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