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/* DWARF 2 location expression support for GDB.

   Copyright (C) 2003, 2005, 2007, 2008 Free Software Foundation, Inc.

   Contributed by Daniel Jacobowitz, MontaVista Software, Inc.

   This file is part of GDB.

   This program 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; either version 3 of the License, or

   (at your option) any later version.

   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"

#include "ui-out.h"

#include "value.h"

#include "frame.h"

#include "gdbcore.h"

#include "target.h"

#include "inferior.h"

#include "ax.h"

#include "ax-gdb.h"

#include "regcache.h"

#include "objfiles.h"

#include "exceptions.h"

#include "elf/dwarf2.h"

#include "dwarf2expr.h"

#include "dwarf2loc.h"

#include "gdb_string.h"

#include "gdb_assert.h"

/* A helper function for dealing with location lists.  Given a

   symbol baton (BATON) and a pc value (PC), find the appropriate

   location expression, set *LOCEXPR_LENGTH, and return a pointer

   to the beginning of the expression.  Returns NULL on failure.

   For now, only return the first matching location expression; there

   can be more than one in the list.  */

static gdb_byte *

find_location_expression (struct dwarf2_loclist_baton *baton,

                          size_t *locexpr_length, CORE_ADDR pc)

{

  CORE_ADDR low, high;

  gdb_byte *loc_ptr, *buf_end;

  int length;

  unsigned int addr_size = gdbarch_addr_bit (current_gdbarch) / TARGET_CHAR_BIT;

  CORE_ADDR base_mask = ~(~(CORE_ADDR)1 << (addr_size * 8 - 1));

  /* Adjust base_address for relocatable objects.  */

  CORE_ADDR base_offset = ANOFFSET (baton->objfile->section_offsets,

                                    SECT_OFF_TEXT (baton->objfile));

  CORE_ADDR base_address = baton->base_address + base_offset;

  loc_ptr = baton->data;

  buf_end = baton->data + baton->size;

  while (1)

    {

      low = dwarf2_read_address (loc_ptr, buf_end, &length);

      loc_ptr += length;

      high = dwarf2_read_address (loc_ptr, buf_end, &length);

      loc_ptr += length;

      /* An end-of-list entry.  */

      if (low == 0 && high == 0)

        return NULL;

      /* A base-address-selection entry.  */

      if ((low & base_mask) == base_mask)

        {

          base_address = high;

          continue;

        }

      /* Otherwise, a location expression entry.  */

      low += base_address;

      high += base_address;

      length = extract_unsigned_integer (loc_ptr, 2);

      loc_ptr += 2;

      if (pc >= low && pc < high)

        {

          *locexpr_length = length;

          return loc_ptr;

        }

      loc_ptr += length;

    }

}

/* This is the baton used when performing dwarf2 expression

   evaluation.  */

struct dwarf_expr_baton

{

  struct frame_info *frame;

  struct objfile *objfile;

};

/* Helper functions for dwarf2_evaluate_loc_desc.  */

/* Using the frame specified in BATON, return the value of register

   REGNUM, treated as a pointer.  */

static CORE_ADDR

dwarf_expr_read_reg (void *baton, int dwarf_regnum)

{

  struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;

  CORE_ADDR result;

  int regnum;

  regnum = gdbarch_dwarf2_reg_to_regnum (current_gdbarch, dwarf_regnum);

  result = address_from_register (builtin_type_void_data_ptr,

                                  regnum, debaton->frame);

  return result;

}

/* Read memory at ADDR (length LEN) into BUF.  */

static void

dwarf_expr_read_mem (void *baton, gdb_byte *buf, CORE_ADDR addr, size_t len)

{

  read_memory (addr, buf, len);

}

/* Using the frame specified in BATON, find the location expression

   describing the frame base.  Return a pointer to it in START and

   its length in LENGTH.  */

static void

dwarf_expr_frame_base (void *baton, gdb_byte **start, size_t * length)

{

  /* FIXME: cagney/2003-03-26: This code should be using

     get_frame_base_address(), and then implement a dwarf2 specific

     this_base method.  */

  struct symbol *framefunc;

  struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;

  framefunc = get_frame_function (debaton->frame);

  /* If we found a frame-relative symbol then it was certainly within

     some function associated with a frame. If we can't find the frame,

     something has gone wrong.  */

  gdb_assert (framefunc != NULL);

  if (SYMBOL_OPS (framefunc) == &dwarf2_loclist_funcs)

    {

      struct dwarf2_loclist_baton *symbaton;

      struct frame_info *frame = debaton->frame;

      symbaton = SYMBOL_LOCATION_BATON (framefunc);

