path: root/gdb/dwarf2expr.c

/* Dwarf2 Expression Evaluator
   Copyright 2001, 2002, 2003 Free Software Foundation, Inc.
   Contributed by Daniel Berlin (dan@dberlin.org)

   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 2 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, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include "defs.h"
#include "symtab.h"
#include "gdbtypes.h"
#include "value.h"
#include "gdbcore.h"
#include "elf/dwarf2.h"
#include "dwarf2expr.h"

/* Local prototypes.  */

static void execute_stack_op (struct dwarf_expr_context *,
			      unsigned char *, unsigned char *);

/* Create a new context for the expression evaluator.  */

struct dwarf_expr_context *
new_dwarf_expr_context (void)
{
  struct dwarf_expr_context *retval;
  retval = xcalloc (1, sizeof (struct dwarf_expr_context));
  retval->stack_len = 10;
  retval->stack = xmalloc (10 * sizeof (CORE_ADDR));
  return retval;
}

/* Release the memory allocated to CTX.  */

void
free_dwarf_expr_context (struct dwarf_expr_context *ctx)
{
  xfree (ctx->stack);
  xfree (ctx);
}

/* Expand the memory allocated to CTX's stack to contain at least
   NEED more elements than are currently used.  */

static void
dwarf_expr_grow_stack (struct dwarf_expr_context *ctx, size_t need)
{
  if (ctx->stack_len + need > ctx->stack_allocated)
    {
      size_t templen = ctx->stack_len * 2;
      while (templen < (ctx->stack_len + need))
	   templen *= 2;
      ctx->stack = xrealloc (ctx->stack,
			     templen * sizeof (CORE_ADDR));
      ctx->stack_allocated = templen;
    }
}

/* Push VALUE onto CTX's stack.  */

void
dwarf_expr_push (struct dwarf_expr_context *ctx, CORE_ADDR value)
{
  dwarf_expr_grow_stack (ctx, 1);
  ctx->stack[ctx->stack_len++] = value;
}

/* Pop the top item off of CTX's stack.  */

void
dwarf_expr_pop (struct dwarf_expr_context *ctx)
{
  if (ctx->stack_len <= 0)
    error ("dwarf expression stack underflow");
  ctx->stack_len--;
}

/* Retrieve the N'th item on CTX's stack.  */

CORE_ADDR
dwarf_expr_fetch (struct dwarf_expr_context *ctx, int n)
{
  if (ctx->stack_len < n)
     error ("Asked for position %d of stack, stack only has %d elements on it\n",
	    n, ctx->stack_len);
  return ctx->stack[ctx->stack_len - (1 + n)];

}

/* Evaluate the expression at ADDR (LEN bytes long) using the context
   CTX.  */

void
dwarf_expr_eval (struct dwarf_expr_context *ctx, unsigned char *addr,
		 size_t len)
{
  execute_stack_op (ctx, addr, addr + len);
}

/* Decode the unsigned LEB128 constant at BUF into the variable pointed to
   by R, and return the new value of BUF.  Verify that it doesn't extend
   past BUF_END.  */

unsigned char *
read_uleb128 (unsigned char *buf, unsigned char *buf_end, ULONGEST * r)
{
  unsigned shift = 0;
  ULONGEST result = 0;
  unsigned char byte;

  while (1)
    {
      if (buf >= buf_end)
	error ("read_uleb128: Corrupted DWARF expression.");

      byte = *buf++;
      result |= (byte & 0x7f) << shift;
      if ((byte & 0x80) == 0)
	break;
      shift += 7;
    }
  *r = result;
  return buf;
}

/* Decode the signed LEB128 constant at BUF into the variable pointed to
   by R, and return the new value of BUF.  Verify that it doesn't extend
   past BUF_END.  */

unsigned char *
read_sleb128 (unsigned char *buf, unsigned char *buf_end, LONGEST * r)
{
  unsigned shift = 0;
  LONGEST result = 0;
  unsigned char byte;

  while (1)
    {
      if (buf >= buf_end)
	error ("read_sleb128: Corrupted DWARF expression.");

      byte = *buf++;
      result |= (byte & 0x7f) << shift;
      shift += 7;
      if ((byte & 0x80) == 0)
	break;
    }
  if (shift < (sizeof (*r) * 8) && (byte & 0x40) != 0)
    result |= -(1 << shift);

