gdb/f-array-walker.h

   1 /* Copyright (C) 2020-2022 Free Software Foundation, Inc.
   2
   3    This file is part of GDB.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 /* Support classes to wrap up the process of iterating over a
  19    multi-dimensional Fortran array.  */
  20
  21 #ifndef F_ARRAY_WALKER_H
  22 #define F_ARRAY_WALKER_H
  23
  24 #include "defs.h"
  25 #include "gdbtypes.h"
  26 #include "f-lang.h"
  27
  28 /* Class for calculating the byte offset for elements within a single
  29    dimension of a Fortran array.  */
  30 class fortran_array_offset_calculator
  31 {
  32 public:
  33   /* Create a new offset calculator for TYPE, which is either an array or a
  34      string.  */
  35   explicit fortran_array_offset_calculator (struct type *type)
  36   {
  37     /* Validate the type.  */
  38     type = check_typedef (type);
  39     if (type->code () != TYPE_CODE_ARRAY
  40         && (type->code () != TYPE_CODE_STRING))
  41       error (_("can only compute offsets for arrays and strings"));
  42
  43     /* Get the range, and extract the bounds.  */
  44     struct type *range_type = type->index_type ();
  45     if (!get_discrete_bounds (range_type, &m_lowerbound, &m_upperbound))
  46       error ("unable to read array bounds");
  47
  48     /* Figure out the stride for this array.  */
  49     struct type *elt_type = check_typedef (TYPE_TARGET_TYPE (type));
  50     m_stride = type->index_type ()->bounds ()->bit_stride ();
  51     if (m_stride == 0)
  52       m_stride = type_length_units (elt_type);
  53     else
  54       {
  55         int unit_size
  56           = gdbarch_addressable_memory_unit_size (elt_type->arch ());
  57         m_stride /= (unit_size * 8);
  58       }
  59   };
  60
  61   /* Get the byte offset for element INDEX within the type we are working
  62      on.  There is no bounds checking done on INDEX.  If the stride is
  63      negative then we still assume that the base address (for the array
  64      object) points to the element with the lowest memory address, we then
  65      calculate an offset assuming that index 0 will be the element at the
  66      highest address, index 1 the next highest, and so on.  This is not
  67      quite how Fortran works in reality; in reality the base address of
  68      the object would point at the element with the highest address, and
  69      we would index backwards from there in the "normal" way, however,
  70      GDB's current value contents model doesn't support having the base
  71      address be near to the end of the value contents, so we currently
  72      adjust the base address of Fortran arrays with negative strides so
  73      their base address points at the lowest memory address.  This code
  74      here is part of working around this weirdness.  */
  75   LONGEST index_offset (LONGEST index)
  76   {
  77     LONGEST offset;
  78     if (m_stride < 0)
  79       offset = std::abs (m_stride) * (m_upperbound - index);
  80     else
  81       offset = std::abs (m_stride) * (index - m_lowerbound);
  82     return offset;
  83   }
  84
  85 private:
  86
  87   /* The stride for the type we are working with.  */
  88   LONGEST m_stride;
  89
  90   /* The upper bound for the type we are working with.  */
  91   LONGEST m_upperbound;
  92
  93   /* The lower bound for the type we are working with.  */
  94   LONGEST m_lowerbound;
  95 };
  96
  97 /* A base class used by fortran_array_walker.  There's no virtual methods
  98    here, sub-classes should just override the functions they want in order
  99    to specialise the behaviour to their needs.  The functionality
 100    provided in these default implementations will visit every array
 101    element, but do nothing for each element.  */
 102
 103 struct fortran_array_walker_base_impl
 104 {
 105   /* Called when iterating between the lower and upper bounds of each
 106      dimension of the array.  Return true if GDB should continue iterating,
 107      otherwise, return false.
