gdb/dwarf2/expr.h

   1 /* DWARF 2 Expression Evaluator.
   2
   3    Copyright (C) 2001-2022 Free Software Foundation, Inc.
   4
   5    Contributed by Daniel Berlin <dan@dberlin.org>.
   6
   7    This file is part of GDB.
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  21
  22 #if !defined (DWARF2EXPR_H)
  23 #define DWARF2EXPR_H
  24
  25 #include "leb128.h"
  26 #include "gdbtypes.h"
  27
  28 struct dwarf2_per_objfile;
  29
  30 /* The location of a value.  */
  31 enum dwarf_value_location
  32 {
  33   /* The piece is in memory.
  34      The value on the dwarf stack is its address.  */
  35   DWARF_VALUE_MEMORY,
  36
  37   /* The piece is in a register.
  38      The value on the dwarf stack is the register number.  */
  39   DWARF_VALUE_REGISTER,
  40
  41   /* The piece is on the dwarf stack.  */
  42   DWARF_VALUE_STACK,
  43
  44   /* The piece is a literal.  */
  45   DWARF_VALUE_LITERAL,
  46
  47   /* The piece was optimized out.  */
  48   DWARF_VALUE_OPTIMIZED_OUT,
  49
  50   /* The piece is an implicit pointer.  */
  51   DWARF_VALUE_IMPLICIT_POINTER
  52 };
  53
  54 /* A piece of an object, as recorded by DW_OP_piece or DW_OP_bit_piece.  */
  55 struct dwarf_expr_piece
  56 {
  57   enum dwarf_value_location location;
  58
  59   union
  60   {
  61     struct
  62     {
  63       /* This piece's address, for DWARF_VALUE_MEMORY pieces.  */
  64       CORE_ADDR addr;
  65       /* Non-zero if the piece is known to be in memory and on
  66          the program's stack.  */
  67       bool in_stack_memory;
  68     } mem;
  69
  70     /* The piece's register number, for DWARF_VALUE_REGISTER pieces.  */
  71     int regno;
  72
  73     /* The piece's literal value, for DWARF_VALUE_STACK pieces.  */
  74     struct value *value;
  75
  76     struct
  77     {
  78       /* A pointer to the data making up this piece,
  79          for DWARF_VALUE_LITERAL pieces.  */
  80       const gdb_byte *data;
  81       /* The length of the available data.  */
  82       ULONGEST length;
  83     } literal;
  84
  85     /* Used for DWARF_VALUE_IMPLICIT_POINTER.  */
  86     struct
  87     {
  88       /* The referent DIE from DW_OP_implicit_pointer.  */
  89       sect_offset die_sect_off;
  90       /* The byte offset into the resulting data.  */
  91       LONGEST offset;
  92     } ptr;
  93   } v;
  94
  95   /* The length of the piece, in bits.  */
  96   ULONGEST size;
  97   /* The piece offset, in bits.  */
  98   ULONGEST offset;
  99 };
 100
 101 /* The dwarf expression stack.  */
 102
 103 struct dwarf_stack_value
 104 {
 105   dwarf_stack_value (struct value *value_, int in_stack_memory_)
 106   : value (value_), in_stack_memory (in_stack_memory_)
 107   {}
 108
 109   struct value *value;
 110
 111   /* True if the piece is in memory and is known to be on the program's stack.
 112      It is always ok to set this to zero.  This is used, for example, to
 113      optimize memory access from the target.  It can vastly speed up backtraces
 114      on long latency connections when "set stack-cache on".  */
 115   bool in_stack_memory;
 116 };
 117
 118 /* The expression evaluator works with a dwarf_expr_context, describing
 119    its current state and its callbacks.  */
 120 struct dwarf_expr_context
 121 {
 122   dwarf_expr_context (dwarf2_per_objfile *per_objfile,
 123                       int addr_size);
 124   virtual ~dwarf_expr_context () = default;
 125
 126   void push_address (CORE_ADDR value, bool in_stack_memory);
 127
 128   /* Evaluate the expression at ADDR (LEN bytes long) in a given PER_CU
 129      and FRAME context.
 130
 131      AS_LVAL defines if the returned struct value is expected to be a
 132      value (false) or a location description (true).
 133
 134      TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET describe the expected struct
 135      value representation of the evaluation result.