  *r = result;
  return buf;
}

/* Read an address from BUF, and verify that it doesn't extend past
   BUF_END.  The address is returned, and *BYTES_READ is set to the
   number of bytes read from BUF.  */

CORE_ADDR
dwarf2_read_address (unsigned char *buf, unsigned char *buf_end, int *bytes_read)
{
  CORE_ADDR result;

  if (buf_end - buf < TARGET_ADDR_BIT / TARGET_CHAR_BIT)
    error ("dwarf2_read_address: Corrupted DWARF expression.");

  *bytes_read = TARGET_ADDR_BIT / TARGET_CHAR_BIT;
  result = extract_address (buf, TARGET_ADDR_BIT / TARGET_CHAR_BIT);
  return result;
}

/* Return the type of an address, for unsigned arithmetic.  */

static struct type *
unsigned_address_type (void)
{
  switch (TARGET_ADDR_BIT / TARGET_CHAR_BIT)
    {
    case 2:
      return builtin_type_uint16;
    case 4:
      return builtin_type_uint32;
    case 8:
      return builtin_type_uint64;
    default:
      internal_error (__FILE__, __LINE__,
		      "Unsupported address size.\n");
    }
}

/* Return the type of an address, for signed arithmetic.  */

static struct type *
signed_address_type (void)
{
  switch (TARGET_ADDR_BIT / TARGET_CHAR_BIT)
    {
    case 2:
      return builtin_type_int16;
    case 4:
      return builtin_type_int32;
    case 8:
      return builtin_type_int64;
    default:
      internal_error (__FILE__, __LINE__,
		      "Unsupported address size.\n");
    }
}

/* The engine for the expression evaluator.  Using the context in CTX,
   evaluate the expression between OP_PTR and OP_END.  */

static void
execute_stack_op (struct dwarf_expr_context *ctx, unsigned char *op_ptr,
		  unsigned char *op_end)
{
  while (op_ptr < op_end)
    {
      enum dwarf_location_atom op = *op_ptr++;
      CORE_ADDR result, memaddr;
      ULONGEST uoffset, reg;
      LONGEST offset;
      int bytes_read;
      enum lval_type expr_lval;

      ctx->in_reg = 0;

      switch (op)
	{
	case DW_OP_lit0:
	case DW_OP_lit1:
	case DW_OP_lit2:
	case DW_OP_lit3:
	case DW_OP_lit4:
	case DW_OP_lit5:
	case DW_OP_lit6:
	case DW_OP_lit7:
	case DW_OP_lit8:
	case DW_OP_lit9:
	case DW_OP_lit10:
	case DW_OP_lit11:
	case DW_OP_lit12:
	case DW_OP_lit13:
	case DW_OP_lit14:
	case DW_OP_lit15:
	case DW_OP_lit16:
	case DW_OP_lit17:
	case DW_OP_lit18:
	case DW_OP_lit19:
	case DW_OP_lit20:
	case DW_OP_lit21:
	case DW_OP_lit22:
	case DW_OP_lit23:
	case DW_OP_lit24:
	case DW_OP_lit25:
	case DW_OP_lit26:
	case DW_OP_lit27:
	case DW_OP_lit28:
	case DW_OP_lit29:
	case DW_OP_lit30:
	case DW_OP_lit31:
	  result = op - DW_OP_lit0;
	  break;

	case DW_OP_addr:
	  result = dwarf2_read_address (op_ptr, op_end, &bytes_read);
	  op_ptr += bytes_read;
	  break;

