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diff --git a/doc/linker_lists.rst b/doc/linker_lists.rst new file mode 100644 index 0000000000..72f514e0ac --- /dev/null +++ b/doc/linker_lists.rst @@ -0,0 +1,100 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +Linker-Generated Arrays +======================= + +A linker list is constructed by grouping together linker input +sections, each containing one entry of the list. Each input section +contains a constant initialized variable which holds the entry's +content. Linker list input sections are constructed from the list +and entry names, plus a prefix which allows grouping all lists +together. Assuming _list and _entry are the list and entry names, +then the corresponding input section name is + +:: + + .u_boot_list_ + 2_ + @_list + _2_ + @_entry + +and the C variable name is + +:: + + _u_boot_list + _2_ + @_list + _2_ + @_entry + +This ensures uniqueness for both input section and C variable name. + +Note that the names differ only in the first character, "." for the +section and "_" for the variable, so that the linker cannot confuse +section and symbol names. From now on, both names will be referred +to as + +:: + + %u_boot_list_ + 2_ + @_list + _2_ + @_entry + +Entry variables need never be referred to directly. + +The naming scheme for input sections allows grouping all linker lists +into a single linker output section and grouping all entries for a +single list. + +Note the two '_2_' constant components in the names: their presence +allows putting a start and end symbols around a list, by mapping +these symbols to sections names with components "1" (before) and +"3" (after) instead of "2" (within). +Start and end symbols for a list can generally be defined as + +:: + + %u_boot_list_2_ + @_list + _1_... + %u_boot_list_2_ + @_list + _3_... + +Start and end symbols for the whole of the linker lists area can be +defined as + +:: + + %u_boot_list_1_... + %u_boot_list_3_... + +Here is an example of the sorted sections which result from a list +"array" made up of three entries : "first", "second" and "third", +iterated at least once. + +:: + + .u_boot_list_2_array_1 + .u_boot_list_2_array_2_first + .u_boot_list_2_array_2_second + .u_boot_list_2_array_2_third + .u_boot_list_2_array_3 + +If lists must be divided into sublists (e.g. for iterating only on +part of a list), one can simply give the list a name of the form +'outer_2_inner', where 'outer' is the global list name and 'inner' +is the sub-list name. Iterators for the whole list should use the +global list name ("outer"); iterators for only a sub-list should use +the full sub-list name ("outer_2_inner"). + +Here is an example of the sections generated from a global list +named "drivers", two sub-lists named "i2c" and "pci", and iterators +defined for the whole list and each sub-list: + +:: + + %u_boot_list_2_drivers_1 + %u_boot_list_2_drivers_2_i2c_1 + %u_boot_list_2_drivers_2_i2c_2_first + %u_boot_list_2_drivers_2_i2c_2_first + %u_boot_list_2_drivers_2_i2c_2_second + %u_boot_list_2_drivers_2_i2c_2_third + %u_boot_list_2_drivers_2_i2c_3 + %u_boot_list_2_drivers_2_pci_1 + %u_boot_list_2_drivers_2_pci_2_first + %u_boot_list_2_drivers_2_pci_2_second + %u_boot_list_2_drivers_2_pci_2_third + %u_boot_list_2_drivers_2_pci_3 + %u_boot_list_2_drivers_3 + +.. kernel-doc:: include/linker_lists.h + :internal: |