include/linker_lists.h

   1 /* SPDX-License-Identifier: GPL-2.0+ */
   2 /*
   3  * include/linker_lists.h
   4  *
   5  * Implementation of linker-generated arrays
   6  *
   7  * Copyright (C) 2012 Marek Vasut <marex@denx.de>
   8  */
   9
  10 #ifndef __LINKER_LISTS_H__
  11 #define __LINKER_LISTS_H__
  12
  13 #include <linux/compiler.h>
  14
  15 /*
  16  * There is no use in including this from ASM files.
  17  * So just don't define anything when included from ASM.
  18  */
  19
  20 #if !defined(__ASSEMBLY__)
  21
  22 /**
  23  * A linker list is constructed by grouping together linker input
  24  * sections, each containing one entry of the list. Each input section
  25  * contains a constant initialized variable which holds the entry's
  26  * content. Linker list input sections are constructed from the list
  27  * and entry names, plus a prefix which allows grouping all lists
  28  * together. Assuming _list and _entry are the list and entry names,
  29  * then the corresponding input section name is
  30  *
  31  *   .u_boot_list_ + 2_ + @_list + _2_ + @_entry
  32  *
  33  * and the C variable name is
  34  *
  35  *   _u_boot_list + _2_ + @_list + _2_ + @_entry
  36  *
  37  * This ensures uniqueness for both input section and C variable name.
  38  *
  39  * Note that the names differ only in the first character, "." for the
  40  * section and "_" for the variable, so that the linker cannot confuse
  41  * section and symbol names. From now on, both names will be referred
  42  * to as
  43  *
  44  *   %u_boot_list_ + 2_ + @_list + _2_ + @_entry
  45  *
  46  * Entry variables need never be referred to directly.
  47  *
  48  * The naming scheme for input sections allows grouping all linker lists
  49  * into a single linker output section and grouping all entries for a
  50  * single list.
  51  *
  52  * Note the two '_2_' constant components in the names: their presence
  53  * allows putting a start and end symbols around a list, by mapping
  54  * these symbols to sections names with components "1" (before) and
  55  * "3" (after) instead of "2" (within).
  56  * Start and end symbols for a list can generally be defined as
  57  *
  58  *   %u_boot_list_2_ + @_list + _1_...
  59  *   %u_boot_list_2_ + @_list + _3_...
  60  *
  61  * Start and end symbols for the whole of the linker lists area can be
  62  * defined as
  63  *
  64  *   %u_boot_list_1_...
  65  *   %u_boot_list_3_...
  66  *
  67  * Here is an example of the sorted sections which result from a list
  68  * "array" made up of three entries : "first", "second" and "third",
  69  * iterated at least once.
  70  *
  71  *   .u_boot_list_2_array_1
  72  *   .u_boot_list_2_array_2_first
  73  *   .u_boot_list_2_array_2_second
  74  *   .u_boot_list_2_array_2_third
  75  *   .u_boot_list_2_array_3
  76  *
  77  * If lists must be divided into sublists (e.g. for iterating only on
  78  * part of a list), one can simply give the list a name of the form
  79  * 'outer_2_inner', where 'outer' is the global list name and 'inner'
  80  * is the sub-list name. Iterators for the whole list should use the
  81  * global list name ("outer"); iterators for only a sub-list should use
  82  * the full sub-list name ("outer_2_inner").
  83  *
  84  * Here is an example of the sections generated from a global list
  85  * named "drivers", two sub-lists named "i2c" and "pci", and iterators
  86  * defined for the whole list and each sub-list:
  87  *
  88  *   %u_boot_list_2_drivers_1
  89  *   %u_boot_list_2_drivers_2_i2c_1
  90  *   %u_boot_list_2_drivers_2_i2c_2_first
  91  *   %u_boot_list_2_drivers_2_i2c_2_first
  92  *   %u_boot_list_2_drivers_2_i2c_2_second
  93  *   %u_boot_list_2_drivers_2_i2c_2_third
  94  *   %u_boot_list_2_drivers_2_i2c_3
  95  *   %u_boot_list_2_drivers_2_pci_1
  96  *   %u_boot_list_2_drivers_2_pci_2_first
  97  *   %u_boot_list_2_drivers_2_pci_2_second
  98  *   %u_boot_list_2_drivers_2_pci_2_third
  99  *   %u_boot_list_2_drivers_2_pci_3
 100  *   %u_boot_list_2_drivers_3
 101  */
 102
 103 /**
 104  * llsym() - Access a linker-generated array entry
 105  * @_type:      Data type of the entry
 106  * @_name:      Name of the entry
 107  * @_list:      name of the list. Should contain only characters allowed
 108  *              in a C variable name!