	case DW_OP_const1u:
	  result = extract_unsigned_integer (op_ptr, 1);
	  op_ptr += 1;
	  break;
	case DW_OP_const1s:
	  result = extract_signed_integer (op_ptr, 1);
	  op_ptr += 1;
	  break;
	case DW_OP_const2u:
	  result = extract_unsigned_integer (op_ptr, 2);
	  op_ptr += 2;
	  break;
	case DW_OP_const2s:
	  result = extract_signed_integer (op_ptr, 2);
	  op_ptr += 2;
	  break;
	case DW_OP_const4u:
	  result = extract_unsigned_integer (op_ptr, 4);
	  op_ptr += 4;
	  break;
	case DW_OP_const4s:
	  result = extract_signed_integer (op_ptr, 4);
	  op_ptr += 4;
	  break;
	case DW_OP_const8u:
	  result = extract_unsigned_integer (op_ptr, 8);
	  op_ptr += 8;
	  break;
	case DW_OP_const8s:
	  result = extract_signed_integer (op_ptr, 8);
	  op_ptr += 8;
	  break;
	case DW_OP_constu:
	  op_ptr = read_uleb128 (op_ptr, op_end, &uoffset);
	  result = uoffset;
	  break;
	case DW_OP_consts:
	  op_ptr = read_sleb128 (op_ptr, op_end, &offset);
	  result = offset;
	  break;

	/* The DW_OP_reg operations are required to occur alone in
	   location expressions.  */
	case DW_OP_reg0:
	case DW_OP_reg1:
	case DW_OP_reg2:
	case DW_OP_reg3:
	case DW_OP_reg4:
	case DW_OP_reg5:
	case DW_OP_reg6:
	case DW_OP_reg7:
	case DW_OP_reg8:
	case DW_OP_reg9:
	case DW_OP_reg10:
	case DW_OP_reg11:
	case DW_OP_reg12:
	case DW_OP_reg13:
	case DW_OP_reg14:
	case DW_OP_reg15:
	case DW_OP_reg16:
	case DW_OP_reg17:
	case DW_OP_reg18:
	case DW_OP_reg19:
	case DW_OP_reg20:
	case DW_OP_reg21:
	case DW_OP_reg22:
	case DW_OP_reg23:
	case DW_OP_reg24:
	case DW_OP_reg25:
	case DW_OP_reg26:
	case DW_OP_reg27:
	case DW_OP_reg28:
	case DW_OP_reg29:
	case DW_OP_reg30:
	case DW_OP_reg31:
	  /* NOTE: in the presence of DW_OP_piece this check is incorrect.  */
	  if (op_ptr != op_end)
	    error ("DWARF-2 expression error: DW_OP_reg operations must be "
		   "used alone.");

	  /* FIXME drow/2003-02-21: This call to read_reg could be pushed
	     into the evaluator's caller by changing the semantics for in_reg.
	     Then we wouldn't need to return an lval_type and a memaddr.  */
	  result = (ctx->read_reg) (ctx->baton, op - DW_OP_reg0, &expr_lval,
				    &memaddr);

	  if (expr_lval == lval_register)
	    {
	      ctx->regnum = op - DW_OP_reg0;
	      ctx->in_reg = 1;
	    }
	  else
	    result = memaddr;

	  break;

	case DW_OP_regx:
	  op_ptr = read_uleb128 (op_ptr, op_end, &reg);
	  if (op_ptr != op_end)
	    error ("DWARF-2 expression error: DW_OP_reg operations must be "
		   "used alone.");

	  result = (ctx->read_reg) (ctx->baton, reg, &expr_lval, &memaddr);

	  if (expr_lval == lval_register)
	    {
	      ctx->regnum = reg;
	      ctx->in_reg = 1;
	    }
	  else
	    result = memaddr;

	  break;

	case DW_OP_breg0:
	case DW_OP_breg1:
	case DW_OP_breg2:
	case DW_OP_breg3:
	case DW_OP_breg4:
	case DW_OP_breg5:
	case DW_OP_breg6:
	case DW_OP_breg7:
	case DW_OP_breg8:
	case DW_OP_breg9:
	case DW_OP_breg10:
	case DW_OP_breg11:
	case DW_OP_breg12:
	case DW_OP_breg13:
	case DW_OP_breg14:
	case DW_OP_breg15:
	case DW_OP_breg16:
	case DW_OP_breg17:
	case DW_OP_breg18:
	case DW_OP_breg19:
	case DW_OP_breg20:
	case DW_OP_breg21:
	case DW_OP_breg22:
	case DW_OP_breg23:
	case DW_OP_breg24:
	case DW_OP_breg25:
	case DW_OP_breg26:
	case DW_OP_breg27:
	case DW_OP_breg28:
	case DW_OP_breg29:
	case DW_OP_breg30:
	case DW_OP_breg31:
	  {
	    op_ptr = read_sleb128 (op_ptr, op_end, &offset);
	    result = (ctx->read_reg) (ctx->baton, op - DW_OP_breg0,
				      &expr_lval, &memaddr);
	    result += offset;
	  }
	  break;
	case DW_OP_bregx:
	  {
	    op_ptr = read_uleb128 (op_ptr, op_end, &reg);
	    op_ptr = read_sleb128 (op_ptr, op_end, &offset);
	    result = (ctx->read_reg) (ctx->baton, reg, &expr_lval, &memaddr);
	    result += offset;
	  }
	  break;
	case DW_OP_fbreg:
	  {
	    unsigned char *datastart;
	    size_t datalen;
	    unsigned int before_stack_len;