      *start = find_location_expression (symbaton, length,

                                         get_frame_address_in_block (frame));

    }

  else

    {

      struct dwarf2_locexpr_baton *symbaton;

      symbaton = SYMBOL_LOCATION_BATON (framefunc);

      *length = symbaton->size;

      *start = symbaton->data;

    }

  if (*start == NULL)

    error (_("Could not find the frame base for \"%s\"."),

           SYMBOL_NATURAL_NAME (framefunc));

}

/* Using the objfile specified in BATON, find the address for the

   current thread's thread-local storage with offset OFFSET.  */

static CORE_ADDR

dwarf_expr_tls_address (void *baton, CORE_ADDR offset)

{

  struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;

  return target_translate_tls_address (debaton->objfile, offset);

}

/* Evaluate a location description, starting at DATA and with length

   SIZE, to find the current location of variable VAR in the context

   of FRAME.  */

static struct value *

dwarf2_evaluate_loc_desc (struct symbol *var, struct frame_info *frame,

                          gdb_byte *data, unsigned short size,

                          struct objfile *objfile)

{

  struct gdbarch *arch = get_frame_arch (frame);

  struct value *retval;

  struct dwarf_expr_baton baton;

  struct dwarf_expr_context *ctx;

  if (size == 0)

    {

      retval = allocate_value (SYMBOL_TYPE (var));

      VALUE_LVAL (retval) = not_lval;

      set_value_optimized_out (retval, 1);

      return retval;

    }

  baton.frame = frame;

  baton.objfile = objfile;

  ctx = new_dwarf_expr_context ();

  ctx->baton = &baton;

  ctx->read_reg = dwarf_expr_read_reg;

  ctx->read_mem = dwarf_expr_read_mem;

  ctx->get_frame_base = dwarf_expr_frame_base;

  ctx->get_tls_address = dwarf_expr_tls_address;

  dwarf_expr_eval (ctx, data, size);

  if (ctx->num_pieces > 0)

    {

      int i;

      long offset = 0;

      bfd_byte *contents;

      retval = allocate_value (SYMBOL_TYPE (var));

      contents = value_contents_raw (retval);

      for (i = 0; i < ctx->num_pieces; i++)

        {

          struct dwarf_expr_piece *p = &ctx->pieces[i];

          if (p->in_reg)

            {

              bfd_byte regval[MAX_REGISTER_SIZE];

              int gdb_regnum = gdbarch_dwarf2_reg_to_regnum

                                 (arch, p->value);

              get_frame_register (frame, gdb_regnum, regval);

              memcpy (contents + offset, regval, p->size);

            }

          else /* In memory?  */

            {

              read_memory (p->value, contents + offset, p->size);

            }

          offset += p->size;

        }

    }

  else if (ctx->in_reg)

    {

      CORE_ADDR dwarf_regnum = dwarf_expr_fetch (ctx, 0);

      int gdb_regnum = gdbarch_dwarf2_reg_to_regnum

                         (arch, dwarf_regnum);

      retval = value_from_register (SYMBOL_TYPE (var), gdb_regnum, frame);

    }

  else

    {

      CORE_ADDR address = dwarf_expr_fetch (ctx, 0);

      retval = allocate_value (SYMBOL_TYPE (var));

      VALUE_LVAL (retval) = lval_memory;

      set_value_lazy (retval, 1);

      VALUE_ADDRESS (retval) = address;

    }

  set_value_initialized (retval, ctx->initialized);

  free_dwarf_expr_context (ctx);

  return retval;

}

/* Helper functions and baton for dwarf2_loc_desc_needs_frame.  */

struct needs_frame_baton

{

  int needs_frame;

};

/* Reads from registers do require a frame.  */

static CORE_ADDR

needs_frame_read_reg (void *baton, int regnum)

{

  struct needs_frame_baton *nf_baton = baton;

  nf_baton->needs_frame = 1;

  return 1;

}

/* Reads from memory do not require a frame.  */

static void

needs_frame_read_mem (void *baton, gdb_byte *buf, CORE_ADDR addr, size_t len)

{

  memset (buf, 0, len);

}

/* Frame-relative accesses do require a frame.  */

static void

needs_frame_frame_base (void *baton, gdb_byte **start, size_t * length)

{

  static gdb_byte lit0 = DW_OP_lit0;

  struct needs_frame_baton *nf_baton = baton;

  *start = &lit0;

  *length = 1;

  nf_baton->needs_frame = 1;

}

/* Thread-local accesses do require a frame.  */

static CORE_ADDR

needs_frame_tls_address (void *baton, CORE_ADDR offset)

{

  struct needs_frame_baton *nf_baton = baton;

  nf_baton->needs_frame = 1;

  return 1;

