1 | .. comment SPDX-License-Identifier: CC-BY-SA-4.0 |
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2 | |
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3 | .. COMMENT: COPYRIGHT (c) 1989-2014. |
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4 | .. COMMENT: On-Line Applications Research Corporation (OAR). |
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5 | .. COMMENT: All rights reserved. |
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6 | |
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7 | .. _Linker Sets: |
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8 | |
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9 | Linker Sets |
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10 | *********** |
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11 | |
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12 | .. index:: linkersets |
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13 | |
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14 | Introduction |
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15 | ============ |
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16 | |
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17 | Linker sets are a flexible means to create arrays of items out of a set of |
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18 | object files at link-time. For example its possible to define an item *I* of |
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19 | type *T* in object file *A* and an item *J* of type *T* in object file *B* to |
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20 | be a member of a linker set *S*. The linker will then collect these two items |
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21 | *I* and *J* and place them in consecutive memory locations, so that they can be |
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22 | accessed like a normal array defined in one object file. The size of a linker |
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23 | set is defined by its begin and end markers. A linker set may be empty. It |
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24 | should only contain items of the same type. |
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25 | |
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26 | The following macros are provided to create, populate and use linker sets. |
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27 | |
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28 | - RTEMS_LINKER_SET_BEGIN_ - Designator of the linker set begin marker |
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29 | |
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30 | - RTEMS_LINKER_SET_END_ - Designator of the linker set end marker |
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31 | |
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32 | - RTEMS_LINKER_SET_SIZE_ - The linker set size in characters |
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33 | |
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34 | - RTEMS_LINKER_SET_ITEM_COUNT_ - The linker set item count |
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35 | |
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36 | - RTEMS_LINKER_SET_IS_EMPTY_ - Is the linker set empty? |
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37 | |
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38 | - RTEMS_LINKER_SET_FOREACH_ - Iterate through the linker set items |
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39 | |
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40 | - RTEMS_LINKER_ROSET_DECLARE_ - Declares a read-only linker set |
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41 | |
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42 | - RTEMS_LINKER_ROSET_ - Defines a read-only linker set |
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43 | |
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44 | - RTEMS_LINKER_ROSET_ITEM_DECLARE_ - Declares a read-only linker set item |
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45 | |
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46 | - RTEMS_LINKER_ROSET_ITEM_REFERENCE_ - References a read-only linker set item |
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47 | |
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48 | - RTEMS_LINKER_ROSET_ITEM_ - Defines a read-only linker set item |
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49 | |
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50 | - RTEMS_LINKER_ROSET_ITEM_ORDERED_ - Defines an ordered read-only linker set item |
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51 | |
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52 | - RTEMS_LINKER_RWSET_DECLARE_ - Declares a read-write linker set |
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53 | |
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54 | - RTEMS_LINKER_RWSET_ - Defines a read-write linker set |
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55 | |
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56 | - RTEMS_LINKER_RWSET_ITEM_DECLARE_ - Declares a read-write linker set item |
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57 | |
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58 | - RTEMS_LINKER_RWSET_ITEM_REFERENCE_ - References a read-write linker set item |
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59 | |
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60 | - RTEMS_LINKER_RWSET_ITEM_ - Defines a read-write linker set item |
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61 | |
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62 | - RTEMS_LINKER_RWSET_ITEM_ORDERED_ - Defines an ordered read-write linker set item |
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63 | |
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64 | Background |
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65 | ========== |
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66 | |
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67 | Linker sets are used not only in RTEMS, but also for example in Linux, in |
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68 | FreeBSD, for the GNU C constructor extension and for global C++ constructors. |
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69 | They provide a space efficient and flexible means to initialize modules. A |
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70 | linker set consists of |
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71 | |
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72 | - dedicated input sections for the linker (e.g. ``.ctors`` and ``.ctors.*`` in |
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73 | the case of global constructors), |
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74 | |
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75 | - a begin marker (e.g. provided by ``crtbegin.o``, and |
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76 | |
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77 | - an end marker (e.g. provided by ``ctrend.o``). |
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78 | |
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79 | A module may place a certain data item into the dedicated input section. The |
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80 | linker will collect all such data items in this section and creates a begin and |
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81 | end marker. The initialization code can then use the begin and end markers to |
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82 | find all the collected data items (e.g. pointers to initialization functions). |
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83 | |
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84 | In the linker command file of the GNU linker we need the following output |
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85 | section descriptions. |
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86 | |
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87 | .. code-block:: c |
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88 | |
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89 | /* To be placed in a read-only memory region */ |