 108
 109      SHOULD_CONTINUE indicates if GDB is going to stop anyway, and should
 110      be taken into consideration when deciding what to return.  If
 111      SHOULD_CONTINUE is false then this function must also return false,
 112      the function is still called though in case extra work needs to be
 113      done as part of the stopping process.  */
 114   bool continue_walking (bool should_continue)
 115   { return should_continue; }
 116
 117   /* Called when GDB starts iterating over a dimension of the array.  The
 118      argument INDEX_TYPE is the type of the index used to address elements
 119      in the dimension, NELTS holds the number of the elements there, and
 120      INNER_P is true for the inner most dimension (the dimension containing
 121      the actual elements of the array), and false for more outer dimensions.
 122      For a concrete example of how this function is called see the comment
 123      on process_element below.  */
 124   void start_dimension (struct type *index_type, LONGEST nelts, bool inner_p)
 125   { /* Nothing.  */ }
 126
 127   /* Called when GDB finishes iterating over a dimension of the array.  The
 128      argument INNER_P is true for the inner most dimension (the dimension
 129      containing the actual elements of the array), and false for more outer
 130      dimensions.  LAST_P is true for the last call at a particular
 131      dimension.  For a concrete example of how this function is called
 132      see the comment on process_element below.  */
 133   void finish_dimension (bool inner_p, bool last_p)
 134   { /* Nothing.  */ }
 135
 136   /* Called when processing dimensions of the array other than the
 137      innermost one.  WALK_1 is the walker to normally call, ELT_TYPE is
 138      the type of the element being extracted, and ELT_OFF is the offset
 139      of the element from the start of array being walked.  INDEX is the
 140      value of the index the current element is at in the upper dimension.
 141      Finally LAST_P is true only when this is the last element that will
 142      be processed in this dimension.  */
 143   void process_dimension (gdb::function_view<void (struct type *,
 144                                                    int, bool)> walk_1,
 145                           struct type *elt_type, LONGEST elt_off,
 146                           LONGEST index, bool last_p)
 147   {
 148     walk_1 (elt_type, elt_off, last_p);
 149   }
 150
 151   /* Called when processing the inner most dimension of the array, for
 152      every element in the array.  ELT_TYPE is the type of the element being
 153      extracted, and ELT_OFF is the offset of the element from the start of
 154      array being walked.  INDEX is the value of the index the current
 155      element is at in the upper dimension.  Finally LAST_P is true only
 156      when this is the last element that will be processed in this dimension.
 157
 158      Given this two dimensional array ((1, 2) (3, 4) (5, 6)), the calls to
 159      start_dimension, process_element, and finish_dimension look like this:
 160
 161      start_dimension (INDEX_TYPE, 3, false);
 162        start_dimension (INDEX_TYPE, 2, true);
 163          process_element (TYPE, OFFSET, false);
 164          process_element (TYPE, OFFSET, true);
 165        finish_dimension (true, false);
 166        start_dimension (INDEX_TYPE, 2, true);
 167          process_element (TYPE, OFFSET, false);
 168          process_element (TYPE, OFFSET, true);
 169        finish_dimension (true, true);
 170        start_dimension (INDEX_TYPE, 2, true);
 171          process_element (TYPE, OFFSET, false);
 172          process_element (TYPE, OFFSET, true);
 173        finish_dimension (true, true);
 174      finish_dimension (false, true);  */
 175   void process_element (struct type *elt_type, LONGEST elt_off,
 176                         LONGEST index, bool last_p)
 177   { /* Nothing.  */ }
 178 };
 179
 180 /* A class to wrap up the process of iterating over a multi-dimensional
 181    Fortran array.  IMPL is used to specialise what happens as we walk over
 182    the array.  See class FORTRAN_ARRAY_WALKER_BASE_IMPL (above) for the
 183    methods than can be used to customise the array walk.  */
 184 template<typename Impl>
 185 class fortran_array_walker
 186 {
 187   /* Ensure that Impl is derived from the required base class.  This just