	    op_ptr = read_sleb128 (op_ptr, op_end, &offset);
	    /* Rather than create a whole new context, we simply
	       record the stack length before execution, then reset it
	       afterwards, effectively erasing whatever the recursive
	       call put there.  */
	    before_stack_len = ctx->stack_len;
	    /* FIXME: cagney/2003-03-26: This code should be using
               get_frame_base_address(), and then implement a dwarf2
               specific this_base method.  */
	    (ctx->get_frame_base) (ctx->baton, &datastart, &datalen);
	    dwarf_expr_eval (ctx, datastart, datalen);
	    result = dwarf_expr_fetch (ctx, 0);
	    if (! ctx->in_reg)
	      {
		char *buf = alloca (TARGET_ADDR_BIT / TARGET_CHAR_BIT);
		int bytes_read;

		(ctx->read_mem) (ctx->baton, buf, result,
				 TARGET_ADDR_BIT / TARGET_CHAR_BIT);
		result = dwarf2_read_address (buf,
					      buf + (TARGET_ADDR_BIT
						     / TARGET_CHAR_BIT),
					      &bytes_read);
	      }
	    result = result + offset;
	    ctx->stack_len = before_stack_len;
	    ctx->in_reg = 0;
	  }
	  break;
	case DW_OP_dup:
	  result = dwarf_expr_fetch (ctx, 0);
	  break;

	case DW_OP_drop:
	  dwarf_expr_pop (ctx);
	  goto no_push;

	case DW_OP_pick:
	  offset = *op_ptr++;
	  result = dwarf_expr_fetch (ctx, offset);
	  break;

	case DW_OP_over:
	  result = dwarf_expr_fetch (ctx, 1);
	  break;

	case DW_OP_rot:
	  {
	    CORE_ADDR t1, t2, t3;

	    if (ctx->stack_len < 3)
	       error ("Not enough elements for DW_OP_rot. Need 3, have %d\n",
		      ctx->stack_len);
	    t1 = ctx->stack[ctx->stack_len - 1];
	    t2 = ctx->stack[ctx->stack_len - 2];
	    t3 = ctx->stack[ctx->stack_len - 3];
	    ctx->stack[ctx->stack_len - 1] = t2;
	    ctx->stack[ctx->stack_len - 2] = t3;
	    ctx->stack[ctx->stack_len - 3] = t1;
	    goto no_push;
	  }

	case DW_OP_deref:
	case DW_OP_deref_size:
	case DW_OP_abs:
	case DW_OP_neg:
	case DW_OP_not:
	case DW_OP_plus_uconst:
	  /* Unary operations.  */
	  result = dwarf_expr_fetch (ctx, 0);
	  dwarf_expr_pop (ctx);

	  switch (op)
	    {
	    case DW_OP_deref:
	      {
		char *buf = alloca (TARGET_ADDR_BIT / TARGET_CHAR_BIT);
		int bytes_read;

		(ctx->read_mem) (ctx->baton, buf, result,
				 TARGET_ADDR_BIT / TARGET_CHAR_BIT);
		result = dwarf2_read_address (buf,
					      buf + (TARGET_ADDR_BIT
						     / TARGET_CHAR_BIT),
					      &bytes_read);
	      }
	      break;

	    case DW_OP_deref_size:
	      {
		char *buf = alloca (TARGET_ADDR_BIT / TARGET_CHAR_BIT);
		int bytes_read;