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90 | .rtemsroset : { |
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91 | KEEP (*(SORT(.rtemsroset.*))) |
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92 | } |
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93 | /* To be placed in a read-write memory region */ |
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94 | .rtemsrwset : { |
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95 | KEEP (*(SORT(.rtemsrwset.*))) |
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96 | } |
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97 | |
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98 | The ``KEEP()`` ensures that a garbage collection by the linker will not discard |
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99 | the content of this section. This would normally be the case since the linker |
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100 | set items are not referenced directly. The ``SORT()`` directive sorts the |
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101 | input sections lexicographically. Please note the lexicographical order of the |
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102 | ``.begin``, ``.content`` and ``.end`` section name parts in the RTEMS linker |
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103 | sets macros which ensures that the position of the begin and end markers are |
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104 | right. |
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105 | |
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106 | So, what is the benefit of using linker sets to initialize modules? It can be |
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107 | used to initialize and include only those RTEMS managers and other components |
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108 | which are used by the application. For example, in case an application uses |
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109 | message queues, it must call ``rtems_message_queue_create()``. In the module |
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110 | implementing this function, we can place a linker set item and register the |
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111 | message queue handler constructor. Otherwise, in case the application does not |
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112 | use message queues, there will be no reference to the |
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113 | ``rtems_message_queue_create()`` function and the constructor is not |
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114 | registered, thus nothing of the message queue handler will be in the final |
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115 | executable. |
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116 | |
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117 | For an example see test program :file:`sptests/splinkersets01`. |
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118 | |
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119 | Directives |
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120 | ========== |
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121 | |
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122 | .. raw:: latex |
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123 | |
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124 | \clearpage |
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125 | |
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126 | .. _RTEMS_LINKER_SET_BEGIN: |
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127 | |
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128 | RTEMS_LINKER_SET_BEGIN - Designator of the linker set begin marker |
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129 | ------------------------------------------------------------------ |
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130 | .. index:: RTEMS_LINKER_SET_BEGIN |
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131 | |
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132 | CALLING SEQUENCE: |
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133 | .. code-block:: c |
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134 | |
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135 | type *begin = RTEMS_LINKER_SET_BEGIN( set ); |
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136 | |
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137 | DESCRIPTION: |
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138 | This macro generates the designator of the begin marker of the linker set |
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139 | identified by ``set``. The item at the begin marker address is the first |
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140 | member of the linker set if it exists, e.g. the linker set is not empty. A |
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141 | linker set is empty, if and only if the begin and end markers have the same |
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142 | address. |
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143 | |
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144 | The ``set`` parameter itself must be a valid C designator on which no macro |
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145 | expansion is performed. It uniquely identifies the linker set. |
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146 | |
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147 | NOTE: |
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148 | The compiler may try to be smart. In general it will not work to assign linker |
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149 | set begin and end addresses to pointer variables and treat them like |
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150 | ordinary pointers. The compiler may exploit the fact that actually two |
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151 | distinct objects are involved and use this to optimize. To avoid trouble |
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152 | use :ref:`RTEMS_LINKER_SET_SIZE`, :ref:`RTEMS_LINKER_SET_ITEM_COUNT`, |
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153 | :ref:`RTEMS_LINKER_SET_IS_EMPTY` and :ref:`RTEMS_LINKER_SET_FOREACH`. |
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154 | |
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155 | .. raw:: latex |
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156 | |
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157 | \clearpage |
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158 | |
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159 | .. _RTEMS_LINKER_SET_END: |
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160 | |
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161 | RTEMS_LINKER_SET_END - Designator of the linker set end marker |
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162 | -------------------------------------------------------------- |
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163 | .. index:: RTEMS_LINKER_SET_END |
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164 | |
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165 | CALLING SEQUENCE: |
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166 | .. code-block:: c |
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167 | |
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168 | type *end = RTEMS_LINKER_SET_END( set ); |
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169 | |
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170 | DESCRIPTION: |
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171 | This macro generates the designator of the end marker of the linker set |
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172 | identified by ``set``. The item at the end marker address is not a member |
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173 | of the linker set. The ``set`` parameter itself must be a valid C |
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174 | designator on which no macro expansion is performed. It uniquely |
