2 * include/linker_lists.h
4 * Implementation of linker-generated arrays
6 * Copyright (C) 2012 Marek Vasut <marex@denx.de>
8 * SPDX-License-Identifier: GPL-2.0+
11 #ifndef __LINKER_LISTS_H__
12 #define __LINKER_LISTS_H__
14 #include <linux/compiler.h>
17 * There is no use in including this from ASM files, but that happens
18 * anyway, e.g. PPC kgdb.S includes command.h which incluse us.
19 * So just don't define anything when included from ASM.
22 #if !defined(__ASSEMBLY__)
25 * A linker list is constructed by grouping together linker input
26 * sections, each containning one entry of the list. Each input section
27 * contains a constant initialized variable which holds the entry's
28 * content. Linker list input sections are constructed from the list
29 * and entry names, plus a prefix which allows grouping all lists
30 * together. Assuming _list and _entry are the list and entry names,
31 * then the corresponding input section name is
33 * .u_boot_list_ + 2_ + @_list + _2_ + @_entry
35 * and the C variable name is
37 * _u_boot_list + _2_ + @_list + _2_ + @_entry
39 * This ensures uniqueness for both input section and C variable name.
41 * Note that the names differ only in the first character, "." for the
42 * setion and "_" for the variable, so that the linker cannot confuse
43 * section and symbol names. From now on, both names will be referred
46 * %u_boot_list_ + 2_ + @_list + _2_ + @_entry
48 * Entry variables need never be referred to directly.
50 * The naming scheme for input sections allows grouping all linker lists
51 * into a single linker output section and grouping all entries for a
54 * Note the two '_2_' constant components in the names: their presence
55 * allows putting a start and end symbols around a list, by mapping
56 * these symbols to sections names with components "1" (before) and
57 * "3" (after) instead of "2" (within).
58 * Start and end symbols for a list can generally be defined as
60 * %u_boot_list_2_ + @_list + _1_...
61 * %u_boot_list_2_ + @_list + _3_...
63 * Start and end symbols for the whole of the linker lists area can be
69 * Here is an example of the sorted sections which result from a list
70 * "array" made up of three entries : "first", "second" and "third",
71 * iterated at least once.
73 * .u_boot_list_2_array_1
74 * .u_boot_list_2_array_2_first
75 * .u_boot_list_2_array_2_second
76 * .u_boot_list_2_array_2_third
77 * .u_boot_list_2_array_3
79 * If lists must be divided into sublists (e.g. for iterating only on
80 * part of a list), one can simply give the list a name of the form
81 * 'outer_2_inner', where 'outer' is the global list name and 'inner'
82 * is the sub-list name. Iterators for the whole list should use the
83 * global list name ("outer"); iterators for only a sub-list should use
84 * the full sub-list name ("outer_2_inner").
86 * Here is an example of the sections generated from a global list
87 * named "drivers", two sub-lists named "i2c" and "pci", and iterators
88 * defined for the whole list and each sub-list:
90 * %u_boot_list_2_drivers_1
91 * %u_boot_list_2_drivers_2_i2c_1
92 * %u_boot_list_2_drivers_2_i2c_2_first
93 * %u_boot_list_2_drivers_2_i2c_2_first
94 * %u_boot_list_2_drivers_2_i2c_2_second
95 * %u_boot_list_2_drivers_2_i2c_2_third
96 * %u_boot_list_2_drivers_2_i2c_3
97 * %u_boot_list_2_drivers_2_pci_1
98 * %u_boot_list_2_drivers_2_pci_2_first
99 * %u_boot_list_2_drivers_2_pci_2_second
100 * %u_boot_list_2_drivers_2_pci_2_third
101 * %u_boot_list_2_drivers_2_pci_3
102 * %u_boot_list_2_drivers_3
106 * ll_entry_declare() - Declare linker-generated array entry
107 * @_type: Data type of the entry
108 * @_name: Name of the entry
109 * @_list: name of the list. Should contain only characters allowed
110 * in a C variable name!
112 * This macro declares a variable that is placed into a linker-generated
113 * array. This is a basic building block for more advanced use of linker-
114 * generated arrays. The user is expected to build their own macro wrapper
117 * A variable declared using this macro must be compile-time initialized.
119 * Special precaution must be made when using this macro:
121 * 1) The _type must not contain the "static" keyword, otherwise the
122 * entry is generated and can be iterated but is listed in the map
123 * file and cannot be retrieved by name.
125 * 2) In case a section is declared that contains some array elements AND
126 * a subsection of this section is declared and contains some elements,
127 * it is imperative that the elements are of the same type.
129 * 4) In case an outer section is declared that contains some array elements
130 * AND an inner subsection of this section is declared and contains some
131 * elements, then when traversing the outer section, even the elements of
132 * the inner sections are present in the array.