 136
 137      The ADDR_INFO property can be specified to override the range of
 138      memory addresses with the passed in buffer.  */
 139   value *evaluate (const gdb_byte *addr, size_t len, bool as_lval,
 140                    dwarf2_per_cu_data *per_cu, frame_info *frame,
 141                    const struct property_addr_info *addr_info = nullptr,
 142                    struct type *type = nullptr,
 143                    struct type *subobj_type = nullptr,
 144                    LONGEST subobj_offset = 0);
 145
 146 private:
 147   /* The stack of values.  */
 148   std::vector<dwarf_stack_value> m_stack;
 149
 150   /* Target address size in bytes.  */
 151   int m_addr_size = 0;
 152
 153   /* The current depth of dwarf expression recursion, via DW_OP_call*,
 154      DW_OP_fbreg, DW_OP_push_object_address, etc., and the maximum
 155      depth we'll tolerate before raising an error.  */
 156   int m_recursion_depth = 0, m_max_recursion_depth = 0x100;
 157
 158   /* Location of the value.  */
 159   dwarf_value_location m_location = DWARF_VALUE_MEMORY;
 160
 161   /* For DWARF_VALUE_LITERAL, the current literal value's length and
 162      data.  For DWARF_VALUE_IMPLICIT_POINTER, LEN is the offset of the
 163      target DIE of sect_offset kind.  */
 164   ULONGEST m_len = 0;
 165   const gdb_byte *m_data = nullptr;
 166
 167   /* Initialization status of variable: Non-zero if variable has been
 168      initialized; zero otherwise.  */
 169   int m_initialized = 0;
 170
 171   /* A vector of pieces.
 172
 173      Each time DW_OP_piece is executed, we add a new element to the
 174      end of this array, recording the current top of the stack, the
 175      current location, and the size given as the operand to
 176      DW_OP_piece.  We then pop the top value from the stack, reset the
 177      location, and resume evaluation.
 178
 179      The Dwarf spec doesn't say whether DW_OP_piece pops the top value
 180      from the stack.  We do, ensuring that clients of this interface
 181      expecting to see a value left on the top of the stack (say, code
 182      evaluating frame base expressions or CFA's specified with
 183      DW_CFA_def_cfa_expression) will get an error if the expression
 184      actually marks all the values it computes as pieces.
 185
 186      If an expression never uses DW_OP_piece, num_pieces will be zero.
 187      (It would be nice to present these cases as expressions yielding
 188      a single piece, so that callers need not distinguish between the
 189      no-DW_OP_piece and one-DW_OP_piece cases.  But expressions with
 190      no DW_OP_piece operations have no value to place in a piece's
 191      'size' field; the size comes from the surrounding data.  So the
 192      two cases need to be handled separately.)  */
 193   std::vector<dwarf_expr_piece> m_pieces;
 194
 195   /* We evaluate the expression in the context of this objfile.  */
 196   dwarf2_per_objfile *m_per_objfile;
 197
 198   /* Frame information used for the evaluation.  */
 199   frame_info *m_frame = nullptr;
 200
 201   /* Compilation unit used for the evaluation.  */
 202   dwarf2_per_cu_data *m_per_cu = nullptr;
 203
 204   /* Property address info used for the evaluation.  */
 205   const struct property_addr_info *m_addr_info = nullptr;
 206
 207   void eval (const gdb_byte *addr, size_t len);
 208   struct type *address_type () const;
 209   void push (struct value *value, bool in_stack_memory);
 210   bool stack_empty_p () const;
 211   void add_piece (ULONGEST size, ULONGEST offset);
 212   void execute_stack_op (const gdb_byte *op_ptr, const gdb_byte *op_end);
 213   void pop ();
 214   struct value *fetch (int n);
 215   CORE_ADDR fetch_address (int n);
 216   bool fetch_in_stack_memory (int n);
 217
 218   /* Fetch the result of the expression evaluation in a form of
 219      a struct value, where TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET
 220      describe the source level representation of that result.
 221      AS_LVAL defines if the fetched struct value is expected to
 222      be a value or a location description.  */
 223   value *fetch_result (struct type *type, struct type *subobj_type,
 224                        LONGEST subobj_offset, bool as_lval);
 225
 226   /* Return the location expression for the frame base attribute, in
 227      START and LENGTH.  The result must be live until the current
 228      expression evaluation is complete.  */
 229   void get_frame_base (const gdb_byte **start, size_t *length);
 230
 231   /* Return the base type given by the indicated DIE at DIE_CU_OFF.