 188      ensures that all of the required API methods are available and have a
 189      sensible default implementation.  */
 190   gdb_static_assert ((std::is_base_of<fortran_array_walker_base_impl,Impl>::value));
 191
 192 public:
 193   /* Create a new array walker.  TYPE is the type of the array being walked
 194      over, and ADDRESS is the base address for the object of TYPE in
 195      memory.  All other arguments are forwarded to the constructor of the
 196      template parameter class IMPL.  */
 197   template <typename ...Args>
 198   fortran_array_walker (struct type *type, CORE_ADDR address,
 199                         Args... args)
 200     : m_type (type),
 201       m_address (address),
 202       m_impl (type, address, args...),
 203       m_ndimensions (calc_f77_array_dims (m_type)),
 204       m_nss (0)
 205   { /* Nothing.  */ }
 206
 207   /* Walk the array.  */
 208   void
 209   walk ()
 210   {
 211     walk_1 (m_type, 0, false);
 212   }
 213
 214 private:
 215   /* The core of the array walking algorithm.  TYPE is the type of
 216      the current dimension being processed and OFFSET is the offset
 217      (in bytes) for the start of this dimension.  */
 218   void
 219   walk_1 (struct type *type, int offset, bool last_p)
 220   {
 221     /* Extract the range, and get lower and upper bounds.  */
 222     struct type *range_type = check_typedef (type)->index_type ();
 223     LONGEST lowerbound, upperbound;
 224     if (!get_discrete_bounds (range_type, &lowerbound, &upperbound))
 225       error ("failed to get range bounds");
 226
 227     /* CALC is used to calculate the offsets for each element in this
 228        dimension.  */
 229     fortran_array_offset_calculator calc (type);
 230
 231     m_nss++;
 232     gdb_assert (range_type->code () == TYPE_CODE_RANGE);
 233     m_impl.start_dimension (TYPE_TARGET_TYPE (range_type),
 234                             upperbound - lowerbound + 1,
 235                             m_nss == m_ndimensions);
 236
 237     if (m_nss != m_ndimensions)
 238       {
 239         struct type *subarray_type = TYPE_TARGET_TYPE (check_typedef (type));
 240
 241         /* For dimensions other than the inner most, walk each element and
 242            recurse while peeling off one more dimension of the array.  */
 243         for (LONGEST i = lowerbound;
 244              m_impl.continue_walking (i < upperbound + 1);
 245              i++)
 246           {
 247             /* Use the index and the stride to work out a new offset.  */
 248             LONGEST new_offset = offset + calc.index_offset (i);
 249
 250             /* Now print the lower dimension.  */
 251             m_impl.process_dimension
 252               ([this] (struct type *w_type, int w_offset, bool w_last_p) -> void
 253                 {
 254                   this->walk_1 (w_type, w_offset, w_last_p);
 255                 },
 256                subarray_type, new_offset, i, i == upperbound);
 257           }
 258       }
 259     else
 260       {
 261         struct type *elt_type = check_typedef (TYPE_TARGET_TYPE (type));
 262
 263         /* For the inner most dimension of the array, process each element
 264            within this dimension.  */
 265         for (LONGEST i = lowerbound;
 266              m_impl.continue_walking (i < upperbound + 1);
 267              i++)
 268           {
 269             LONGEST elt_off = offset + calc.index_offset (i);
 270
 271             if (is_dynamic_type (elt_type))
 272               {
 273                 CORE_ADDR e_address = m_address + elt_off;
 274                 elt_type = resolve_dynamic_type (elt_type, {}, e_address);
 275               }
 276
 277             m_impl.process_element (elt_type, elt_off, i, i == upperbound);
 278           }
 279       }
 280
 281     m_impl.finish_dimension (m_nss == m_ndimensions, last_p || m_nss == 1);
 282     m_nss--;
 283   }
 284
 285   /* The array type being processed.  */
 286   struct type *m_type;
 287
 288   /* The address in target memory for the object of M_TYPE being
 289      processed.  This is required in order to resolve dynamic types.  */
 290   CORE_ADDR m_address;
 291
 292   /* An instance of the template specialisation class.  */
 293   Impl m_impl;
 294
 295   /* The total number of dimensions in M_TYPE.  */
 296   int m_ndimensions;
 297
 298   /* The current dimension number being processed.  */
 299   int m_nss;
 300 };
 301
 302 #endif /* F_ARRAY_WALKER_H */