 109  */
 110 #define llsym(_type, _name, _list) \
 111                 ((_type *)&_u_boot_list_2_##_list##_2_##_name)
 112
 113 /**
 114  * ll_entry_declare() - Declare linker-generated array entry
 115  * @_type:      Data type of the entry
 116  * @_name:      Name of the entry
 117  * @_list:      name of the list. Should contain only characters allowed
 118  *              in a C variable name!
 119  *
 120  * This macro declares a variable that is placed into a linker-generated
 121  * array. This is a basic building block for more advanced use of linker-
 122  * generated arrays. The user is expected to build their own macro wrapper
 123  * around this one.
 124  *
 125  * A variable declared using this macro must be compile-time initialized.
 126  *
 127  * Special precaution must be made when using this macro:
 128  *
 129  * 1) The _type must not contain the "static" keyword, otherwise the
 130  *    entry is generated and can be iterated but is listed in the map
 131  *    file and cannot be retrieved by name.
 132  *
 133  * 2) In case a section is declared that contains some array elements AND
 134  *    a subsection of this section is declared and contains some elements,
 135  *    it is imperative that the elements are of the same type.
 136  *
 137  * 4) In case an outer section is declared that contains some array elements
 138  *    AND an inner subsection of this section is declared and contains some
 139  *    elements, then when traversing the outer section, even the elements of
 140  *    the inner sections are present in the array.
 141  *
 142  * Example:
 143  * ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
 144  *         .x = 3,
 145  *         .y = 4,
 146  * };
 147  */
 148 #define ll_entry_declare(_type, _name, _list)                           \
 149         _type _u_boot_list_2_##_list##_2_##_name __aligned(4)           \
 150                         __attribute__((unused,                          \
 151                         section(".u_boot_list_2_"#_list"_2_"#_name)))
 152
 153 /**
 154  * ll_entry_declare_list() - Declare a list of link-generated array entries
 155  * @_type:      Data type of each entry
 156  * @_name:      Name of the entry
 157  * @_list:      name of the list. Should contain only characters allowed
 158  *              in a C variable name!
 159  *
 160  * This is like ll_entry_declare() but creates multiple entries. It should
 161  * be assigned to an array.
 162  *
 163  * ll_entry_declare_list(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
 164  *      { .x = 3, .y = 4 },
 165  *      { .x = 8, .y = 2 },
 166  *      { .x = 1, .y = 7 }
 167  * };
 168  */
 169 #define ll_entry_declare_list(_type, _name, _list)                      \
 170         _type _u_boot_list_2_##_list##_2_##_name[] __aligned(4)         \
 171                         __attribute__((unused,                          \
 172                         section(".u_boot_list_2_"#_list"_2_"#_name)))
 173
 174 /**
 175  * We need a 0-byte-size type for iterator symbols, and the compiler
 176  * does not allow defining objects of C type 'void'. Using an empty
 177  * struct is allowed by the compiler, but causes gcc versions 4.4 and
 178  * below to complain about aliasing. Therefore we use the next best
 179  * thing: zero-sized arrays, which are both 0-byte-size and exempt from
 180  * aliasing warnings.
 181  */
 182
 183 /**
 184  * ll_entry_start() - Point to first entry of linker-generated array
 185  * @_type:      Data type of the entry
 186  * @_list:      Name of the list in which this entry is placed
 187  *
 188  * This function returns (_type *) pointer to the very first entry of a
 189  * linker-generated array placed into subsection of .u_boot_list section
 190  * specified by _list argument.
 191  *
 192  * Since this macro defines an array start symbol, its leftmost index
 193  * must be 2 and its rightmost index must be 1.
 194  *
 195  * Example:
 196  * struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
 197  */
 198 #define ll_entry_start(_type, _list)                                    \
 199 ({                                                                      \
 200         static char start[0] __aligned(4) __attribute__((unused,        \
 201                 section(".u_boot_list_2_"#_list"_1")));                 \
 202         (_type *)&start;                                                \
 203 })
 204
 205 /**
 206  * ll_entry_end() - Point after last entry of linker-generated array
 207  * @_type:      Data type of the entry
 208  * @_list:      Name of the list in which this entry is placed
 209  *              (with underscores instead of dots)
 210  *
 211  * This function returns (_type *) pointer after the very last entry of
 212  * a linker-generated array placed into subsection of .u_boot_list
 213  * section specified by _list argument.
