;
+  const struct unit_addrs *a2 = (const struct unit_addrs *) v2;
+
+  if (a1->low < a2->low)
+    return -1;
+  if (a1->low > a2->low)
+    return 1;
+  if (a1->high < a2->high)
+    return 1;
+  if (a1->high > a2->high)
+    return -1;
+  if (a1->u->lineoff < a2->u->lineoff)
+    return -1;
+  if (a1->u->lineoff > a2->u->lineoff)
+    return 1;
+  return 0;
+}
+
+/* Compare a PC against a unit_addrs for bsearch.  Note that if there
+   are multiple ranges containing PC, which one will be returned is
+   unpredictable.  We compensate for that in dwarf_fileline.  */
+
+static int
+unit_addrs_search (const void *vkey, const void *ventry)
+{
+  const uintptr_t *key = (const uintptr_t *) vkey;
+  const struct unit_addrs *entry = (const struct unit_addrs *) ventry;
+  uintptr_t pc;
+
+  pc = *key;
+  if (pc < entry->low)
+    return -1;
+  else if (pc >= entry->high)
+    return 1;
+  else
+    return 0;
+}
+
+/* Sort the line vector by PC.  We want a stable sort here to maintain
+   the order of lines for the same PC values.  Since the sequence is
+   being sorted in place, their addresses cannot be relied on to
+   maintain stability.  That is the purpose of the index member.  */
+
+static int
+line_compare (const void *v1, const void *v2)
+{
+  const struct line *ln1 = (const struct line *) v1;
+  const struct line *ln2 = (const struct line *) v2;
+
+  if (ln1->pc < ln2->pc)
+    return -1;
+  else if (ln1->pc > ln2->pc)
+    return 1;
+  else if (ln1->idx < ln2->idx)
+    return -1;
+  else if (ln1->idx > ln2->idx)
+    return 1;
+  else
+    return 0;
+}
+
+/* Find a PC in a line vector.  We always allocate an extra entry at
+   the end of the lines vector, so that this routine can safely look
+   at the next entry.  Note that when there are multiple mappings for
+   the same PC value, this will return the last one.  */
+
+static int
+line_search (const void *vkey, const void *ventry)
+{
+  const uintptr_t *key = (const uintptr_t *) vkey;
+  const struct line *entry = (const struct line *) ventry;
+  uintptr_t pc;
+
+  pc = *key;
+  if (pc < entry->pc)
+    return -1;
+  else if (pc >= (entry + 1)->pc)
+    return 1;
+  else
+    return 0;
+}
+
+/* Sort the abbrevs by the abbrev code.  This function is passed to
+   both qsort and bsearch.  */
+
+static int
+abbrev_compare (const void *v1, const void *v2)
+{
+  const struct abbrev *a1 = (const struct abbrev *) v1;
+  const struct abbrev *a2 = (const struct abbrev *) v2;
+
+  if (a1->code < a2->code)
+    return -1;
+  else if (a1->code > a2->code)
+    return 1;
+  else
+    {
+      /* This really shouldn't happen.  It means there are two
+	 different abbrevs with the same code, and that means we don't
+	 know which one lookup_abbrev should return.  */
+      return 0;
+    }
+}
+
+/* Read the abbreviation table for a compilation unit.  Returns 1 on
+   success, 0 on failure.  */
+
+static int
+read_abbrevs (struct backtrace_state *state, uint64_t abbrev_offset,
+	      const unsigned char *dwarf_abbrev, size_t dwarf_abbrev_size,
+	      int is_bigendian, backtrace_error_callback error_callback,
+	      void *data, struct abbrevs *abbrevs)
+{
+  struct dwarf_buf abbrev_buf;
+  struct dwarf_buf count_buf;
+  size_t num_abbrevs;
+
+  abbrevs->num_abbrevs = 0;
+  abbrevs->abbrevs = NULL;
+
+  if (abbrev_offset >= dwarf_abbrev_size)
+    {
+      error_callback (data, "abbrev offset out of range", 0);
+      return 0;
+    }
+
+  abbrev_buf.name = ".debug_abbrev";
+  abbrev_buf.start = dwarf_abbrev;
+  abbrev_buf.buf = dwarf_abbrev + abbrev_offset;
+  abbrev_buf.left = dwarf_abbrev_size - abbrev_offset;
+  abbrev_buf.is_bigendian = is_bigendian;
+  abbrev_buf.error_callback = error_callback;
+  abbrev_buf.data = data;
+  abbrev_buf.reported_underflow = 0;
+
+  /* Count the number of abbrevs in this list.  */
+
+  count_buf = abbrev_buf;
+  num_abbrevs = 0;
+  while (read_uleb128 (&count_buf) != 0)
+    {
+      if (count_buf.reported_underflow)
+	return 0;
+      ++num_abbrevs;
+      // Skip tag.
+      read_uleb128 (&count_buf);
+      // Skip has_children.
+      read_byte (&count_buf);
+      // Skip attributes.
+      while (read_uleb128 (&count_buf) != 0)
+	read_uleb128 (&count_buf);
+      // Skip form of last attribute.
+      read_uleb128 (&count_buf);
+    }
+
+  if (count_buf.reported_underflow)
+    return 0;
+
+  if (num_abbrevs == 0)
+    return 1;
+
+  abbrevs->num_abbrevs = num_abbrevs;
+  abbrevs->abbrevs = ((struct abbrev *)
+		      backtrace_alloc (state,
+				       num_abbrevs * sizeof (struct abbrev),
+				       error_callback, data));
+  if (abbrevs->abbrevs == NULL)
+    return 0;
+  memset (abbrevs->abbrevs, 0, num_abbrevs * sizeof (struct abbrev));
+
+  num_abbrevs = 0;
+  while (1)
+    {
+      uint64_t code;
+      struct abbrev a;
+      size_t num_attrs;
+      struct attr *attrs;
+
+      if (abbrev_buf.reported_underflow)
+	goto fail;
+
+      code = read_uleb128 (&abbrev_buf);
+      if (code == 0)
+	break;
+
+      a.code = code;
+      a.tag = (enum dwarf_tag) read_uleb128 (&abbrev_buf);
+      a.has_children = read_byte (&abbrev_buf);
+
+      count_buf = abbrev_buf;
+      num_attrs = 0;
+      while (read_uleb128 (&count_buf) != 0)
+	{
+	  ++num_attrs;
+	  read_uleb128 (&count_buf);
+	}
+
+      if (num_attrs == 0)
+	{
+	  attrs = NULL;
+	  read_uleb128 (&abbrev_buf);
+	  read_uleb128 (&abbrev_buf);
+	}
+      else
+	{
+	  attrs = ((struct attr *)
+		   backtrace_alloc (state, num_attrs * sizeof *attrs,
+				    error_callback, data));
+	  if (attrs == NULL)
+	    goto fail;
+	  num_attrs = 0;
+	  while (1)
+	    {
+	      uint64_t name;
+	      uint64_t form;
+
+	      name = read_uleb128 (&abbrev_buf);
+	      form = read_uleb128 (&abbrev_buf);
+	      if (name == 0)
+		break;
+	      attrs[num_attrs].name = (enum dwarf_attribute) name;
+	      attrs[num_attrs].form = (enum dwarf_form) form;
+	      ++num_attrs;
+	    }
+	}
+
+      a.num_attrs = num_attrs;
+      a.attrs = attrs;
+
+      abbrevs->abbrevs[num_abbrevs] = a;
+      ++num_abbrevs;
+    }
+
+  backtrace_qsort (abbrevs->abbrevs, abbrevs->num_abbrevs,
+		   sizeof (struct abbrev), abbrev_compare);
+
+  return 1;
+
+ fail:
+  free_abbrevs (state, abbrevs, error_callback, data);
+  return 0;
+}
+
+/* Return the abbrev information for an abbrev code.  */
+
+static const struct abbrev *
+lookup_abbrev (struct abbrevs *abbrevs, uint64_t code,
+	       backtrace_error_callback error_callback, void *data)
+{
+  struct abbrev key;
+  void *p;
+
+  /* With GCC, where abbrevs are simply numbered in order, we should
+     be able to just look up the entry.  */
+  if (code - 1 < abbrevs->num_abbrevs
+      && abbrevs->abbrevs[code - 1].code == code)
+    return &abbrevs->abbrevs[code - 1];
+
+  /* Otherwise we have to search.  */
+  memset (&key, 0, sizeof key);
+  key.code = code;
+  p = bsearch (&key, abbrevs->abbrevs, abbrevs->num_abbrevs,
+	       sizeof (struct abbrev), abbrev_compare);
+  if (p == NULL)
+    {
+      error_callback (data, "invalid abbreviation code", 0);
+      return NULL;
+    }
+  return (const struct abbrev *) p;
+}
+
+/* Add non-contiguous address ranges for a compilation unit.  Returns
+   1 on success, 0 on failure.  */
+
+static int
+add_unit_ranges (struct backtrace_state *state, uintptr_t base_address,
