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Improve support for linker lists in data structures

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A limitation of most linker_list macros is that they cannot easily be
used in data structures. This is because they include code inside their
expressions.

Provide a way to support this, with new ll_start_decl() and
ll_end_decl() macros.

Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass 2025-01-20 14:25:27 -07:00 • committed by Tom Rini
parent 94b5284398
commit f0781acc37
1 changed files with 57 additions and 0 deletions
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57
include/linker_lists.h
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@ -186,6 +186,63 @@
_ll_result; \
})
/**
* Declares a symbol that points to the start/end of the list.
*
* @_sym: Arbitrary name for the symbol (to use later in the file)
* @_type: Data type of the entry
* @_list: Name of the list in which this entry is placed
*
* The name of the (new) symbol is arbitrary and can be anything that is not
* already declared in the file where it appears. It is provided in _sym and
* can then be used (later in the same file) within a data structure.
* The _type and _list arguments must match those passed to ll_entry_start/end()
*
* Example:
*
* Here we want to record the start of each sub-command in a list. We have two
* sub-commands, 'bob' and 'mary'.
*
* In bob.c::
*
* ll_entry_declare(struct my_sub_cmd, bob_cmd, cmd_sub) = {...};
*
* In mary.c::
*
* ll_entry_declare(struct my_sub_cmd, mary_cmd, cmd_sub) = {...};
*
* In a different file where we want a list the start of all sub-commands.
* It is not possible to use ll_entry_start() in a data structure, due to its
* use of code inside expressions - ({ ... }) - so this fails to compile:
*
* In sub_cmds.c::
*
* struct cmd_sub *my_list[] = {
* ll_entry_start(cmd_sub, bob),
* ll_entry_start(cmd_sub, bob),
* };
*
* Instead, we can use::
*
* ll_start_decl(bob, struct my_sub_cmd, cmd_sub);
* ll_start_decl(mary, struct my_sub_cmd, cmd_sub);
*
* struct cmd_sub *my_list[] = {
* bob,
* mary,
* };
*
* So 'bob' is declared as symbol, a struct my_list * which points to the
* start of the bob sub-commands. It is then used in my_list[]
*/
#define ll_start_decl(_sym, _type, _list) \
static _type _sym[0] __aligned(CONFIG_LINKER_LIST_ALIGN) \
__maybe_unused __section("__u_boot_list_2_" #_list "_1")
#define ll_end_decl(_sym, _type, _list) \
static _type _sym[0] __aligned(CONFIG_LINKER_LIST_ALIGN) \
__maybe_unused __section("__u_boot_list_2_" #_list "_3")
/**
* ll_entry_get() - Retrieve entry from linker-generated array by name
* @_type: Data type of the entry