		(ctx->read_mem) (ctx->baton, buf, result, *op_ptr++);
		result = dwarf2_read_address (buf,
					      buf + (TARGET_ADDR_BIT
						     / TARGET_CHAR_BIT),
					      &bytes_read);
	      }
	      break;

	    case DW_OP_abs:
	      if ((signed int) result < 0)
		result = -result;
	      break;
	    case DW_OP_neg:
	      result = -result;
	      break;
	    case DW_OP_not:
	      result = ~result;
	      break;
	    case DW_OP_plus_uconst:
	      op_ptr = read_uleb128 (op_ptr, op_end, &reg);
	      result += reg;
	      break;
	    }
	  break;

	case DW_OP_and:
	case DW_OP_div:
	case DW_OP_minus:
	case DW_OP_mod:
	case DW_OP_mul:
	case DW_OP_or:
	case DW_OP_plus:
	case DW_OP_shl:
	case DW_OP_shr:
	case DW_OP_shra:
	case DW_OP_xor:
	case DW_OP_le:
	case DW_OP_ge:
	case DW_OP_eq:
	case DW_OP_lt:
	case DW_OP_gt:
	case DW_OP_ne:
	  {
	    /* Binary operations.  Use the value engine to do computations in
	       the right width.  */
	    CORE_ADDR first, second;
	    enum exp_opcode binop;
	    struct value *val1, *val2;

	    second = dwarf_expr_fetch (ctx, 0);
	    dwarf_expr_pop (ctx);

	    first = dwarf_expr_fetch (ctx, 1);
	    dwarf_expr_pop (ctx);

	    val1 = value_from_longest (unsigned_address_type (), first);
	    val2 = value_from_longest (unsigned_address_type (), second);

	    switch (op)
	      {
	      case DW_OP_and:
		binop = BINOP_BITWISE_AND;
		break;
	      case DW_OP_div:
		binop = BINOP_DIV;
	      case DW_OP_minus:
		binop = BINOP_SUB;
		break;
	      case DW_OP_mod:
		binop = BINOP_MOD;
		break;
	      case DW_OP_mul:
		binop = BINOP_MUL;
		break;
	      case DW_OP_or:
		binop = BINOP_BITWISE_IOR;
		break;
	      case DW_OP_plus:
		binop = BINOP_ADD;
		break;
	      case DW_OP_shl:
		binop = BINOP_LSH;
		break;
	      case DW_OP_shr:
		binop = BINOP_RSH;
	      case DW_OP_shra:
		binop = BINOP_RSH;
		val1 = value_from_longest (signed_address_type (), first);
		break;
	      case DW_OP_xor:
		binop = BINOP_BITWISE_XOR;
		break;
	      case DW_OP_le:
		binop = BINOP_LEQ;
		break;
	      case DW_OP_ge:
		binop = BINOP_GEQ;
		break;
	      case DW_OP_eq:
		binop = BINOP_EQUAL;
		break;
	      case DW_OP_lt:
		binop = BINOP_LESS;
		break;
	      case DW_OP_gt:
		binop = BINOP_GTR;
		break;
	      case DW_OP_ne:
		binop = BINOP_NOTEQUAL;
		break;
	      default:
		internal_error (__FILE__, __LINE__,
				"Can't be reached.");
	      }
	    result = value_as_long (value_binop (val1, val2, binop));
	  }
	  break;

	case DW_OP_GNU_push_tls_address:
	  result = dwarf_expr_fetch (ctx, 0);
	  dwarf_expr_pop (ctx);
	  result = (ctx->get_tls_address) (ctx->baton, result);
	  break;

	case DW_OP_skip:
	  offset = extract_signed_integer (op_ptr, 2);
	  op_ptr += 2;
	  op_ptr += offset;
	  goto no_push;

	case DW_OP_bra:
	  offset = extract_signed_integer (op_ptr, 2);
	  op_ptr += 2;
	  if (dwarf_expr_fetch (ctx, 0) != 0)
	    op_ptr += offset;
	  dwarf_expr_pop (ctx);
	  goto no_push;

	case DW_OP_nop:
	  goto no_push;

	default:
	  error ("Unhandled dwarf expression opcode");
	}

      /* Most things push a result value.  */
      dwarf_expr_push (ctx, result);
    no_push:;
    }
}