+		 struct unit *u, uint64_t ranges, uint64_t base,
+		 int is_bigendian, const unsigned char *dwarf_ranges,
+		 size_t dwarf_ranges_size,
+		 backtrace_error_callback error_callback, void *data,
+		 struct unit_addrs_vector *addrs)
+{
+  struct dwarf_buf ranges_buf;
+
+  if (ranges >= dwarf_ranges_size)
+    {
+      error_callback (data, "ranges offset out of range", 0);
+      return 0;
+    }
+
+  ranges_buf.name = ".debug_ranges";
+  ranges_buf.start = dwarf_ranges;
+  ranges_buf.buf = dwarf_ranges + ranges;
+  ranges_buf.left = dwarf_ranges_size - ranges;
+  ranges_buf.is_bigendian = is_bigendian;
+  ranges_buf.error_callback = error_callback;
+  ranges_buf.data = data;
+  ranges_buf.reported_underflow = 0;
+
+  while (1)
+    {
+      uint64_t low;
+      uint64_t high;
+
+      if (ranges_buf.reported_underflow)
+	return 0;
+
+      low = read_address (&ranges_buf, u->addrsize);
+      high = read_address (&ranges_buf, u->addrsize);
+
+      if (low == 0 && high == 0)
+	break;
+
+      if (is_highest_address (low, u->addrsize))
+	base = high;
+      else
+	{
+	  struct unit_addrs a;
+
+	  a.low = low + base;
+	  a.high = high + base;
+	  a.u = u;
+	  if (!add_unit_addr (state, base_address, a, error_callback, data,
+			      addrs))
+	    return 0;
+	}
+    }
+
+  if (ranges_buf.reported_underflow)
+    return 0;
+
+  return 1;
+}
+
+/* Find the address range covered by a compilation unit, reading from
+   UNIT_BUF and adding values to U.  Returns 1 if all data could be
+   read, 0 if there is some error.  */
+
+static int
+find_address_ranges (struct backtrace_state *state, uintptr_t base_address,
+		     struct dwarf_buf *unit_buf,
+		     const unsigned char *dwarf_str, size_t dwarf_str_size,
+		     const unsigned char *dwarf_ranges,
+		     size_t dwarf_ranges_size,
+		     int is_bigendian, backtrace_error_callback error_callback,
+		     void *data, struct unit *u,
+		     struct unit_addrs_vector *addrs)
+{
+  while (unit_buf->left > 0)
+    {
+      uint64_t code;
+      const struct abbrev *abbrev;
+      uint64_t lowpc;
+      int have_lowpc;
+      uint64_t highpc;
+      int have_highpc;
+      int highpc_is_relative;
+      uint64_t ranges;
+      int have_ranges;
+      size_t i;
+
+      code = read_uleb128 (unit_buf);
+      if (code == 0)
+	return 1;
+
+      abbrev = lookup_abbrev (&u->abbrevs, code, error_callback, data);
+      if (abbrev == NULL)
+	return 0;
+
+      lowpc = 0;
+      have_lowpc = 0;
+      highpc = 0;
+      have_highpc = 0;
+      highpc_is_relative = 0;
+      ranges = 0;
+      have_ranges = 0;
+      for (i = 0; i < abbrev->num_attrs; ++i)
+	{
+	  struct attr_val val;
+
+	  if (!read_attribute (abbrev->attrs[i].form, unit_buf,
+			       u->is_dwarf64, u->version, u->addrsize,
+			       dwarf_str, dwarf_str_size, &val))
+	    return 0;
+
+	  switch (abbrev->attrs[i].name)
+	    {
+	    case DW_AT_low_pc:
+	      if (val.encoding == ATTR_VAL_ADDRESS)
+		{
+		  lowpc = val.u.uint;
+		  have_lowpc = 1;
+		}
+	      break;
+
+	    case DW_AT_high_pc:
+	      if (val.encoding == ATTR_VAL_ADDRESS)
+		{
+		  highpc = val.u.uint;
+		  have_highpc = 1;
+		}
+	      else if (val.encoding == ATTR_VAL_UINT)
+		{
+		  highpc = val.u.uint;
+		  have_highpc = 1;
+		  highpc_is_relative = 1;
+		}
+	      break;
+
+	    case DW_AT_ranges:
+	      if (val.encoding == ATTR_VAL_UINT
+		  || val.encoding == ATTR_VAL_REF_SECTION)
+		{
+		  ranges = val.u.uint;
+		  have_ranges = 1;
+		}
+	      break;
+
+	    case DW_AT_stmt_list:
+	      if (abbrev->tag == DW_TAG_compile_unit
+		  && (val.encoding == ATTR_VAL_UINT
+		      || val.encoding == ATTR_VAL_REF_SECTION))
+		u->lineoff = val.u.uint;
+	      break;
+
+	    case DW_AT_name:
+	      if (abbrev->tag == DW_TAG_compile_unit
+		  && val.encoding == ATTR_VAL_STRING)
+		u->filename = val.u.string;
+	      break;
+
+	    case DW_AT_comp_dir:
+	      if (abbrev->tag == DW_TAG_compile_unit
+		  && val.encoding == ATTR_VAL_STRING)
+		u->comp_dir = val.u.string;
+	      break;
+
+	    default:
+	      break;
+	    }
+	}
+
+      if (abbrev->tag == DW_TAG_compile_unit
+	  || abbrev->tag == DW_TAG_subprogram)
+	{
+	  if (have_ranges)
+	    {
+	      if (!add_unit_ranges (state, base_address, u, ranges, lowpc,
+				    is_bigendian, dwarf_ranges,
+				    dwarf_ranges_size, error_callback,
+				    data, addrs))
+		return 0;
+	    }
+	  else if (have_lowpc && have_highpc)
+	    {
+	      struct unit_addrs a;
+
+	      if (highpc_is_relative)
+		highpc += lowpc;
+	      a.low = lowpc;
+	      a.high = highpc;
+	      a.u = u;
+
+	      if (!add_unit_addr (state, base_address, a, error_callback, data,
+				  addrs))
+		return 0;
+	    }
+
+	  /* If we found the PC range in the DW_TAG_compile_unit, we
+	     can stop now.  */
+	  if (abbrev->tag == DW_TAG_compile_unit
+	      && (have_ranges || (have_lowpc && have_highpc)))
+	    return 1;
+	}
+
+      if (abbrev->has_children)
+	{
+	  if (!find_address_ranges (state, base_address, unit_buf,
+				    dwarf_str, dwarf_str_size,
+				    dwarf_ranges, dwarf_ranges_size,
+				    is_bigendian, error_callback, data,
+				    u, addrs))
+	    return 0;
+	}
+    }
+
+  return 1;
+}
+
+/* Build a mapping from address ranges to the compilation units where
+   the line number information for that range can be found.  Returns 1
+   on success, 0 on failure.  */
+
+static int
+build_address_map (struct backtrace_state *state, uintptr_t base_address,
+		   const unsigned char *dwarf_info, size_t dwarf_info_size,
+		   const unsigned char *dwarf_abbrev, size_t dwarf_abbrev_size,
+		   const unsigned char *dwarf_ranges, size_t dwarf_ranges_size,
+		   const unsigned char *dwarf_str, size_t dwarf_str_size,
+		   int is_bigendian, backtrace_error_callback error_callback,
+		   void *data, struct unit_addrs_vector *addrs)
+{
+  struct dwarf_buf info;
+  struct abbrevs abbrevs;
+
+  memset (&addrs->vec, 0, sizeof addrs->vec);
+  addrs->count = 0;
+
+  /* Read through the .debug_info section.  FIXME: Should we use the
+     .debug_aranges section?  gdb and addr2line don't use it, but I'm
+     not sure why.  */
+
+  info.name = ".debug_info";
+  info.start = dwarf_info;
+  info.buf = dwarf_info;
+  info.left = dwarf_info_size;
+  info.is_bigendian = is_bigendian;
+  info.error_callback = error_callback;
+  info.data = data;
+  info.reported_underflow = 0;
+
+  memset (&abbrevs, 0, sizeof abbrevs);
+  while (info.left > 0)
+    {
+      const unsigned char *unit_data_start;
+      uint64_t len;
+      int is_dwarf64;
+      struct dwarf_buf unit_buf;
+      int version;
+      uint64_t abbrev_offset;
+      int addrsize;
+      struct unit *u;
+
+      if (info.reported_underflow)
+	goto fail;
+
+      unit_data_start = info.buf;
+
+      is_dwarf64 = 0;
+      len = read_uint32 (&info);
+      if (len == 0xffffffff)
+	{
+	  len = read_uint64 (&info);
+	  is_dwarf64 = 1;
+	}
+
+      unit_buf = info;
+      unit_buf.left = len;
+
+      if (!advance (&info, len))
+	goto fail;
+
+      version = read_uint16 (&unit_buf);
+      if (version < 2 || version > 4)
+	{
+	  dwarf_buf_error (&unit_buf, "unrecognized DWARF version");
+	  goto fail;
+	}
+
+      abbrev_offset = read_offset (&unit_buf, is_dwarf64);
+      if (!read_abbrevs (state, abbrev_offset, dwarf_abbrev, dwarf_abbrev_size,