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175 | identifies the linker set. |
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176 | |
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177 | .. raw:: latex |
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178 | |
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179 | \clearpage |
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180 | |
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181 | .. _RTEMS_LINKER_SET_SIZE: |
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182 | |
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183 | RTEMS_LINKER_SET_SIZE - The linker set size in characters |
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184 | --------------------------------------------------------- |
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185 | .. index:: RTEMS_LINKER_SET_SIZE |
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186 | |
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187 | CALLING SEQUENCE: |
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188 | .. code-block:: c |
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189 | |
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190 | size_t size = RTEMS_LINKER_SET_SIZE( set ); |
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191 | |
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192 | DESCRIPTION: |
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193 | This macro returns the size of the linker set identified by ``set`` in |
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194 | characters. The ``set`` parameter itself must be a valid C designator on |
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195 | which no macro expansion is performed. It uniquely identifies the linker |
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196 | set. |
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197 | |
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198 | .. raw:: latex |
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199 | |
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200 | \clearpage |
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201 | |
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202 | .. _RTEMS_LINKER_SET_ITEM_COUNT: |
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203 | |
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204 | RTEMS_LINKER_SET_ITEM_COUNT - The linker set item count |
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205 | --------------------------------------------------------- |
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206 | .. index:: RTEMS_LINKER_SET_ITEM_COUNT |
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207 | |
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208 | CALLING SEQUENCE: |
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209 | .. code-block:: c |
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210 | |
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211 | size_t item_count = RTEMS_LINKER_SET_ITEM_COUNT( set ); |
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212 | |
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213 | DESCRIPTION: |
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214 | This macro returns the item count of the linker set identified by ``set``. |
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215 | The ``set`` parameter itself must be a valid C designator on which no macro |
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216 | expansion is performed. It uniquely identifies the linker set. |
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217 | |
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218 | .. raw:: latex |
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219 | |
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220 | \clearpage |
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221 | |
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222 | .. _RTEMS_LINKER_SET_IS_EMPTY: |
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223 | |
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224 | RTEMS_LINKER_SET_IS_EMPTY - Is the linker set empty? |
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225 | --------------------------------------------------------- |
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226 | .. index:: RTEMS_LINKER_SET_IS_EMPTY |
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227 | |
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228 | CALLING SEQUENCE: |
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229 | .. code-block:: c |
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230 | |
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231 | bool is_empty = RTEMS_LINKER_SET_IS_EMPTY( set ); |
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232 | |
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233 | DESCRIPTION: |
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234 | This macro returns true if the linker set identified by ``set`` is empty, |
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235 | otherwise returns false. The ``set`` parameter itself must be a valid C |
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236 | designator on which no macro expansion is performed. It uniquely |
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237 | identifies the linker set. |
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238 | |
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239 | .. raw:: latex |
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240 | |
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241 | \clearpage |
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242 | |
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243 | .. _RTEMS_LINKER_SET_FOREACH: |
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244 | |
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245 | RTEMS_LINKER_SET_FOREACH - Iterate through the linker set items |
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246 | --------------------------------------------------------- |
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247 | .. index:: RTEMS_LINKER_SET_FOREACH |
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248 | |
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249 | CALLING SEQUENCE: |
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250 | .. code-block:: c |
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251 | |
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252 | RTEMS_LINKER_RWSET( myset, int ); |
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253 | |
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254 | int count( void ) |
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255 | { |
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256 | int *item; |
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257 | int n; |
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258 | |
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259 | n = 0; |
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260 | RTEMS_LINKER_SET_FOREACH( myset, item ) { |
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261 | n += *item; |
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262 | } |
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263 | |
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264 | return n; |
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265 | } |
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266 | |
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267 | DESCRIPTION: |
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268 | This macro generates a for loop statement which iterates through each item |
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269 | of a linker set identified by ``set``. The ``set`` parameter itself must |
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270 | be a valid C designator on which no macro expansion is performed. It |
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271 | uniquely identifies the linker set. The ``item`` parameter must be a |
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272 | pointer to an item of the linker set. It iterates through all items of the |
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273 | linker set from begin to end. |
