linker list

本文主要是介绍linker list，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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 <marex@denx.de>*/#ifndef __LINKER_LISTS_H__
#define __LINKER_LISTS_H__#include <linux/compiler.h>/** 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)