+			 is_bigendian, error_callback, data, &abbrevs))
+	goto fail;
+
+      addrsize = read_byte (&unit_buf);
+
+      u = ((struct unit *)
+	   backtrace_alloc (state, sizeof *u, error_callback, data));
+      if (u == NULL)
+	goto fail;
+      u->unit_data = unit_buf.buf;
+      u->unit_data_len = unit_buf.left;
+      u->unit_data_offset = unit_buf.buf - unit_data_start;
+      u->version = version;
+      u->is_dwarf64 = is_dwarf64;
+      u->addrsize = addrsize;
+      u->filename = NULL;
+      u->comp_dir = NULL;
+      u->abs_filename = NULL;
+      u->lineoff = 0;
+      u->abbrevs = abbrevs;
+      memset (&abbrevs, 0, sizeof abbrevs);
+
+      /* The actual line number mappings will be read as needed.  */
+      u->lines = NULL;
+      u->lines_count = 0;
+      u->function_addrs = NULL;
+      u->function_addrs_count = 0;
+
+      if (!find_address_ranges (state, base_address, &unit_buf,
+				dwarf_str, dwarf_str_size,
+				dwarf_ranges, dwarf_ranges_size,
+				is_bigendian, error_callback, data,
+				u, addrs))
+	{
+	  free_abbrevs (state, &u->abbrevs, error_callback, data);
+	  backtrace_free (state, u, sizeof *u, error_callback, data);
+	  goto fail;
+	}
+
+      if (unit_buf.reported_underflow)
+	{
+	  free_abbrevs (state, &u->abbrevs, error_callback, data);
+	  backtrace_free (state, u, sizeof *u, error_callback, data);
+	  goto fail;
+	}
+    }
+  if (info.reported_underflow)
+    goto fail;
+
+  return 1;
+
+ fail:
+  free_abbrevs (state, &abbrevs, error_callback, data);
+  free_unit_addrs_vector (state, addrs, error_callback, data);
+  return 0;
+}
+
+/* Add a new mapping to the vector of line mappings that we are
+   building.  Returns 1 on success, 0 on failure.  */
+
+static int
+add_line (struct backtrace_state *state, struct dwarf_data *ddata,
+	  uintptr_t pc, const char *filename, int lineno,
+	  backtrace_error_callback error_callback, void *data,
+	  struct line_vector *vec)
+{
+  struct line *ln;
+
+  /* If we are adding the same mapping, ignore it.  This can happen
+     when using discriminators.  */
+  if (vec->count > 0)
+    {
+      ln = (struct line *) vec->vec.base + (vec->count - 1);
+      if (pc == ln->pc && filename == ln->filename && lineno == ln->lineno)
+	return 1;
+    }
+
+  ln = ((struct line *)
+	backtrace_vector_grow (state, sizeof (struct line), error_callback,
+			       data, &vec->vec));
+  if (ln == NULL)
+    return 0;
+
+  /* Add in the base address here, so that we can look up the PC
+     directly.  */
+  ln->pc = pc + ddata->base_address;
+
+  ln->filename = filename;
+  ln->lineno = lineno;
+  ln->idx = (int)vec->count;
+
+  ++vec->count;
+
+  return 1;
+}
+
+/* Free the line header information.  */
+
+static void
+free_line_header (struct backtrace_state *state, struct line_header *hdr,
+		  backtrace_error_callback error_callback, void *data)
+{
+  if (hdr->dirs_count != 0)
+    backtrace_free (state, hdr->dirs, hdr->dirs_count * sizeof (const char *),
+		    error_callback, data);
+  backtrace_free (state, hdr->filenames,
+		  hdr->filenames_count * sizeof (char *),
+		  error_callback, data);
+}
+
+/* Read the line header.  Return 1 on success, 0 on failure.  */
+
+static int
+read_line_header (struct backtrace_state *state, struct unit *u,
+		  int is_dwarf64, struct dwarf_buf *line_buf,
+		  struct line_header *hdr)
+{
+  uint64_t hdrlen;
+  struct dwarf_buf hdr_buf;
+  const unsigned char *p;
+  const unsigned char *pend;
+  size_t i;
+
+  hdr->version = read_uint16 (line_buf);
+  if (hdr->version < 2 || hdr->version > 4)
+    {
+      dwarf_buf_error (line_buf, "unsupported line number version");
+      return 0;
+    }
+
+  hdrlen = read_offset (line_buf, is_dwarf64);
+
+  hdr_buf = *line_buf;
+  hdr_buf.left = hdrlen;
+
+  if (!advance (line_buf, hdrlen))
+    return 0;
+
+  hdr->min_insn_len = read_byte (&hdr_buf);
+  if (hdr->version < 4)
+    hdr->max_ops_per_insn = 1;
+  else
+    hdr->max_ops_per_insn = read_byte (&hdr_buf);
+
+  /* We don't care about default_is_stmt.  */
+  read_byte (&hdr_buf);
+
+  hdr->line_base = read_sbyte (&hdr_buf);
+  hdr->line_range = read_byte (&hdr_buf);
+
+  hdr->opcode_base = read_byte (&hdr_buf);
+  hdr->opcode_lengths = hdr_buf.buf;
+  if (!advance (&hdr_buf, hdr->opcode_base - 1))
+    return 0;
+
+  /* Count the number of directory entries.  */
+  hdr->dirs_count = 0;
+  p = hdr_buf.buf;
+  pend = p + hdr_buf.left;
+  while (p < pend && *p != '\0')
+    {
+      p += strnlen((const char *) p, pend - p) + 1;
+      ++hdr->dirs_count;
+    }
+
+  hdr->dirs = NULL;
+  if (hdr->dirs_count != 0)
+    {
+      hdr->dirs = ((const char **)
+		   backtrace_alloc (state,
+				    hdr->dirs_count * sizeof (const char *),
+				    line_buf->error_callback, line_buf->data));
+      if (hdr->dirs == NULL)
+	return 0;
+    }
+
+  i = 0;
+  while (*hdr_buf.buf != '\0')
+    {
+      if (hdr_buf.reported_underflow)
+	return 0;
+
+      hdr->dirs[i] = (const char *) hdr_buf.buf;
+      ++i;
+      if (!advance (&hdr_buf,
+		    strnlen ((const char *) hdr_buf.buf, hdr_buf.left) + 1))
+	return 0;
+    }
+  if (!advance (&hdr_buf, 1))
+    return 0;
+
+  /* Count the number of file entries.  */
+  hdr->filenames_count = 0;
+  p = hdr_buf.buf;
+  pend = p + hdr_buf.left;
+  while (p < pend && *p != '\0')
+    {
+      p += strnlen ((const char *) p, pend - p) + 1;
+      p += leb128_len (p);
+      p += leb128_len (p);
+      p += leb128_len (p);
+      ++hdr->filenames_count;
+    }
+
+  hdr->filenames = ((const char **)
+		    backtrace_alloc (state,
+				     hdr->filenames_count * sizeof (char *),
+				     line_buf->error_callback,
+				     line_buf->data));
+  if (hdr->filenames == NULL)
+    return 0;
+  i = 0;
+  while (*hdr_buf.buf != '\0')
+    {
+      const char *filename;
+      uint64_t dir_index;
+
+      if (hdr_buf.reported_underflow)
+	return 0;
+
+      filename = (const char *) hdr_buf.buf;
+      if (!advance (&hdr_buf,
+		    strnlen ((const char *) hdr_buf.buf, hdr_buf.left) + 1))
+	return 0;
+      dir_index = read_uleb128 (&hdr_buf);
+      if (IS_ABSOLUTE_PATH (filename)
+	  || (dir_index == 0 && u->comp_dir == NULL))
+	hdr->filenames[i] = filename;
+      else
+	{
+	  const char *dir;
+	  size_t dir_len;
+	  size_t filename_len;
+	  char *s;
+
+	  if (dir_index == 0)
+	    dir = u->comp_dir;
+	  else if (dir_index - 1 < hdr->dirs_count)
+	    dir = hdr->dirs[dir_index - 1];
+	  else
+	    {
+	      dwarf_buf_error (line_buf,
+			       ("invalid directory index in "
+				"line number program header"));
+	      return 0;
+	    }
+	  dir_len = strlen (dir);
+	  filename_len = strlen (filename);
+	  s = ((char *)
+	       backtrace_alloc (state, dir_len + filename_len + 2,
+				line_buf->error_callback, line_buf->data));
+	  if (s == NULL)
+	    return 0;
+	  memcpy (s, dir, dir_len);
+	  /* FIXME: If we are on a DOS-based file system, and the
+	     directory or the file name use backslashes, then we
+	     should use a backslash here.  */
+	  s[dir_len] = '/';
+	  memcpy (s + dir_len + 1, filename, filename_len + 1);
+	  hdr->filenames[i] = s;
+	}
+
+      /* Ignore the modification time and size.  */
+      read_uleb128 (&hdr_buf);
+      read_uleb128 (&hdr_buf);
+
+      ++i;
+    }
+
+  if (hdr_buf.reported_underflow)
+    return 0;