}

/* Return non-zero iff the location expression at DATA (length SIZE)

   requires a frame to evaluate.  */

static int

dwarf2_loc_desc_needs_frame (gdb_byte *data, unsigned short size)

{

  struct needs_frame_baton baton;

  struct dwarf_expr_context *ctx;

  int in_reg;

  baton.needs_frame = 0;

  ctx = new_dwarf_expr_context ();

  ctx->baton = &baton;

  ctx->read_reg = needs_frame_read_reg;

  ctx->read_mem = needs_frame_read_mem;

  ctx->get_frame_base = needs_frame_frame_base;

  ctx->get_tls_address = needs_frame_tls_address;

  dwarf_expr_eval (ctx, data, size);

  in_reg = ctx->in_reg;

  if (ctx->num_pieces > 0)

    {

      int i;

      /* If the location has several pieces, and any of them are in

         registers, then we will need a frame to fetch them from.  */

      for (i = 0; i < ctx->num_pieces; i++)

        if (ctx->pieces[i].in_reg)

          in_reg = 1;

    }

  free_dwarf_expr_context (ctx);

  return baton.needs_frame || in_reg;

}

static void

dwarf2_tracepoint_var_ref (struct symbol *symbol, struct agent_expr *ax,

                           struct axs_value *value, gdb_byte *data,

                           int size)

{

  if (size == 0)

    error (_("Symbol \"%s\" has been optimized out."),

           SYMBOL_PRINT_NAME (symbol));

  if (size == 1

      && data[0] >= DW_OP_reg0

      && data[0] <= DW_OP_reg31)

    {

      value->kind = axs_lvalue_register;

      value->u.reg = data[0] - DW_OP_reg0;

    }

  else if (data[0] == DW_OP_regx)

    {

      ULONGEST reg;

      read_uleb128 (data + 1, data + size, &reg);

      value->kind = axs_lvalue_register;

      value->u.reg = reg;

    }

  else if (data[0] == DW_OP_fbreg)

    {

      /* And this is worse than just minimal; we should honor the frame base

         as above.  */

      int frame_reg;

      LONGEST frame_offset;

      gdb_byte *buf_end;

      buf_end = read_sleb128 (data + 1, data + size, &frame_offset);

      if (buf_end != data + size)

        error (_("Unexpected opcode after DW_OP_fbreg for symbol \"%s\"."),

               SYMBOL_PRINT_NAME (symbol));

      gdbarch_virtual_frame_pointer (current_gdbarch,

                                     ax->scope, &frame_reg, &frame_offset);

      ax_reg (ax, frame_reg);

      ax_const_l (ax, frame_offset);

      ax_simple (ax, aop_add);

      value->kind = axs_lvalue_memory;

    }

  else if (data[0] >= DW_OP_breg0

           && data[0] <= DW_OP_breg31)

    {

      unsigned int reg;

      LONGEST offset;

      gdb_byte *buf_end;

      reg = data[0] - DW_OP_breg0;

      buf_end = read_sleb128 (data + 1, data + size, &offset);

      if (buf_end != data + size)

        error (_("Unexpected opcode after DW_OP_breg%u for symbol \"%s\"."),

               reg, SYMBOL_PRINT_NAME (symbol));

      ax_reg (ax, reg);

      ax_const_l (ax, offset);

      ax_simple (ax, aop_add);

      value->kind = axs_lvalue_memory;

    }

  else

    error (_("Unsupported DWARF opcode 0x%x in the location of \"%s\"."),

           data[0], SYMBOL_PRINT_NAME (symbol));

}

/* Return the value of SYMBOL in FRAME using the DWARF-2 expression

   evaluator to calculate the location.  */

static struct value *

locexpr_read_variable (struct symbol *symbol, struct frame_info *frame)

{

  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);

  struct value *val;

  val = dwarf2_evaluate_loc_desc (symbol, frame, dlbaton->data, dlbaton->size,

                                  dlbaton->objfile);

  return val;

}

/* Return non-zero iff we need a frame to evaluate SYMBOL.  */

static int

locexpr_read_needs_frame (struct symbol *symbol)

{

  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);

  return dwarf2_loc_desc_needs_frame (dlbaton->data, dlbaton->size);

}

/* Print a natural-language description of SYMBOL to STREAM.  */

static int

locexpr_describe_location (struct symbol *symbol, struct ui_file *stream)

{

  /* FIXME: be more extensive.  */

  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);

  if (dlbaton->size == 1

      && dlbaton->data[0] >= DW_OP_reg0

      && dlbaton->data[0] <= DW_OP_reg31)