135 * ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub, cmd.sub) = {
140 #define ll_entry_declare(_type, _name, _list) \
141 _type _u_boot_list_2_##_list##_2_##_name __aligned(4) \
142 __attribute__((unused, \
143 section(".u_boot_list_2_"#_list"_2_"#_name)))
146 * We need a 0-byte-size type for iterator symbols, and the compiler
147 * does not allow defining objects of C type 'void'. Using an empty
148 * struct is allowed by the compiler, but causes gcc versions 4.4 and
149 * below to complain about aliasing. Therefore we use the next best
150 * thing: zero-sized arrays, which are both 0-byte-size and exempt from
155 * ll_entry_start() - Point to first entry of linker-generated array
156 * @_type: Data type of the entry
157 * @_list: Name of the list in which this entry is placed
159 * This function returns (_type *) pointer to the very first entry of a
160 * linker-generated array placed into subsection of .u_boot_list section
161 * specified by _list argument.
163 * Since this macro defines an array start symbol, its leftmost index
164 * must be 2 and its rightmost index must be 1.
167 * struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
169 #define ll_entry_start(_type, _list) \
171 static char start[0] __aligned(4) __attribute__((unused, \
172 section(".u_boot_list_2_"#_list"_1"))); \
177 * ll_entry_end() - Point after last entry of linker-generated array
178 * @_type: Data type of the entry
179 * @_list: Name of the list in which this entry is placed
180 * (with underscores instead of dots)
182 * This function returns (_type *) pointer after the very last entry of
183 * a linker-generated array placed into subsection of .u_boot_list
184 * section specified by _list argument.
186 * Since this macro defines an array end symbol, its leftmost index
187 * must be 2 and its rightmost index must be 3.
190 * struct my_sub_cmd *msc = ll_entry_end(struct my_sub_cmd, cmd_sub);
192 #define ll_entry_end(_type, _list) \
194 static char end[0] __aligned(4) __attribute__((unused, \
195 section(".u_boot_list_2_"#_list"_3"))); \
199 * ll_entry_count() - Return the number of elements in linker-generated array
200 * @_type: Data type of the entry
201 * @_list: Name of the list of which the number of elements is computed
203 * This function returns the number of elements of a linker-generated array
204 * placed into subsection of .u_boot_list section specified by _list
205 * argument. The result is of an unsigned int type.
209 * const unsigned int count = ll_entry_count(struct my_sub_cmd, cmd_sub);
210 * struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
211 * for (i = 0; i < count; i++, msc++)
212 * printf("Entry %i, x=%i y=%i\n", i, msc->x, msc->y);
214 #define ll_entry_count(_type, _list) \
216 _type *start = ll_entry_start(_type, _list); \
217 _type *end = ll_entry_end(_type, _list); \
218 unsigned int _ll_result = end - start; \
223 * ll_entry_get() - Retrieve entry from linker-generated array by name
224 * @_type: Data type of the entry
225 * @_name: Name of the entry
226 * @_list: Name of the list in which this entry is placed
228 * This function returns a pointer to a particular entry in LG-array
229 * identified by the subsection of u_boot_list where the entry resides
233 * ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
238 * struct my_sub_cmd *c = ll_entry_get(struct my_sub_cmd, my_sub_cmd, cmd_sub);
240 #define ll_entry_get(_type, _name, _list) \
242 extern _type _u_boot_list_2_##_list##_2_##_name; \
243 _type *_ll_result = \
244 &_u_boot_list_2_##_list##_2_##_name; \
249 * ll_start() - Point to first entry of first linker-generated array
250 * @_type: Data type of the entry
252 * This function returns (_type *) pointer to the very first entry of
253 * the very first linker-generated array.
255 * Since this macro defines the start of the linker-generated arrays,
256 * its leftmost index must be 1.
259 * struct my_sub_cmd *msc = ll_start(struct my_sub_cmd);
261 #define ll_start(_type) \
263 static char start[0] __aligned(4) __attribute__((unused, \
264 section(".u_boot_list_1"))); \
269 * ll_entry_end() - Point after last entry of last linker-generated array
270 * @_type: Data type of the entry
272 * This function returns (_type *) pointer after the very last entry of
273 * the very last linker-generated array.
275 * Since this macro defines the end of the linker-generated arrays,
276 * its leftmost index must be 3.
279 * struct my_sub_cmd *msc = ll_end(struct my_sub_cmd);
281 #define ll_end(_type) \
283 static char end[0] __aligned(4) __attribute__((unused, \
284 section(".u_boot_list_3"))); \
288 #endif /* __ASSEMBLY__ */
290 #endif /* __LINKER_LISTS_H__ */