+
+  return 1;
+}
+
+/* Read the line program, adding line mappings to VEC.  Return 1 on
+   success, 0 on failure.  */
+
+static int
+read_line_program (struct backtrace_state *state, struct dwarf_data *ddata,
+		   struct unit *u, const struct line_header *hdr,
+		   struct dwarf_buf *line_buf, struct line_vector *vec)
+{
+  uint64_t address;
+  unsigned int op_index;
+  const char *reset_filename;
+  const char *filename;
+  int lineno;
+
+  address = 0;
+  op_index = 0;
+  if (hdr->filenames_count > 0)
+    reset_filename = hdr->filenames[0];
+  else
+    reset_filename = "";
+  filename = reset_filename;
+  lineno = 1;
+  while (line_buf->left > 0)
+    {
+      unsigned int op;
+
+      op = read_byte (line_buf);
+      if (op >= hdr->opcode_base)
+	{
+	  unsigned int advance;
+
+	  /* Special opcode.  */
+	  op -= hdr->opcode_base;
+	  advance = op / hdr->line_range;
+	  address += (hdr->min_insn_len * (op_index + advance)
+		      / hdr->max_ops_per_insn);
+	  op_index = (op_index + advance) % hdr->max_ops_per_insn;
+	  lineno += hdr->line_base + (int) (op % hdr->line_range);
+	  add_line (state, ddata, address, filename, lineno,
+		    line_buf->error_callback, line_buf->data, vec);
+	}
+      else if (op == DW_LNS_extended_op)
+	{
+	  uint64_t len;
+
+	  len = read_uleb128 (line_buf);
+	  op = read_byte (line_buf);
+	  switch (op)
+	    {
+	    case DW_LNE_end_sequence:
+	      /* FIXME: Should we mark the high PC here?  It seems
+		 that we already have that information from the
+		 compilation unit.  */
+	      address = 0;
+	      op_index = 0;
+	      filename = reset_filename;
+	      lineno = 1;
+	      break;
+	    case DW_LNE_set_address:
+	      address = read_address (line_buf, u->addrsize);
+	      break;
+	    case DW_LNE_define_file:
+	      {
+		const char *f;
+		unsigned int dir_index;
+
+		f = (const char *) line_buf->buf;
+		if (!advance (line_buf, strnlen (f, line_buf->left) + 1))
+		  return 0;
+		dir_index = (unsigned int)read_uleb128 (line_buf);
+		/* Ignore that time and length.  */
+		read_uleb128 (line_buf);
+		read_uleb128 (line_buf);
+		if (IS_ABSOLUTE_PATH (f))
+		  filename = f;
+		else
+		  {
+		    const char *dir;
+		    size_t dir_len;
+		    size_t f_len;
+		    char *p;
+
+		    if (dir_index == 0)
+		      dir = u->comp_dir;
+		    else if (dir_index - 1 < hdr->dirs_count)
+		      dir = hdr->dirs[dir_index - 1];
+		    else
+		      {
+			dwarf_buf_error (line_buf,
+					 ("invalid directory index "
+					  "in line number program"));
+			return 0;
+		      }
+		    dir_len = strlen (dir);
+		    f_len = strlen (f);
+		    p = ((char *)
+			 backtrace_alloc (state, dir_len + f_len + 2,
+					  line_buf->error_callback,
+					  line_buf->data));
+		    if (p == NULL)
+		      return 0;
+		    memcpy (p, dir, dir_len);
+		    /* FIXME: If we are on a DOS-based file system,
+		       and the directory or the file name use
+		       backslashes, then we should use a backslash
+		       here.  */
+		    p[dir_len] = '/';
+		    memcpy (p + dir_len + 1, f, f_len + 1);
+		    filename = p;
+		  }
+	      }
+	      break;
+	    case DW_LNE_set_discriminator:
+	      /* We don't care about discriminators.  */
+	      read_uleb128 (line_buf);
+	      break;
+	    default:
+	      if (!advance (line_buf, len - 1))
+		return 0;
+	      break;
+	    }
+	}
+      else
+	{
+	  switch (op)
+	    {
+	    case DW_LNS_copy:
+	      add_line (state, ddata, address, filename, lineno,
+			line_buf->error_callback, line_buf->data, vec);
+	      break;
+	    case DW_LNS_advance_pc:
+	      {
+		uint64_t advance;
+
+		advance = read_uleb128 (line_buf);
+		address += (hdr->min_insn_len * (op_index + advance)
+			    / hdr->max_ops_per_insn);
+		op_index = (op_index + advance) % hdr->max_ops_per_insn;
+	      }
+	      break;
+	    case DW_LNS_advance_line:
+	      lineno += (int) read_sleb128 (line_buf);
+	      break;
+	    case DW_LNS_set_file:
+	      {
+		uint64_t fileno;
+
+		fileno = read_uleb128 (line_buf);
+		if (fileno == 0)
+		  filename = "";
+		else
+		  {
+		    if (fileno - 1 >= hdr->filenames_count)
+		      {
+			dwarf_buf_error (line_buf,
+					 ("invalid file number in "
+					  "line number program"));
+			return 0;
+		      }
+		    filename = hdr->filenames[fileno - 1];
+		  }
+	      }
+	      break;
+	    case DW_LNS_set_column:
+	      read_uleb128 (line_buf);
+	      break;
+	    case DW_LNS_negate_stmt:
+	      break;
+	    case DW_LNS_set_basic_block:
+	      break;
+	    case DW_LNS_const_add_pc:
+	      {
+		unsigned int advance;
+
+		op = 255 - hdr->opcode_base;
+		advance = op / hdr->line_range;
+		address += (hdr->min_insn_len * (op_index + advance)
+			    / hdr->max_ops_per_insn);
+		op_index = (op_index + advance) % hdr->max_ops_per_insn;
+	      }
+	      break;
+	    case DW_LNS_fixed_advance_pc:
+	      address += read_uint16 (line_buf);
+	      op_index = 0;
+	      break;
+	    case DW_LNS_set_prologue_end:
+	      break;
+	    case DW_LNS_set_epilogue_begin:
+	      break;
+	    case DW_LNS_set_isa:
+	      read_uleb128 (line_buf);
+	      break;
+	    default:
+	      {
+		unsigned int i;
+
+		for (i = hdr->opcode_lengths[op - 1]; i > 0; --i)
+		  read_uleb128 (line_buf);
+	      }
+	      break;
+	    }
+	}
+    }
+
+  return 1;
+}
+
+/* Read the line number information for a compilation unit.  Returns 1
+   on success, 0 on failure.  */
+
+static int
+read_line_info (struct backtrace_state *state, struct dwarf_data *ddata,
+		backtrace_error_callback error_callback, void *data,
+		struct unit *u, struct line_header *hdr, struct line **lines,
+		size_t *lines_count)
+{
+  struct line_vector vec;
+  struct dwarf_buf line_buf;
+  uint64_t len;
+  int is_dwarf64;
+  struct line *ln;
+
+  memset (&vec.vec, 0, sizeof vec.vec);
+  vec.count = 0;
+
+  memset (hdr, 0, sizeof *hdr);
+
+  if (u->lineoff != (off_t) (size_t) u->lineoff
+      || (size_t) u->lineoff >= ddata->dwarf_line_size)
+    {
+      error_callback (data, "unit line offset out of range", 0);
+      goto fail;
+    }
+
+  line_buf.name = ".debug_line";
+  line_buf.start = ddata->dwarf_line;
+  line_buf.buf = ddata->dwarf_line + u->lineoff;
+  line_buf.left = ddata->dwarf_line_size - u->lineoff;
+  line_buf.is_bigendian = ddata->is_bigendian;
+  line_buf.error_callback = error_callback;
+  line_buf.data = data;
+  line_buf.reported_underflow = 0;
+
+  is_dwarf64 = 0;
+  len = read_uint32 (&line_buf);
+  if (len == 0xffffffff)
+    {
+      len = read_uint64 (&line_buf);
+      is_dwarf64 = 1;
+    }
+  line_buf.left = len;
+
+  if (!read_line_header (state, u, is_dwarf64, &line_buf, hdr))
+    goto fail;
+
+  if (!read_line_program (state, ddata, u, hdr, &line_buf, &vec))
+    goto fail;
+
+  if (line_buf.reported_underflow)
+    goto fail;
+
+  if (vec.count == 0)
+    {
+      /* This is not a failure in the sense of a generating an error,
+	 but it is a failure in that sense that we have no useful
+	 information.  */
+      goto fail;
+    }
+
+  /* Allocate one extra entry at the end.  */
+  ln = ((struct line *)
+	backtrace_vector_grow (state, sizeof (struct line), error_callback,
+			       data, &vec.vec));
+  if (ln == NULL)
+    goto fail;
+  ln->pc = (uintptr_t) -1;
+  ln->filename = NULL;
+  ln->lineno = 0;
+  ln->idx = 0;
+