    {

      int regno = gdbarch_dwarf2_reg_to_regnum

                    (current_gdbarch, dlbaton->data[0] - DW_OP_reg0);

      fprintf_filtered (stream,

                        "a variable in register %s",

                        gdbarch_register_name (current_gdbarch, regno));

      return 1;

    }

  /* The location expression for a TLS variable looks like this (on a

     64-bit LE machine):

     DW_AT_location    : 10 byte block: 3 4 0 0 0 0 0 0 0 e0

                        (DW_OP_addr: 4; DW_OP_GNU_push_tls_address)

     0x3 is the encoding for DW_OP_addr, which has an operand as long

     as the size of an address on the target machine (here is 8

     bytes).  0xe0 is the encoding for DW_OP_GNU_push_tls_address.

     The operand represents the offset at which the variable is within

     the thread local storage.  */

  if (dlbaton->size > 1

      && dlbaton->data[dlbaton->size - 1] == DW_OP_GNU_push_tls_address)

    if (dlbaton->data[0] == DW_OP_addr)

      {

        int bytes_read;

        CORE_ADDR offset = dwarf2_read_address (&dlbaton->data[1],

                                                &dlbaton->data[dlbaton->size - 1],

                                                &bytes_read);

        fprintf_filtered (stream,

                          "a thread-local variable at offset %s in the "

                          "thread-local storage for `%s'",

                          paddr_nz (offset), dlbaton->objfile->name);

        return 1;

      }

  fprintf_filtered (stream,

                    "a variable with complex or multiple locations (DWARF2)");

  return 1;

}

/* Describe the location of SYMBOL as an agent value in VALUE, generating

   any necessary bytecode in AX.

   NOTE drow/2003-02-26: This function is extremely minimal, because

   doing it correctly is extremely complicated and there is no

   publicly available stub with tracepoint support for me to test

   against.  When there is one this function should be revisited.  */

static void

locexpr_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,

                            struct axs_value * value)

{

  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);

  dwarf2_tracepoint_var_ref (symbol, ax, value, dlbaton->data, dlbaton->size);

}

/* The set of location functions used with the DWARF-2 expression

   evaluator.  */

const struct symbol_ops dwarf2_locexpr_funcs = {

  locexpr_read_variable,

  locexpr_read_needs_frame,

  locexpr_describe_location,

  locexpr_tracepoint_var_ref

};

/* Wrapper functions for location lists.  These generally find

   the appropriate location expression and call something above.  */

/* Return the value of SYMBOL in FRAME using the DWARF-2 expression

   evaluator to calculate the location.  */

static struct value *

loclist_read_variable (struct symbol *symbol, struct frame_info *frame)

{

  struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);

  struct value *val;

  gdb_byte *data;

  size_t size;

  data = find_location_expression (dlbaton, &size,

                                   frame ? get_frame_address_in_block (frame)

                                   : 0);

  if (data == NULL)

    {

      val = allocate_value (SYMBOL_TYPE (symbol));

      VALUE_LVAL (val) = not_lval;

      set_value_optimized_out (val, 1);

    }

  else

    val = dwarf2_evaluate_loc_desc (symbol, frame, data, size,

                                    dlbaton->objfile);

  return val;

}

/* Return non-zero iff we need a frame to evaluate SYMBOL.  */

static int

loclist_read_needs_frame (struct symbol *symbol)

{

  /* If there's a location list, then assume we need to have a frame

     to choose the appropriate location expression.  With tracking of

     global variables this is not necessarily true, but such tracking

     is disabled in GCC at the moment until we figure out how to

     represent it.  */

  return 1;

}

/* Print a natural-language description of SYMBOL to STREAM.  */

static int

loclist_describe_location (struct symbol *symbol, struct ui_file *stream)

{

  /* FIXME: Could print the entire list of locations.  */

  fprintf_filtered (stream, "a variable with multiple locations");

  return 1;

}

/* Describe the location of SYMBOL as an agent value in VALUE, generating

   any necessary bytecode in AX.  */

static void

loclist_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,

                            struct axs_value * value)

{

  struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);

  gdb_byte *data;

  size_t size;

  data = find_location_expression (dlbaton, &size, ax->scope);

  if (data == NULL)

    error (_("Variable \"%s\" is not available."), SYMBOL_NATURAL_NAME (symbol));

  dwarf2_tracepoint_var_ref (symbol, ax, value, data, size);

}

/* The set of location functions used with the DWARF-2 expression

   evaluator and location lists.  */

const struct symbol_ops dwarf2_loclist_funcs = {

  loclist_read_variable,

  loclist_read_needs_frame,

  loclist_describe_location,

  loclist_tracepoint_var_ref

};