linker list

linker list是利用lds 描述符实现同类型数据连续排布的一种机制。
下面是uboot里面的应用说明

lds文件里面需要增加section描述：

	. = ALIGN(4);
	.u_boot_list : {
		KEEP(*(SORT(.u_boot_list*)));
	}

linker_list.h:

/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * include/linker_lists.h
 *
 * Implementation of linker-generated arrays
 *
 * Copyright (C) 2012 Marek Vasut 
 */

#ifndef __LINKER_LISTS_H__
#define __LINKER_LISTS_H__

#include 

/*
 * There is no use in including this from ASM files.
 * So just don't define anything when included from ASM.
 */

#if !defined(__ASSEMBLY__)

/**
 * llsym() - Access a linker-generated array entry
 * @_type:	Data type of the entry
 * @_name:	Name of the entry
 * @_list:	name of the list. Should contain only characters allowed
 *		in a C variable name!
 */
#define llsym(_type, _name, _list) \
		((_type *)&_u_boot_list_2_##_list##_2_##_name)

/**
 * ll_entry_declare() - Declare linker-generated array entry
 * @_type:	Data type of the entry
 * @_name:	Name of the entry
 * @_list:	name of the list. Should contain only characters allowed
 *		in a C variable name!
 *
 * This macro declares a variable that is placed into a linker-generated
 * array. This is a basic building block for more advanced use of linker-
 * generated arrays. The user is expected to build their own macro wrapper
 * around this one.
 *
 * A variable declared using this macro must be compile-time initialized.
 *
 * Special precaution must be made when using this macro:
 *
 * 1) The _type must not contain the "static" keyword, otherwise the
 *    entry is generated and can be iterated but is listed in the map
 *    file and cannot be retrieved by name.
 *
 * 2) In case a section is declared that contains some array elements AND
 *    a subsection of this section is declared and contains some elements,
 *    it is imperative that the elements are of the same type.
 *
 * 3) In case an outer section is declared that contains some array elements
 *    AND an inner subsection of this section is declared and contains some
 *    elements, then when traversing the outer section, even the elements of
 *    the inner sections are present in the array.
 *
 * Example:
 *
 * ::
 *
 *   ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
 *           .x = 3,
 *           .y = 4,
 *   };
 */
#define ll_entry_declare(_type, _name, _list)				\
	_type _u_boot_list_2_##_list##_2_##_name __aligned(4)		\
			__attribute__((unused,				\
			section(".u_boot_list_2_"#_list"_2_"#_name)))

/**
 * ll_entry_declare_list() - Declare a list of link-generated array entries
 * @_type:	Data type of each entry
 * @_name:	Name of the entry
 * @_list:	name of the list. Should contain only characters allowed
 *		in a C variable name!
 *
 * This is like ll_entry_declare() but creates multiple entries. It should
 * be assigned to an array.
 *
 * ::
 *
 *   ll_entry_declare_list(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
 *        { .x = 3, .y = 4 },
 *        { .x = 8, .y = 2 },
 *        { .x = 1, .y = 7 }
 *   };
 */
#define ll_entry_declare_list(_type, _name, _list)			\
	_type _u_boot_list_2_##_list##_2_##_name[] __aligned(4)		\
			__attribute__((unused,				\
			section(".u_boot_list_2_"#_list"_2_"#_name)))

/*
 * We need a 0-byte-size type for iterator symbols, and the compiler
 * does not allow defining objects of C type 'void'. Using an empty
 * struct is allowed by the compiler, but causes gcc versions 4.4 and
 * below to complain about aliasing. Therefore we use the next best
 * thing: zero-sized arrays, which are both 0-byte-size and exempt from
 * aliasing warnings.
 */

/**
 * ll_entry_start() - Point to first entry of linker-generated array
 * @_type:	Data type of the entry
 * @_list:	Name of the list in which this entry is placed
 *
 * This function returns ``(_type *)`` pointer to the very first entry of a
 * linker-generated array placed into subsection of .u_boot_list section
 * specified by _list argument.
 *
 * Since this macro defines an array start symbol, its leftmost index
 * must be 2 and its rightmost index must be 1.
 *
 * Example:
 *
 * ::
 *
 *   struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
 */
#define ll_entry_start(_type, _list)					\
({									\
	static char start[0] __aligned(4) __attribute__((unused,	\
		section(".u_boot_list_2_"#_list"_1")));			\
	(_type *)&start;						\
})