+  if (!backtrace_vector_release (state, &vec.vec, error_callback, data))
+    goto fail;
+
+  ln = (struct line *) vec.vec.base;
+  backtrace_qsort (ln, vec.count, sizeof (struct line), line_compare);
+
+  *lines = ln;
+  *lines_count = vec.count;
+
+  return 1;
+
+ fail:
+  vec.vec.alc += vec.vec.size;
+  vec.vec.size = 0;
+  backtrace_vector_release (state, &vec.vec, error_callback, data);
+  free_line_header (state, hdr, error_callback, data);
+  *lines = (struct line *) (uintptr_t) -1;
+  *lines_count = 0;
+  return 0;
+}
+
+/* Read the name of a function from a DIE referenced by a
+   DW_AT_abstract_origin or DW_AT_specification tag.  OFFSET is within
+   the same compilation unit.  */
+
+static const char *
+read_referenced_name (struct dwarf_data *ddata, struct unit *u,
+		      uint64_t offset, backtrace_error_callback error_callback,
+		      void *data)
+{
+  struct dwarf_buf unit_buf;
+  uint64_t code;
+  const struct abbrev *abbrev;
+  const char *ret;
+  size_t i;
+
+  /* OFFSET is from the start of the data for this compilation unit.
+     U->unit_data is the data, but it starts U->unit_data_offset bytes
+     from the beginning.  */
+
+  if (offset < u->unit_data_offset
+      || offset - u->unit_data_offset >= u->unit_data_len)
+    {
+      error_callback (data,
+		      "abstract origin or specification out of range",
+		      0);
+      return NULL;
+    }
+
+  offset -= u->unit_data_offset;
+
+  unit_buf.name = ".debug_info";
+  unit_buf.start = ddata->dwarf_info;
+  unit_buf.buf = u->unit_data + offset;
+  unit_buf.left = u->unit_data_len - offset;
+  unit_buf.is_bigendian = ddata->is_bigendian;
+  unit_buf.error_callback = error_callback;
+  unit_buf.data = data;
+  unit_buf.reported_underflow = 0;
+
+  code = read_uleb128 (&unit_buf);
+  if (code == 0)
+    {
+      dwarf_buf_error (&unit_buf, "invalid abstract origin or specification");
+      return NULL;
+    }
+
+  abbrev = lookup_abbrev (&u->abbrevs, code, error_callback, data);
+  if (abbrev == NULL)
+    return NULL;
+
+  ret = NULL;
+  for (i = 0; i < abbrev->num_attrs; ++i)
+    {
+      struct attr_val val;
+
+      if (!read_attribute (abbrev->attrs[i].form, &unit_buf,
+			   u->is_dwarf64, u->version, u->addrsize,
+			   ddata->dwarf_str, ddata->dwarf_str_size,
+			   &val))
+	return NULL;
+
+      switch (abbrev->attrs[i].name)
+	{
+	case DW_AT_name:
+	  /* We prefer the linkage name if get one.  */
+	  if (val.encoding == ATTR_VAL_STRING)
+	    ret = val.u.string;
+	  break;
+
+	case DW_AT_linkage_name:
+	case DW_AT_MIPS_linkage_name:
+	  if (val.encoding == ATTR_VAL_STRING)
+	    return val.u.string;
+	  break;
+
+	case DW_AT_specification:
+	  if (abbrev->attrs[i].form == DW_FORM_ref_addr
+	      || abbrev->attrs[i].form == DW_FORM_ref_sig8)
+	    {
+	      /* This refers to a specification defined in some other
+		 compilation unit.  We can handle this case if we
+		 must, but it's harder.  */
+	      break;
+	    }
+	  if (val.encoding == ATTR_VAL_UINT
+	      || val.encoding == ATTR_VAL_REF_UNIT)
+	    {
+	      const char *name;
+
+	      name = read_referenced_name (ddata, u, val.u.uint,
+					   error_callback, data);
+	      if (name != NULL)
+		ret = name;
+	    }
+	  break;
+
+	default:
+	  break;
+	}
+    }
+
+  return ret;
+}
+
+/* Add a single range to U that maps to function.  Returns 1 on
+   success, 0 on error.  */
+
+static int
+add_function_range (struct backtrace_state *state, struct dwarf_data *ddata,
+		    struct function *function, uint64_t lowpc, uint64_t highpc,
+		    backtrace_error_callback error_callback,
+		    void *data, struct function_vector *vec)
+{
+  struct function_addrs *p;
+
+  /* Add in the base address here, so that we can look up the PC
+     directly.  */
+  lowpc += ddata->base_address;
+  highpc += ddata->base_address;
+
+  if (vec->count > 0)
+    {
+      p = (struct function_addrs *) vec->vec.base + vec->count - 1;
+      if ((lowpc == p->high || lowpc == p->high + 1)
+	  && function == p->function)
+	{
+	  if (highpc > p->high)
+	    p->high = highpc;
+	  return 1;
+	}
+    }
+
+  p = ((struct function_addrs *)
+       backtrace_vector_grow (state, sizeof (struct function_addrs),
+			      error_callback, data, &vec->vec));
+  if (p == NULL)
+    return 0;
+
+  p->low = lowpc;
+  p->high = highpc;
+  p->function = function;
+  ++vec->count;
+  return 1;
+}
+
+/* Add PC ranges to U that map to FUNCTION.  Returns 1 on success, 0
+   on error.  */
+
+static int
+add_function_ranges (struct backtrace_state *state, struct dwarf_data *ddata,
+		     struct unit *u, struct function *function,
+		     uint64_t ranges, uint64_t base,
+		     backtrace_error_callback error_callback, void *data,
+		     struct function_vector *vec)
+{
+  struct dwarf_buf ranges_buf;
+
+  if (ranges >= ddata->dwarf_ranges_size)
+    {
+      error_callback (data, "function ranges offset out of range", 0);
+      return 0;
+    }
+
+  ranges_buf.name = ".debug_ranges";
+  ranges_buf.start = ddata->dwarf_ranges;
+  ranges_buf.buf = ddata->dwarf_ranges + ranges;
+  ranges_buf.left = ddata->dwarf_ranges_size - ranges;
+  ranges_buf.is_bigendian = ddata->is_bigendian;
+  ranges_buf.error_callback = error_callback;
+  ranges_buf.data = data;
+  ranges_buf.reported_underflow = 0;
+
+  while (1)
+    {
+      uint64_t low;
+      uint64_t high;
+
+      if (ranges_buf.reported_underflow)
+	return 0;
+
+      low = read_address (&ranges_buf, u->addrsize);
+      high = read_address (&ranges_buf, u->addrsize);
+
+      if (low == 0 && high == 0)
+	break;
+
+      if (is_highest_address (low, u->addrsize))
+	base = high;
+      else
+	{
+	  if (!add_function_range (state, ddata, function, low + base,
+				   high + base, error_callback, data, vec))
+	    return 0;
+	}
+    }
+
+  if (ranges_buf.reported_underflow)
+    return 0;
+
+  return 1;
+}
+
+/* Read one entry plus all its children.  Add function addresses to
+   VEC.  Returns 1 on success, 0 on error.  */
+
+static int
+read_function_entry (struct backtrace_state *state, struct dwarf_data *ddata,
+		     struct unit *u, uint64_t base, struct dwarf_buf *unit_buf,
+		     const struct line_header *lhdr,
+		     backtrace_error_callback error_callback, void *data,
+		     struct function_vector *vec_function,
+		     struct function_vector *vec_inlined)
+{
+  while (unit_buf->left > 0)
+    {
+      uint64_t code;
+      const struct abbrev *abbrev;
+      int is_function;
+      struct function *function;
+      struct function_vector *vec;
+      size_t i;
+      uint64_t lowpc;
+      int have_lowpc;
+      uint64_t highpc;
+      int have_highpc;
+      int highpc_is_relative;
+      uint64_t ranges;
+      int have_ranges;
+
+      code = read_uleb128 (unit_buf);
+      if (code == 0)
+	return 1;
+
+      abbrev = lookup_abbrev (&u->abbrevs, code, error_callback, data);
+      if (abbrev == NULL)
+	return 0;
+
+      is_function = (abbrev->tag == DW_TAG_subprogram
+		     || abbrev->tag == DW_TAG_entry_point
+		     || abbrev->tag == DW_TAG_inlined_subroutine);
+
+      if (abbrev->tag == DW_TAG_inlined_subroutine)
+	vec = vec_inlined;
+      else
+	vec = vec_function;
+
+      function = NULL;
+      if (is_function)
+	{
+	  function = ((struct function *)
+		      backtrace_alloc (state, sizeof *function,