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274 | |
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275 | .. raw:: latex |
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276 | |
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277 | \clearpage |
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278 | |
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279 | .. _RTEMS_LINKER_ROSET_DECLARE: |
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280 | |
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281 | RTEMS_LINKER_ROSET_DECLARE - Declares a read-only linker set |
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282 | ------------------------------------------------------------ |
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283 | .. index:: RTEMS_LINKER_ROSET_DECLARE |
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284 | |
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285 | CALLING SEQUENCE: |
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286 | .. code-block:: c |
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287 | |
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288 | RTEMS_LINKER_ROSET_DECLARE( set, type ); |
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289 | |
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290 | DESCRIPTION: |
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291 | This macro generates declarations for the begin and end markers of a |
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292 | read-only linker set identified by ``set``. The ``set`` parameter itself |
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293 | must be a valid C designator on which no macro expansion is performed. It |
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294 | uniquely identifies the linker set. The ``type`` parameter defines the type |
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295 | of the linker set items. The type must be the same for all macro |
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296 | invocations of a particular linker set. |
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297 | |
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298 | .. raw:: latex |
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299 | |
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300 | \clearpage |
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301 | |
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302 | .. _RTEMS_LINKER_ROSET: |
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303 | |
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304 | RTEMS_LINKER_ROSET - Defines a read-only linker set |
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305 | --------------------------------------------------- |
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306 | .. index:: RTEMS_LINKER_ROSET |
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307 | |
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308 | CALLING SEQUENCE: |
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309 | .. code-block:: c |
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310 | |
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311 | RTEMS_LINKER_ROSET( set, type ); |
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312 | |
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313 | DESCRIPTION: |
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314 | This macro generates definitions for the begin and end markers of a |
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315 | read-only linker set identified by ``set``. The ``set`` parameter itself |
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316 | must be a valid C designator on which no macro expansion is performed. It |
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317 | uniquely identifies the linker set. The ``type`` parameter defines the type |
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318 | of the linker set items. The type must be the same for all macro |
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319 | invocations of a particular linker set. |
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320 | |
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321 | .. raw:: latex |
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322 | |
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323 | \clearpage |
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324 | |
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325 | .. _RTEMS_LINKER_ROSET_ITEM_DECLARE: |
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326 | |
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327 | RTEMS_LINKER_ROSET_ITEM_DECLARE - Declares a read-only linker set item |
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328 | ---------------------------------------------------------------------- |
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329 | .. index:: RTEMS_LINKER_ROSET_ITEM_DECLARE |
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330 | |
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331 | CALLING SEQUENCE: |
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332 | .. code-block:: c |
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333 | |
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334 | RTEMS_LINKER_ROSET_ITEM_DECLARE( set, type, item ); |
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335 | |
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336 | DESCRIPTION: |
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337 | This macro generates a declaration of an item contained in the read-only |
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338 | linker set identified by ``set``. The ``set`` parameter itself must be a |
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339 | valid C designator on which no macro expansion is performed. It uniquely |
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340 | identifies the linker set. The ``type`` parameter defines the type of the |
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341 | linker set items. The type must be the same for all macro invocations of a |
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342 | particular linker set. The ``item`` parameter itself must be a valid C |
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343 | designator on which no macro expansion is performed. It uniquely |
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344 | identifies an item in the linker set. |
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345 | |
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346 | .. raw:: latex |
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347 | |
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348 | \clearpage |
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349 | |
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350 | .. _RTEMS_LINKER_ROSET_ITEM_REFERENCE: |
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351 | |
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352 | RTEMS_LINKER_ROSET_ITEM_REFERENCE - References a read-only linker set item |
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353 | -------------------------------------------------------------------------- |
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354 | .. index:: RTEMS_LINKER_ROSET_ITEM_REFERENCE |
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355 | |
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356 | CALLING SEQUENCE: |
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357 | .. code-block:: c |
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358 | |
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359 | RTEMS_LINKER_ROSET_ITEM_REFERENCE( set, type, item ); |
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360 | |
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361 | DESCRIPTION: |
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362 | This macro generates a reference to an item contained in the read-only |
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363 | linker set identified by ``set``. The ``set`` parameter itself must be a |
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364 | valid C designator on which no macro expansion is performed. It uniquely |