/**
 * ll_entry_end() - Point after last entry of linker-generated array
 * @_type:	Data type of the entry
 * @_list:	Name of the list in which this entry is placed
 *		(with underscores instead of dots)
 *
 * This function returns ``(_type *)`` pointer after the very last entry of
 * a linker-generated array placed into subsection of .u_boot_list
 * section specified by _list argument.
 *
 * Since this macro defines an array end symbol, its leftmost index
 * must be 2 and its rightmost index must be 3.
 *
 * Example:
 *
 * ::
 *
 *   struct my_sub_cmd *msc = ll_entry_end(struct my_sub_cmd, cmd_sub);
 */
#define ll_entry_end(_type, _list)					\
({									\
	static char end[0] __aligned(4) __attribute__((unused,		\
		section(".u_boot_list_2_"#_list"_3")));			\
	(_type *)&end;							\
})
/**
 * ll_entry_count() - Return the number of elements in linker-generated array
 * @_type:	Data type of the entry
 * @_list:	Name of the list of which the number of elements is computed
 *
 * This function returns the number of elements of a linker-generated array
 * placed into subsection of .u_boot_list section specified by _list
 * argument. The result is of an unsigned int type.
 *
 * Example:
 *
 * ::
 *
 *   int i;
 *   const unsigned int count = ll_entry_count(struct my_sub_cmd, cmd_sub);
 *   struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
 *   for (i = 0; i < count; i++, msc++)
 *           printf("Entry %i, x=%i y=%i\n", i, msc->x, msc->y);
 */
#define ll_entry_count(_type, _list)					\
	({								\
		_type *start = ll_entry_start(_type, _list);		\
		_type *end = ll_entry_end(_type, _list);		\
		unsigned int _ll_result = end - start;			\
		_ll_result;						\
	})

/**
 * ll_entry_get() - Retrieve entry from linker-generated array by name
 * @_type:	Data type of the entry
 * @_name:	Name of the entry
 * @_list:	Name of the list in which this entry is placed
 *
 * This function returns a pointer to a particular entry in linker-generated
 * array identified by the subsection of u_boot_list where the entry resides
 * and it's name.
 *
 * Example:
 *
 * ::
 *
 *   ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
 *           .x = 3,
 *           .y = 4,
 *   };
 *   ...
 *   struct my_sub_cmd *c = ll_entry_get(struct my_sub_cmd, my_sub_cmd, cmd_sub);
 */
#define ll_entry_get(_type, _name, _list)				\
	({								\
		extern _type _u_boot_list_2_##_list##_2_##_name;	\
		_type *_ll_result =					\
			&_u_boot_list_2_##_list##_2_##_name;		\
		_ll_result;						\
	})

/**
 * ll_start() - Point to first entry of first linker-generated array
 * @_type:	Data type of the entry
 *
 * This function returns ``(_type *)`` pointer to the very first entry of
 * the very first linker-generated array.
 *
 * Since this macro defines the start of the linker-generated arrays,
 * its leftmost index must be 1.
 *
 * Example:
 *
 * ::
 *
 *   struct my_sub_cmd *msc = ll_start(struct my_sub_cmd);
 */
#define ll_start(_type)							\
({									\
	static char start[0] __aligned(4) __attribute__((unused,	\
		section(".u_boot_list_1")));				\
	(_type *)&start;						\
})

/**
 * ll_end() - Point after last entry of last linker-generated array
 * @_type:	Data type of the entry
 *
 * This function returns ``(_type *)`` pointer after the very last entry of
 * the very last linker-generated array.
 *
 * Since this macro defines the end of the linker-generated arrays,
 * its leftmost index must be 3.
 *
 * Example:
 *
 * ::
 *
 *   struct my_sub_cmd *msc = ll_end(struct my_sub_cmd);
 */
#define ll_end(_type)							\
({									\
	static char end[0] __aligned(4) __attribute__((unused,		\
		section(".u_boot_list_3")));				\
	(_type *)&end;							\
})

#endif /* __ASSEMBLY__ */

#endif	/* __LINKER_LISTS_H__ */

ll_entry_declare_list 和ll_entry_declare差别是前者是数组声明，一次可以声明多个条目，后者只声明（定义）一个条目。

ll_entry_start(_type, _list) 获取该类型列表首个条目地址

ll_entry_get(_type, _name, _list) 根据名字 返回条目地址

ll_entry_count(_type, _list) 返回该类型条目数

使用实例

参考driver的定义：

struct driver {
	char *name;
	enum uclass_id id;
	const struct udevice_id *of_match;
	int (*bind)(struct udevice *dev);
	int (*probe)(struct udevice *dev);
	int (*remove)(struct udevice *dev);
	int (*unbind)(struct udevice *dev);
	int (*ofdata_to_platdata)(struct udevice *dev);
	int (*child_post_bind)(struct udevice *dev);
	int (*child_pre_probe)(struct udevice *dev);
	int (*child_post_remove)(struct udevice *dev);
	int priv_auto_alloc_size;
	int platdata_auto_alloc_size;
	int per_child_auto_alloc_size;
	int per_child_platdata_auto_alloc_size;
	const void *ops;	/* driver-specific operations */
	uint32_t flags;
};

/* Declare a new U-Boot driver */
#define U_BOOT_DRIVER(__name)						\
	ll_entry_declare(struct driver, __name, driver)

usb hub driver

U_BOOT_DRIVER(usb_generic_hub) = {
.name = “usb_hub”,
.id = UCLASS_USB_HUB,
.of_match = usb_hub_ids,
.flags = DM_FLAG_ALLOC_PRIV_DMA,
};