 214  *
 215  * Since this macro defines an array end symbol, its leftmost index
 216  * must be 2 and its rightmost index must be 3.
 217  *
 218  * Example:
 219  * struct my_sub_cmd *msc = ll_entry_end(struct my_sub_cmd, cmd_sub);
 220  */
 221 #define ll_entry_end(_type, _list)                                      \
 222 ({                                                                      \
 223         static char end[0] __aligned(4) __attribute__((unused,          \
 224                 section(".u_boot_list_2_"#_list"_3")));                 \
 225         (_type *)&end;                                                  \
 226 })
 227 /**
 228  * ll_entry_count() - Return the number of elements in linker-generated array
 229  * @_type:      Data type of the entry
 230  * @_list:      Name of the list of which the number of elements is computed
 231  *
 232  * This function returns the number of elements of a linker-generated array
 233  * placed into subsection of .u_boot_list section specified by _list
 234  * argument. The result is of an unsigned int type.
 235  *
 236  * Example:
 237  * int i;
 238  * const unsigned int count = ll_entry_count(struct my_sub_cmd, cmd_sub);
 239  * struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
 240  * for (i = 0; i < count; i++, msc++)
 241  *         printf("Entry %i, x=%i y=%i\n", i, msc->x, msc->y);
 242  */
 243 #define ll_entry_count(_type, _list)                                    \
 244         ({                                                              \
 245                 _type *start = ll_entry_start(_type, _list);            \
 246                 _type *end = ll_entry_end(_type, _list);                \
 247                 unsigned int _ll_result = end - start;                  \
 248                 _ll_result;                                             \
 249         })
 250
 251 /**
 252  * ll_entry_get() - Retrieve entry from linker-generated array by name
 253  * @_type:      Data type of the entry
 254  * @_name:      Name of the entry
 255  * @_list:      Name of the list in which this entry is placed
 256  *
 257  * This function returns a pointer to a particular entry in linker-generated
 258  * array identified by the subsection of u_boot_list where the entry resides
 259  * and it's name.
 260  *
 261  * Example:
 262  * ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
 263  *         .x = 3,
 264  *         .y = 4,
 265  * };
 266  * ...
 267  * struct my_sub_cmd *c = ll_entry_get(struct my_sub_cmd, my_sub_cmd, cmd_sub);
 268  */
 269 #define ll_entry_get(_type, _name, _list)                               \
 270         ({                                                              \
 271                 extern _type _u_boot_list_2_##_list##_2_##_name;        \
 272                 _type *_ll_result =                                     \
 273                         &_u_boot_list_2_##_list##_2_##_name;            \
 274                 _ll_result;                                             \
 275         })
 276
 277 /**
 278  * ll_start() - Point to first entry of first linker-generated array
 279  * @_type:      Data type of the entry
 280  *
 281  * This function returns (_type *) pointer to the very first entry of
 282  * the very first linker-generated array.
 283  *
 284  * Since this macro defines the start of the linker-generated arrays,
 285  * its leftmost index must be 1.
 286  *
 287  * Example:
 288  * struct my_sub_cmd *msc = ll_start(struct my_sub_cmd);
 289  */
 290 #define ll_start(_type)                                                 \
 291 ({                                                                      \
 292         static char start[0] __aligned(4) __attribute__((unused,        \
 293                 section(".u_boot_list_1")));                            \
 294         (_type *)&start;                                                \
 295 })
 296
 297 /**
 298  * ll_end() - Point after last entry of last linker-generated array
 299  * @_type:      Data type of the entry
 300  *
 301  * This function returns (_type *) pointer after the very last entry of
 302  * the very last linker-generated array.
 303  *
 304  * Since this macro defines the end of the linker-generated arrays,
 305  * its leftmost index must be 3.
 306  *
 307  * Example:
 308  * struct my_sub_cmd *msc = ll_end(struct my_sub_cmd);
 309  */
 310 #define ll_end(_type)                                                   \
 311 ({                                                                      \
 312         static char end[0] __aligned(4) __attribute__((unused,          \
 313                 section(".u_boot_list_3")));                            \
 314         (_type *)&end;                                                  \
 315 })
 316
 317 #endif /* __ASSEMBLY__ */
 318
 319 #endif  /* __LINKER_LISTS_H__ */