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365 | identifies the linker set. The ``type`` parameter defines the type of the |
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366 | linker set items. The type must be the same for all macro invocations of a |
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367 | particular linker set. The ``item`` parameter itself must be a valid C |
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368 | designator on which no macro expansion is performed. It uniquely |
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369 | identifies an item in the linker set. |
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370 | |
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371 | .. raw:: latex |
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372 | |
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373 | \clearpage |
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374 | |
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375 | .. _RTEMS_LINKER_ROSET_ITEM: |
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376 | |
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377 | RTEMS_LINKER_ROSET_ITEM - Defines a read-only linker set item |
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378 | ------------------------------------------------------------- |
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379 | .. index:: RTEMS_LINKER_ROSET_ITEM |
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380 | |
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381 | CALLING SEQUENCE: |
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382 | .. code-block:: c |
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383 | |
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384 | RTEMS_LINKER_ROSET_ITEM( set, type, item ); |
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385 | |
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386 | DESCRIPTION: |
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387 | This macro generates a definition of an item contained in the read-only |
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388 | linker set identified by ``set``. The ``set`` parameter itself must be a |
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389 | valid C designator on which no macro expansion is performed. It uniquely |
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390 | identifies the linker set. The ``type`` parameter defines the type of the |
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391 | linker set items. The type must be the same for all macro invocations of a |
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392 | particular linker set. The ``item`` parameter itself must be a valid C |
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393 | designator on which no macro expansion is performed. It uniquely |
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394 | identifies an item in the linker set. |
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395 | |
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396 | .. raw:: latex |
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397 | |
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398 | \clearpage |
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399 | |
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400 | .. _RTEMS_LINKER_ROSET_ITEM_ORDERED: |
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401 | |
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402 | RTEMS_LINKER_ROSET_ITEM_ORDERED - Defines an ordered read-only linker set item |
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403 | ------------------------------------------------------------------------------ |
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404 | .. index:: RTEMS_LINKER_ROSET_ITEM_ORDERED |
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405 | |
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406 | CALLING SEQUENCE: |
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407 | .. code-block:: c |
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408 | |
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409 | RTEMS_LINKER_ROSET_ITEM_ORDERED( set, type, item, order ); |
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410 | |
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411 | DESCRIPTION: |
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412 | This macro generates a definition of an ordered item contained in the |
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413 | read-only linker set identified by ``set``. The ``set`` parameter itself |
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414 | must be a valid C designator on which no macro expansion is performed. It |
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415 | uniquely identifies the linker set. The ``type`` parameter defines the type |
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416 | of the linker set items. The type must be the same for all macro |
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417 | invocations of a particular linker set. The ``item`` parameter itself must |
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418 | be a valid C designator on which no macro expansion is performed. It |
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419 | uniquely identifies an item in the linker set. The ``order`` parameter must |
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420 | be a valid linker input section name part on which macro expansion is |
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421 | performed. The items are lexicographically ordered according to the |
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422 | ``order`` parameter within a linker set. Ordered items are placed before |
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423 | unordered items in the linker set. |
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424 | |
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425 | NOTES: |
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426 | To be resilient to typos in the order parameter, it is recommended to use |
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427 | the following construct in macros defining items for a particular linker |
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428 | set (see enum in ``XYZ_ITEM()``). |
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429 | |
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430 | .. code-block:: c |
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431 | |
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432 | #include <rtems/linkersets.h> |
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433 | |
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434 | typedef struct { |
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435 | int foo; |
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436 | } xyz_item; |
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437 | |
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438 | /* The XYZ-order defines */ |
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439 | #define XYZ_ORDER_FIRST 0x00001000 |
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440 | #define XYZ_ORDER_AND_SO_ON 0x00002000 |
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441 | |
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442 | /* Defines an ordered XYZ-item */ |
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443 | #define XYZ_ITEM( item, order ) \ |
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444 | enum { xyz_##item = order - order }; \ |
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445 | RTEMS_LINKER_ROSET_ITEM_ORDERED( \ |
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446 | xyz, const xyz_item *, item, order \ |
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447 | ) = { &item } |
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448 | |
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449 | /* Example item */ |
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450 | static const xyz_item some_item = { 123 }; |
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451 | XYZ_ITEM( some_item, XYZ_ORDER_FIRST ); |