+				       error_callback, data));
+	  if (function == NULL)
+	    return 0;
+	  memset (function, 0, sizeof *function);
+	}
+
+      lowpc = 0;
+      have_lowpc = 0;
+      highpc = 0;
+      have_highpc = 0;
+      highpc_is_relative = 0;
+      ranges = 0;
+      have_ranges = 0;
+      for (i = 0; i < abbrev->num_attrs; ++i)
+	{
+	  struct attr_val val;
+
+	  if (!read_attribute (abbrev->attrs[i].form, unit_buf,
+			       u->is_dwarf64, u->version, u->addrsize,
+			       ddata->dwarf_str, ddata->dwarf_str_size,
+			       &val))
+	    return 0;
+
+	  /* The compile unit sets the base address for any address
+	     ranges in the function entries.  */
+	  if (abbrev->tag == DW_TAG_compile_unit
+	      && abbrev->attrs[i].name == DW_AT_low_pc
+	      && val.encoding == ATTR_VAL_ADDRESS)
+	    base = val.u.uint;
+
+	  if (is_function)
+	    {
+	      switch (abbrev->attrs[i].name)
+		{
+		case DW_AT_call_file:
+		  if (val.encoding == ATTR_VAL_UINT)
+		    {
+		      if (val.u.uint == 0)
+			function->caller_filename = "";
+		      else
+			{
+			  if (val.u.uint - 1 >= lhdr->filenames_count)
+			    {
+			      dwarf_buf_error (unit_buf,
+					       ("invalid file number in "
+						"DW_AT_call_file attribute"));
+			      return 0;
+			    }
+			  function->caller_filename =
+			    lhdr->filenames[val.u.uint - 1];
+			}
+		    }
+		  break;
+
+		case DW_AT_call_line:
+		  if (val.encoding == ATTR_VAL_UINT)
+		    function->caller_lineno = (int)val.u.uint;
+		  break;
+
+		case DW_AT_abstract_origin:
+		case DW_AT_specification:
+		  if (abbrev->attrs[i].form == DW_FORM_ref_addr
+		      || abbrev->attrs[i].form == DW_FORM_ref_sig8)
+		    {
+		      /* This refers to an abstract origin defined in
+			 some other compilation unit.  We can handle
+			 this case if we must, but it's harder.  */
+		      break;
+		    }
+		  if (val.encoding == ATTR_VAL_UINT
+		      || val.encoding == ATTR_VAL_REF_UNIT)
+		    {
+		      const char *name;
+
+		      name = read_referenced_name (ddata, u, val.u.uint,
+						   error_callback, data);
+		      if (name != NULL)
+			function->name = name;
+		    }
+		  break;
+
+		case DW_AT_name:
+		  if (val.encoding == ATTR_VAL_STRING)
+		    {
+		      /* Don't override a name we found in some other
+			 way, as it will normally be more
+			 useful--e.g., this name is normally not
+			 mangled.  */
+		      if (function->name == NULL)
+			function->name = val.u.string;
+		    }
+		  break;
+
+		case DW_AT_linkage_name:
+		case DW_AT_MIPS_linkage_name:
+		  if (val.encoding == ATTR_VAL_STRING)
+		    function->name = val.u.string;
+		  break;
+
+		case DW_AT_low_pc:
+		  if (val.encoding == ATTR_VAL_ADDRESS)
+		    {
+		      lowpc = val.u.uint;
+		      have_lowpc = 1;
+		    }
+		  break;
+
+		case DW_AT_high_pc:
+		  if (val.encoding == ATTR_VAL_ADDRESS)
+		    {
+		      highpc = val.u.uint;
+		      have_highpc = 1;
+		    }
+		  else if (val.encoding == ATTR_VAL_UINT)
+		    {
+		      highpc = val.u.uint;
+		      have_highpc = 1;
+		      highpc_is_relative = 1;
+		    }
+		  break;
+
+		case DW_AT_ranges:
+		  if (val.encoding == ATTR_VAL_UINT
+		      || val.encoding == ATTR_VAL_REF_SECTION)
+		    {
+		      ranges = val.u.uint;
+		      have_ranges = 1;
+		    }
+		  break;
+
+		default:
+		  break;
+		}
+	    }
+	}
+
+      /* If we couldn't find a name for the function, we have no use
+	 for it.  */
+      if (is_function && function->name == NULL)
+	{
+	  backtrace_free (state, function, sizeof *function,
+			  error_callback, data);
+	  is_function = 0;
+	}
+
+      if (is_function)
+	{
+	  if (have_ranges)
+	    {
+	      if (!add_function_ranges (state, ddata, u, function, ranges,
+					base, error_callback, data, vec))
+		return 0;
+	    }
+	  else if (have_lowpc && have_highpc)
+	    {
+	      if (highpc_is_relative)
+		highpc += lowpc;
+	      if (!add_function_range (state, ddata, function, lowpc, highpc,
+				       error_callback, data, vec))
+		return 0;
+	    }
+	  else
+	    {
+	      backtrace_free (state, function, sizeof *function,
+			      error_callback, data);
+	      is_function = 0;
+	    }
+	}
+
+      if (abbrev->has_children)
+	{
+	  if (!is_function)
+	    {
+	      if (!read_function_entry (state, ddata, u, base, unit_buf, lhdr,
+					error_callback, data, vec_function,
+					vec_inlined))
+		return 0;
+	    }
+	  else
+	    {
+	      struct function_vector fvec;
+
+	      /* Gather any information for inlined functions in
+		 FVEC.  */
+
+	      memset (&fvec, 0, sizeof fvec);
+
+	      if (!read_function_entry (state, ddata, u, base, unit_buf, lhdr,
+					error_callback, data, vec_function,
+					&fvec))
+		return 0;
+
+	      if (fvec.count > 0)
+		{
+		  struct function_addrs *faddrs;
+
+		  if (!backtrace_vector_release (state, &fvec.vec,
+						 error_callback, data))
+		    return 0;
+
+		  faddrs = (struct function_addrs *) fvec.vec.base;
+		  backtrace_qsort (faddrs, fvec.count,
+				   sizeof (struct function_addrs),
+				   function_addrs_compare);
+
+		  function->function_addrs = faddrs;
+		  function->function_addrs_count = fvec.count;
+		}
+	    }
+	}
+    }
+
+  return 1;
+}
+
+/* Read function name information for a compilation unit.  We look
+   through the whole unit looking for function tags.  */
+
+static void
+read_function_info (struct backtrace_state *state, struct dwarf_data *ddata,
+		    const struct line_header *lhdr,
+		    backtrace_error_callback error_callback, void *data,
+		    struct unit *u, struct function_vector *fvec,
+		    struct function_addrs **ret_addrs,
+		    size_t *ret_addrs_count)
+{
+  struct function_vector lvec;
+  struct function_vector *pfvec;
+  struct dwarf_buf unit_buf;
+  struct function_addrs *addrs;
+  size_t addrs_count;
+
+  /* Use FVEC if it is not NULL.  Otherwise use our own vector.  */
+  if (fvec != NULL)
+    pfvec = fvec;
+  else
+    {
+      memset (&lvec, 0, sizeof lvec);
+      pfvec = &lvec;
+    }
+
+  unit_buf.name = ".debug_info";
+  unit_buf.start = ddata->dwarf_info;
+  unit_buf.buf = u->unit_data;
+  unit_buf.left = u->unit_data_len;
+  unit_buf.is_bigendian = ddata->is_bigendian;
+  unit_buf.error_callback = error_callback;
+  unit_buf.data = data;
+  unit_buf.reported_underflow = 0;
+
+  while (unit_buf.left > 0)
+    {
+      if (!read_function_entry (state, ddata, u, 0, &unit_buf, lhdr,
+				error_callback, data, pfvec, pfvec))
+	return;
+    }
+
+  if (pfvec->count == 0)
+    return;
+
+  addrs_count = pfvec->count;
+
+  if (fvec == NULL)
+    {
+      if (!backtrace_vector_release (state, &lvec.vec, error_callback, data))
+	return;
+      addrs = (struct function_addrs *) pfvec->vec.base;
+    }
+  else
+    {
+      /* Finish this list of addresses, but leave the remaining space in
+	 the vector available for the next function unit.  */
+      addrs = ((struct function_addrs *)
+	       backtrace_vector_finish (state, &fvec->vec,
+					error_callback, data));
+      if (addrs == NULL)
+	return;
+      fvec->count = 0;
+    }
+
+  backtrace_qsort (addrs, addrs_count, sizeof (struct function_addrs),
+		   function_addrs_compare);
+
+  *ret_addrs = addrs;
+  *ret_addrs_count = addrs_count;
+}
+
+/* See if PC is inlined in FUNCTION.  If it is, print out the inlined
+   information, and update FILENAME and LINENO for the caller.
