include/linker_lists.h

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