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452 | |
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453 | .. raw:: latex |
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454 | |
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455 | \clearpage |
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456 | |
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457 | .. _RTEMS_LINKER_RWSET_DECLARE: |
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458 | |
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459 | RTEMS_LINKER_RWSET_DECLARE - Declares a read-write linker set |
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460 | ------------------------------------------------------------- |
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461 | .. index:: RTEMS_LINKER_RWSET_DECLARE |
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462 | |
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463 | CALLING SEQUENCE: |
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464 | .. code-block:: c |
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465 | |
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466 | RTEMS_LINKER_RWSET_DECLARE( set, type ); |
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467 | |
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468 | DESCRIPTION: |
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469 | This macro generates declarations for the begin and end markers of a |
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470 | read-write linker set identified by ``set``. The ``set`` parameter itself |
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471 | must be a valid C designator on which no macro expansion is performed. It |
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472 | uniquely identifies the linker set. The ``type`` parameter defines the type |
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473 | of the linker set items. The type must be the same for all macro |
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474 | invocations of a particular linker set. |
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475 | |
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476 | .. raw:: latex |
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477 | |
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478 | \clearpage |
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479 | |
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480 | .. _RTEMS_LINKER_RWSET: |
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481 | |
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482 | RTEMS_LINKER_RWSET - Defines a read-write linker set |
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483 | ---------------------------------------------------- |
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484 | .. index:: RTEMS_LINKER_RWSET |
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485 | |
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486 | CALLING SEQUENCE: |
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487 | .. code-block:: c |
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488 | |
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489 | RTEMS_LINKER_RWSET( set, type ); |
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490 | |
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491 | DESCRIPTION: |
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492 | This macro generates definitions for the begin and end markers of a |
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493 | read-write linker set identified by ``set``. The ``set`` parameter itself |
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494 | must be a valid C designator on which no macro expansion is performed. It |
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495 | uniquely identifies the linker set. The ``type`` parameter defines the type |
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496 | of the linker set items. The type must be the same for all macro |
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497 | invocations of a particular linker set. |
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498 | |
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499 | .. raw:: latex |
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500 | |
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501 | \clearpage |
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502 | |
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503 | .. _RTEMS_LINKER_RWSET_ITEM_DECLARE: |
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504 | |
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505 | RTEMS_LINKER_RWSET_ITEM_DECLARE - Declares a read-write linker set item |
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506 | ----------------------------------------------------------------------- |
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507 | .. index:: RTEMS_LINKER_RWSET_ITEM_DECLARE |
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508 | |
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509 | CALLING SEQUENCE: |
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510 | .. code-block:: c |
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511 | |
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512 | RTEMS_LINKER_RWSET_ITEM_DECLARE( set, type, item ); |
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513 | |
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514 | DESCRIPTION: |
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515 | This macro generates a declaration of an item contained in the read-write |
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516 | linker set identified by ``set``. The ``set`` parameter itself must be a |
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517 | valid C designator on which no macro expansion is performed. It uniquely |
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518 | identifies the linker set. The ``type`` parameter defines the type of the |
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519 | linker set items. The type must be the same for all macro invocations of a |
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520 | particular linker set. The ``item`` parameter itself must be a valid C |
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521 | designator on which no macro expansion is performed. It uniquely |
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522 | identifies an item in the linker set. |
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523 | |
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524 | .. raw:: latex |
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525 | |
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526 | \clearpage |
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527 | |
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528 | .. _RTEMS_LINKER_RWSET_ITEM_REFERENCE: |
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529 | |
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530 | RTEMS_LINKER_RWSET_ITEM_REFERENCE - References a read-write linker set item |
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531 | --------------------------------------------------------------------------- |
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532 | .. index:: RTEMS_LINKER_RWSET_ITEM_REFERENCE |
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533 | |
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534 | CALLING SEQUENCE: |
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535 | .. code-block:: c |
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536 | |
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537 | RTEMS_LINKER_RWSET_ITEM_REFERENCE( set, type, item ); |
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538 | |
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539 | DESCRIPTION: |
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540 | This macro generates a reference to an item contained in the read-write |
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541 | linker set identified by ``set``. The ``set`` parameter itself must be a |
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542 | valid C designator on which no macro expansion is performed. It uniquely |