+   Returns whatever CALLBACK returns, or 0 to keep going.  */
+
+static int
+report_inlined_functions (uintptr_t pc, struct function *function,
+			  backtrace_full_callback callback, void *data,
+			  const char **filename, int *lineno)
+{
+  struct function_addrs *function_addrs;
+  struct function *inlined;
+  int ret;
+
+  if (function->function_addrs_count == 0)
+    return 0;
+
+  function_addrs = ((struct function_addrs *)
+		    bsearch (&pc, function->function_addrs,
+			     function->function_addrs_count,
+			     sizeof (struct function_addrs),
+			     function_addrs_search));
+  if (function_addrs == NULL)
+    return 0;
+
+  while (((size_t) (function_addrs - function->function_addrs) + 1
+	  < function->function_addrs_count)
+	 && pc >= (function_addrs + 1)->low
+	 && pc < (function_addrs + 1)->high)
+    ++function_addrs;
+
+  /* We found an inlined call.  */
+
+  inlined = function_addrs->function;
+
+  /* Report any calls inlined into this one.  */
+  ret = report_inlined_functions (pc, inlined, callback, data,
+				  filename, lineno);
+  if (ret != 0)
+    return ret;
+
+  /* Report this inlined call.  */
+  ret = callback (data, pc, *filename, *lineno, inlined->name);
+  if (ret != 0)
+    return ret;
+
+  /* Our caller will report the caller of the inlined function; tell
+     it the appropriate filename and line number.  */
+  *filename = inlined->caller_filename;
+  *lineno = inlined->caller_lineno;
+
+  return 0;
+}
+
+/* Look for a PC in the DWARF mapping for one module.  On success,
+   call CALLBACK and return whatever it returns.  On error, call
+   ERROR_CALLBACK and return 0.  Sets *FOUND to 1 if the PC is found,
+   0 if not.  */
+
+static int
+dwarf_lookup_pc (struct backtrace_state *state, struct dwarf_data *ddata,
+		 uintptr_t pc, backtrace_full_callback callback,
+		 backtrace_error_callback error_callback, void *data,
+		 int *found)
+{
+  struct unit_addrs *entry;
+  struct unit *u;
+  int new_data;
+  struct line *lines;
+  struct line *ln;
+  struct function_addrs *function_addrs;
+  struct function *function;
+  const char *filename;
+  int lineno;
+  int ret;
+
+  *found = 1;
+
+  /* Find an address range that includes PC.  */
+  entry = bsearch (&pc, ddata->addrs, ddata->addrs_count,
+		   sizeof (struct unit_addrs), unit_addrs_search);
+
+  if (entry == NULL)
+    {
+      *found = 0;
+      return 0;
+    }
+
+  /* If there are multiple ranges that contain PC, use the last one,
+     in order to produce predictable results.  If we assume that all
+     ranges are properly nested, then the last range will be the
+     smallest one.  */
+  while ((size_t) (entry - ddata->addrs) + 1 < ddata->addrs_count
+	 && pc >= (entry + 1)->low
+	 && pc < (entry + 1)->high)
+    ++entry;
+
+  /* We need the lines, lines_count, function_addrs,
+     function_addrs_count fields of u.  If they are not set, we need
+     to set them.  When running in threaded mode, we need to allow for
+     the possibility that some other thread is setting them
+     simultaneously.  */
+
+  u = entry->u;
+  lines = u->lines;
+
+  /* Skip units with no useful line number information by walking
+     backward.  Useless line number information is marked by setting
+     lines == -1.  */
+  while (entry > ddata->addrs
+	 && pc >= (entry - 1)->low
+	 && pc < (entry - 1)->high)
+    {
+      if (state->threaded)
+	lines = (struct line *) backtrace_atomic_load_pointer (&u->lines);
+
+      if (lines != (struct line *) (uintptr_t) -1)
+	break;
+
+      --entry;
+
+      u = entry->u;
+      lines = u->lines;
+    }
+
+  if (state->threaded)
+    lines = backtrace_atomic_load_pointer (&u->lines);
+
+  new_data = 0;
+  if (lines == NULL)
+    {
+      size_t function_addrs_count;
+      struct line_header lhdr;
+      size_t count;
+
+      /* We have never read the line information for this unit.  Read
+	 it now.  */
+
+      function_addrs = NULL;
+      function_addrs_count = 0;
+      if (read_line_info (state, ddata, error_callback, data, entry->u, &lhdr,
+			  &lines, &count))
+	{
+	  struct function_vector *pfvec;
+
+	  /* If not threaded, reuse DDATA->FVEC for better memory
+	     consumption.  */
+	  if (state->threaded)
+	    pfvec = NULL;
+	  else
+	    pfvec = &ddata->fvec;
+	  read_function_info (state, ddata, &lhdr, error_callback, data,
+			      entry->u, pfvec, &function_addrs,
+			      &function_addrs_count);
+	  free_line_header (state, &lhdr, error_callback, data);
+	  new_data = 1;
+	}
+
+      /* Atomically store the information we just read into the unit.
+	 If another thread is simultaneously writing, it presumably
+	 read the same information, and we don't care which one we
+	 wind up with; we just leak the other one.  We do have to
+	 write the lines field last, so that the acquire-loads above
+	 ensure that the other fields are set.  */
+
+      if (!state->threaded)
+	{
+	  u->lines_count = count;
+	  u->function_addrs = function_addrs;
+	  u->function_addrs_count = function_addrs_count;
+	  u->lines = lines;
+	}
+      else
+	{
+	  backtrace_atomic_store_size_t (&u->lines_count, count);
+	  backtrace_atomic_store_pointer (&u->function_addrs, function_addrs);
+	  backtrace_atomic_store_size_t (&u->function_addrs_count,
+					 function_addrs_count);
+	  backtrace_atomic_store_pointer (&u->lines, lines);
+	}
+    }
+
+  /* Now all fields of U have been initialized.  */
+
+  if (lines == (struct line *) (uintptr_t) -1)
+    {
+      /* If reading the line number information failed in some way,
+	 try again to see if there is a better compilation unit for
+	 this PC.  */
+      if (new_data)
+	return dwarf_lookup_pc (state, ddata, pc, callback, error_callback,
+				data, found);
+      return callback (data, pc, NULL, 0, NULL);
+    }
+
+  /* Search for PC within this unit.  */
+
+  ln = (struct line *) bsearch (&pc, lines, entry->u->lines_count,
+				sizeof (struct line), line_search);
+  if (ln == NULL)
+    {
+      /* The PC is between the low_pc and high_pc attributes of the
+	 compilation unit, but no entry in the line table covers it.
