gdb/f-array-walker.h

   1 /* Copyright (C) 2020-2021 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 INNER_P is true for the inner most dimension (the dimension
 119      containing the actual elements of the array), and false for more outer
 120      dimensions.  For a concrete example of how this function is called
 121      see the comment on process_element below.  */
 122   void start_dimension (bool inner_p)
 123   { /* Nothing.  */ }
 124
 125   /* Called when GDB finishes iterating over a dimension of the array.  The
 126      argument INNER_P is true for the inner most dimension (the dimension
 127      containing the actual elements of the array), and false for more outer
 128      dimensions.  LAST_P is true for the last call at a particular
 129      dimension.  For a concrete example of how this function is called
 130      see the comment on process_element below.  */
 131   void finish_dimension (bool inner_p, bool last_p)
 132   { /* Nothing.  */ }
 133
 134   /* Called when processing the inner most dimension of the array, for
 135      every element in the array.  ELT_TYPE is the type of the element being
 136      extracted, and ELT_OFF is the offset of the element from the start of
 137      array being walked, and LAST_P is true only when this is the last
 138      element that will be processed in this dimension.
 139
 140      Given this two dimensional array ((1, 2) (3, 4)), the calls to
 141      start_dimension, process_element, and finish_dimension look like this:
 142
 143      start_dimension (false);
 144        start_dimension (true);
 145          process_element (TYPE, OFFSET, false);
 146          process_element (TYPE, OFFSET, true);
 147        finish_dimension (true, false);
 148        start_dimension (true);
 149          process_element (TYPE, OFFSET, false);
 150          process_element (TYPE, OFFSET, true);
 151        finish_dimension (true, true);
 152      finish_dimension (false, true);  */
 153   void process_element (struct type *elt_type, LONGEST elt_off, bool last_p)
 154   { /* Nothing.  */ }
 155 };
 156
 157 /* A class to wrap up the process of iterating over a multi-dimensional
 158    Fortran array.  IMPL is used to specialise what happens as we walk over
 159    the array.  See class FORTRAN_ARRAY_WALKER_BASE_IMPL (above) for the
 160    methods than can be used to customise the array walk.  */
 161 template<typename Impl>
 162 class fortran_array_walker
 163 {
 164   /* Ensure that Impl is derived from the required base class.  This just
 165      ensures that all of the required API methods are available and have a
 166      sensible default implementation.  */
 167   gdb_static_assert ((std::is_base_of<fortran_array_walker_base_impl,Impl>::value));
 168
 169 public:
 170   /* Create a new array walker.  TYPE is the type of the array being walked
 171      over, and ADDRESS is the base address for the object of TYPE in
 172      memory.  All other arguments are forwarded to the constructor of the
 173      template parameter class IMPL.  */
 174   template <typename ...Args>
 175   fortran_array_walker (struct type *type, CORE_ADDR address,
 176                         Args... args)
 177     : m_type (type),
 178       m_address (address),
 179       m_impl (type, address, args...)
 180   {
 181     m_ndimensions =  calc_f77_array_dims (m_type);
 182   }
 183
 184   /* Walk the array.  */
 185   void
 186   walk ()
 187   {
 188     walk_1 (1, m_type, 0, false);
 189   }
 190
 191 private:
 192   /* The core of the array walking algorithm.  NSS is the current
 193      dimension number being processed, TYPE is the type of this dimension,
 194      and OFFSET is the offset (in bytes) for the start of this dimension.  */
 195   void
 196   walk_1 (int nss, struct type *type, int offset, bool last_p)
 197   {
 198     /* Extract the range, and get lower and upper bounds.  */
 199     struct type *range_type = check_typedef (type)->index_type ();
 200     LONGEST lowerbound, upperbound;
 201     if (!get_discrete_bounds (range_type, &lowerbound, &upperbound))
 202       error ("failed to get range bounds");
 203
 204     /* CALC is used to calculate the offsets for each element in this
 205        dimension.  */
 206     fortran_array_offset_calculator calc (type);
 207
 208     m_impl.start_dimension (nss == m_ndimensions);
 209
 210     if (nss != m_ndimensions)
 211       {
 212         /* For dimensions other than the inner most, walk each element and
 213            recurse while peeling off one more dimension of the array.  */
 214         for (LONGEST i = lowerbound;
 215              m_impl.continue_walking (i < upperbound + 1);
 216              i++)
 217           {
 218             /* Use the index and the stride to work out a new offset.  */
 219             LONGEST new_offset = offset + calc.index_offset (i);
 220
 221             /* Now print the lower dimension.  */
 222             struct type *subarray_type
 223               = TYPE_TARGET_TYPE (check_typedef (type));
 224             walk_1 (nss + 1, subarray_type, new_offset, (i == upperbound));
 225           }
 226       }
 227     else
 228       {
 229         /* For the inner most dimension of the array, process each element
 230            within this dimension.  */
 231         for (LONGEST i = lowerbound;
 232              m_impl.continue_walking (i < upperbound + 1);
 233              i++)
 234           {
 235             LONGEST elt_off = offset + calc.index_offset (i);
 236
 237             struct type *elt_type = check_typedef (TYPE_TARGET_TYPE (type));
 238             if (is_dynamic_type (elt_type))
 239               {
 240                 CORE_ADDR e_address = m_address + elt_off;
 241                 elt_type = resolve_dynamic_type (elt_type, {}, e_address);
 242               }
 243
 244             m_impl.process_element (elt_type, elt_off, (i == upperbound));
 245           }
 246       }
 247
 248     m_impl.finish_dimension (nss == m_ndimensions, last_p || nss == 1);
 249   }
 250
 251   /* The array type being processed.  */
 252   struct type *m_type;
 253
 254   /* The address in target memory for the object of M_TYPE being
 255      processed.  This is required in order to resolve dynamic types.  */
 256   CORE_ADDR m_address;
 257
 258   /* An instance of the template specialisation class.  */
 259   Impl m_impl;
 260
 261   /* The total number of dimensions in M_TYPE.  */
 262   int m_ndimensions;
 263 };
 264
 265 #endif /* F_ARRAY_WALKER_H */