 232      This can throw an exception if the DIE is invalid or does not
 233      represent a base type.  */
 234   struct type *get_base_type (cu_offset die_cu_off);
 235
 236   /* Execute DW_AT_location expression for the DWARF expression
 237      subroutine in the DIE at DIE_CU_OFF in the CU.  Do not touch
 238      STACK while it being passed to and returned from the called DWARF
 239      subroutine.  */
 240   void dwarf_call (cu_offset die_cu_off);
 241
 242   /* Push on DWARF stack an entry evaluated for DW_TAG_call_site's
 243      parameter matching KIND and KIND_U at the caller of specified BATON.
 244      If DEREF_SIZE is not -1 then use DW_AT_call_data_value instead of
 245      DW_AT_call_value.  */
 246   void push_dwarf_reg_entry_value (call_site_parameter_kind kind,
 247                                    call_site_parameter_u kind_u,
 248                                    int deref_size);
 249
 250   /* Read LENGTH bytes at ADDR into BUF.  This method also handles the
 251      case where a caller of the evaluator passes in some data,
 252      but with the address being 0.  In this situation, we arrange for
 253      memory reads to come from the passed-in buffer.  */
 254   void read_mem (gdb_byte *buf, CORE_ADDR addr, size_t length);
 255 };
 256
 257 /* Return the value of register number REG (a DWARF register number),
 258    read as an address in a given FRAME.  */
 259 CORE_ADDR read_addr_from_reg (frame_info *frame, int reg);
 260
 261 void dwarf_expr_require_composition (const gdb_byte *, const gdb_byte *,
 262                                      const char *);
 263
 264 int dwarf_block_to_dwarf_reg (const gdb_byte *buf, const gdb_byte *buf_end);
 265
 266 int dwarf_block_to_dwarf_reg_deref (const gdb_byte *buf,
 267                                     const gdb_byte *buf_end,
 268                                     CORE_ADDR *deref_size_return);
 269
 270 int dwarf_block_to_fb_offset (const gdb_byte *buf, const gdb_byte *buf_end,
 271                               CORE_ADDR *fb_offset_return);
 272
 273 int dwarf_block_to_sp_offset (struct gdbarch *gdbarch, const gdb_byte *buf,
 274                               const gdb_byte *buf_end,
 275                               CORE_ADDR *sp_offset_return);
 276
 277 /* Wrappers around the leb128 reader routines to simplify them for our
 278    purposes.  */
 279
 280 static inline const gdb_byte *
 281 gdb_read_uleb128 (const gdb_byte *buf, const gdb_byte *buf_end,
 282                   uint64_t *r)
 283 {
 284   size_t bytes_read = read_uleb128_to_uint64 (buf, buf_end, r);
 285
 286   if (bytes_read == 0)
 287     return NULL;
 288   return buf + bytes_read;
 289 }
 290
 291 static inline const gdb_byte *
 292 gdb_read_sleb128 (const gdb_byte *buf, const gdb_byte *buf_end,
 293                   int64_t *r)
 294 {
 295   size_t bytes_read = read_sleb128_to_int64 (buf, buf_end, r);
 296
 297   if (bytes_read == 0)
 298     return NULL;
 299   return buf + bytes_read;
 300 }
 301
 302 static inline const gdb_byte *
 303 gdb_skip_leb128 (const gdb_byte *buf, const gdb_byte *buf_end)
 304 {
 305   size_t bytes_read = skip_leb128 (buf, buf_end);
 306
 307   if (bytes_read == 0)
 308     return NULL;
 309   return buf + bytes_read;
 310 }
 311
 312 extern const gdb_byte *safe_read_uleb128 (const gdb_byte *buf,
 313                                           const gdb_byte *buf_end,
 314                                           uint64_t *r);
 315
 316 extern const gdb_byte *safe_read_sleb128 (const gdb_byte *buf,
 317                                           const gdb_byte *buf_end,
 318                                           int64_t *r);
 319
 320 extern const gdb_byte *safe_skip_leb128 (const gdb_byte *buf,
 321                                          const gdb_byte *buf_end);
 322
 323 #endif /* DWARF2EXPR_H */