+	 This implies that the start of the compilation unit has no
+	 line number information.  */
+
+      if (entry->u->abs_filename == NULL)
+	{
+	  const char *filename1;
+
+	  filename1 = entry->u->filename;
+	  if (filename1 != NULL
+	      && !IS_ABSOLUTE_PATH (filename1)
+	      && entry->u->comp_dir != NULL)
+	    {
+	      size_t filename_len;
+	      const char *dir;
+	      size_t dir_len;
+	      char *s;
+
+	      filename_len = strlen (filename1);
+	      dir = entry->u->comp_dir;
+	      dir_len = strlen (dir);
+	      s = (char *) backtrace_alloc (state, dir_len + filename_len + 2,
+					    error_callback, data);
+	      if (s == NULL)
+		{
+		  *found = 0;
+		  return 0;
+		}
+	      memcpy (s, dir, dir_len);
+	      /* FIXME: Should use backslash if DOS file system.  */
+	      s[dir_len] = '/';
+	      memcpy (s + dir_len + 1, filename1, filename_len + 1);
+	      filename1 = s;
+	    }
+	  entry->u->abs_filename = filename1;
+	}
+
+      return callback (data, pc, entry->u->abs_filename, 0, NULL);
+    }
+
+  /* Search for function name within this unit.  */
+
+  if (entry->u->function_addrs_count == 0)
+    return callback (data, pc, ln->filename, ln->lineno, NULL);
+
+  function_addrs = ((struct function_addrs *)
+		    bsearch (&pc, entry->u->function_addrs,
+			     entry->u->function_addrs_count,
+			     sizeof (struct function_addrs),
+			     function_addrs_search));
+  if (function_addrs == NULL)
+    return callback (data, pc, ln->filename, ln->lineno, NULL);
+
+  /* If there are multiple function ranges that contain PC, use the
+     last one, in order to produce predictable results.  */
+
+  while (((size_t) (function_addrs - entry->u->function_addrs + 1)
+	  < entry->u->function_addrs_count)
+	 && pc >= (function_addrs + 1)->low
+	 && pc < (function_addrs + 1)->high)
+    ++function_addrs;
+
+  function = function_addrs->function;
+
+  filename = ln->filename;
+  lineno = ln->lineno;
+
+  ret = report_inlined_functions (pc, function, callback, data,
+				  &filename, &lineno);
+  if (ret != 0)
+    return ret;
+
+  return callback (data, pc, filename, lineno, function->name);
+}
+
+
+/* Return the file/line information for a PC using the DWARF mapping
+   we built earlier.  */
+
+static int
+dwarf_fileline (struct backtrace_state *state, uintptr_t pc,
+		backtrace_full_callback callback,
+		backtrace_error_callback error_callback, void *data)
+{
+  struct dwarf_data *ddata;
+  int found;
+  int ret;
+
+  if (!state->threaded)
+    {
+      for (ddata = (struct dwarf_data *) state->fileline_data;
+	   ddata != NULL;
+	   ddata = ddata->next)
+	{
+	  ret = dwarf_lookup_pc (state, ddata, pc, callback, error_callback,
+				 data, &found);
+	  if (ret != 0 || found)
+	    return ret;
+	}
+    }
+  else
+    {
+      struct dwarf_data **pp;
+
+      pp = (struct dwarf_data **) (void *) &state->fileline_data;
+      while (1)
+	{
+	  ddata = backtrace_atomic_load_pointer (pp);
+	  if (ddata == NULL)
+	    break;
+
+	  ret = dwarf_lookup_pc (state, ddata, pc, callback, error_callback,
+				 data, &found);
+	  if (ret != 0 || found)
+	    return ret;
+
+	  pp = &ddata->next;
+	}
+    }
+
+  /* FIXME: See if any libraries have been dlopen'ed.  */
+
+  return callback (data, pc, NULL, 0, NULL);
+}
+
+/* Initialize our data structures from the DWARF debug info for a
+   file.  Return NULL on failure.  */
+
+static struct dwarf_data *
+build_dwarf_data (struct backtrace_state *state,
+		  uintptr_t base_address,
+		  const unsigned char *dwarf_info,
+		  size_t dwarf_info_size,
+		  const unsigned char *dwarf_line,
+		  size_t dwarf_line_size,
+		  const unsigned char *dwarf_abbrev,
+		  size_t dwarf_abbrev_size,
+		  const unsigned char *dwarf_ranges,
+		  size_t dwarf_ranges_size,
+		  const unsigned char *dwarf_str,
+		  size_t dwarf_str_size,
+		  int is_bigendian,
+		  backtrace_error_callback error_callback,
+		  void *data)
+{
+  struct unit_addrs_vector addrs_vec;
+  struct unit_addrs *addrs;
+  size_t addrs_count;
+  struct dwarf_data *fdata;
+
+  if (!build_address_map (state, base_address, dwarf_info, dwarf_info_size,
+			  dwarf_abbrev, dwarf_abbrev_size, dwarf_ranges,
+			  dwarf_ranges_size, dwarf_str, dwarf_str_size,
+			  is_bigendian, error_callback, data, &addrs_vec))
+    return NULL;
+
+  if (!backtrace_vector_release (state, &addrs_vec.vec, error_callback, data))
+    return NULL;
+  addrs = (struct unit_addrs *) addrs_vec.vec.base;
+  addrs_count = addrs_vec.count;
+  backtrace_qsort (addrs, addrs_count, sizeof (struct unit_addrs),
+		   unit_addrs_compare);
+
+  fdata = ((struct dwarf_data *)
+	   backtrace_alloc (state, sizeof (struct dwarf_data),
+			    error_callback, data));
+  if (fdata == NULL)
+    return NULL;
+
+  fdata->next = NULL;
+  fdata->base_address = base_address;
+  fdata->addrs = addrs;
+  fdata->addrs_count = addrs_count;
+  fdata->dwarf_info = dwarf_info;
+  fdata->dwarf_info_size = dwarf_info_size;
+  fdata->dwarf_line = dwarf_line;
+  fdata->dwarf_line_size = dwarf_line_size;
+  fdata->dwarf_ranges = dwarf_ranges;
+  fdata->dwarf_ranges_size = dwarf_ranges_size;
+  fdata->dwarf_str = dwarf_str;
+  fdata->dwarf_str_size = dwarf_str_size;
+  fdata->is_bigendian = is_bigendian;
+  memset (&fdata->fvec, 0, sizeof fdata->fvec);
+
+  return fdata;
+}
+
+/* Build our data structures from the DWARF sections for a module.
+   Set FILELINE_FN and STATE->FILELINE_DATA.  Return 1 on success, 0
+   on failure.  */
+
+int
+backtrace_dwarf_add (struct backtrace_state *state,
+		     uintptr_t base_address,
+		     const unsigned char *dwarf_info,
+		     size_t dwarf_info_size,
+		     const unsigned char *dwarf_line,
+		     size_t dwarf_line_size,
+		     const unsigned char *dwarf_abbrev,
+		     size_t dwarf_abbrev_size,
+		     const unsigned char *dwarf_ranges,
+		     size_t dwarf_ranges_size,
+		     const unsigned char *dwarf_str,
+		     size_t dwarf_str_size,
+		     int is_bigendian,
+		     backtrace_error_callback error_callback,
+		     void *data, fileline *fileline_fn)
+{
+  struct dwarf_data *fdata;
+
+  fdata = build_dwarf_data (state, base_address, dwarf_info, dwarf_info_size,
+			    dwarf_line, dwarf_line_size, dwarf_abbrev,
+			    dwarf_abbrev_size, dwarf_ranges, dwarf_ranges_size,
+			    dwarf_str, dwarf_str_size, is_bigendian,
+			    error_callback, data);
+  if (fdata == NULL)
+    return 0;
+
+  if (!state->threaded)
+    {
+      struct dwarf_data **pp;
+
+      for (pp = (struct dwarf_data **) (void *) &state->fileline_data;
+	   *pp != NULL;
+	   pp = &(*pp)->next)
+	;
+      *pp = fdata;
+    }
+  else
+    {
+      while (1)
+	{
+	  struct dwarf_data **pp;
+
+	  pp = (struct dwarf_data **) (void *) &state->fileline_data;
+
+	  while (1)
+	    {
+	      struct dwarf_data *p;
+
+	      p = backtrace_atomic_load_pointer (pp);
+
+	      if (p == NULL)
+		break;
+
+	      pp = &p->next;
+	    }
+
+	  if (__sync_bool_compare_and_swap (pp, NULL, fdata))
+	    break;
+	}
+    }
+
+  *fileline_fn = dwarf_fileline;
+
+  return 1;
+}