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543 | identifies the linker set. The ``type`` parameter defines the type of the |
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544 | linker set items. The type must be the same for all macro invocations of a |
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545 | particular linker set. The ``item`` parameter itself must be a valid C |
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546 | designator on which no macro expansion is performed. It uniquely |
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547 | identifies an item in the linker set. |
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548 | |
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549 | .. raw:: latex |
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550 | |
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551 | \clearpage |
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552 | |
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553 | .. _RTEMS_LINKER_RWSET_ITEM: |
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554 | |
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555 | RTEMS_LINKER_RWSET_ITEM - Defines a read-write linker set item |
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556 | -------------------------------------------------------------- |
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557 | .. index:: RTEMS_LINKER_RWSET_ITEM |
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558 | |
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559 | CALLING SEQUENCE: |
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560 | .. code-block:: c |
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561 | |
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562 | RTEMS_LINKER_RWSET_ITEM( set, type, item ); |
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563 | |
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564 | DESCRIPTION: |
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565 | This macro generates a definition of an item contained in the read-write |
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566 | linker set identified by ``set``. The ``set`` parameter itself must be a |
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567 | valid C designator on which no macro expansion is performed. It uniquely |
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568 | identifies the linker set. The ``type`` parameter defines the type of the |
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569 | linker set items. The type must be the same for all macro invocations of a |
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570 | particular linker set. The ``item`` parameter itself must be a valid C |
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571 | designator on which no macro expansion is performed. It uniquely |
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572 | identifies an item in the linker set. |
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573 | |
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574 | .. raw:: latex |
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575 | |
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576 | \clearpage |
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577 | |
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578 | .. _RTEMS_LINKER_RWSET_ITEM_ORDERED: |
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579 | |
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580 | RTEMS_LINKER_RWSET_ITEM_ORDERED - Defines an ordered read-write linker set item |
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581 | ------------------------------------------------------------------------------- |
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582 | .. index:: RTEMS_LINKER_RWSET_ITEM_ORDERED |
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583 | |
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584 | CALLING SEQUENCE: |
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585 | .. code-block:: c |
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586 | |
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587 | RTEMS_LINKER_RWSET_ITEM_ORDERED( set, type, item, order ); |
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588 | |
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589 | DESCRIPTION: |
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590 | This macro generates a definition of an ordered item contained in the |
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591 | read-write linker set identified by ``set``. The ``set`` parameter itself |
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592 | must be a valid C designator on which no macro expansion is performed. It |
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593 | uniquely identifies the linker set. The ``type`` parameter defines the type |
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594 | of the linker set items. The type must be the same for all macro |
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595 | invocations of a particular linker set. The ``item`` parameter itself must |
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596 | be a valid C designator on which no macro expansion is performed. It |
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597 | uniquely identifies an item in the linker set. The ``order`` parameter must |
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598 | be a valid linker input section name part on which macro expansion is |
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599 | performed. The items are lexicographically ordered according to the |
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600 | ``order`` parameter within a linker set. Ordered items are placed before |
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601 | unordered items in the linker set. |
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602 | |
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603 | NOTES: |
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604 | To be resilient to typos in the order parameter, it is recommended to use |
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605 | the following construct in macros defining items for a particular linker |
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606 | set (see enum in ``XYZ_ITEM()``). |
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607 | |
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608 | .. code-block:: c |
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609 | |
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610 | #include <rtems/linkersets.h> |
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611 | |
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612 | typedef struct { |
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613 | int foo; |
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614 | } xyz_item; |
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615 | |
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616 | /* The XYZ-order defines */ |
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617 | #define XYZ_ORDER_FIRST 0x00001000 |
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618 | #define XYZ_ORDER_AND_SO_ON 0x00002000 |
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619 | |
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620 | /* Defines an ordered XYZ-item */ |
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621 | #define XYZ_ITEM( item, order ) \ |
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622 | enum { xyz_##item = order - order }; \ |
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623 | RTEMS_LINKER_RWSET_ITEM_ORDERED( \ |
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624 | xyz, const xyz_item *, item, order \ |
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625 | ) = { &item } |
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626 | /* Example item */ |
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627 | static const xyz_item some_item = { 123 }; |
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628 | XYZ_ITEM( some_item, XYZ_ORDER_FIRST ); |
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