9ab3308d64
Change the alignment of end markers in ll_entry_end() and ll_end_decl()
from __aligned(4) and __aligned(CONFIG_LINKER_LIST_ALIGN) respectively
to __aligned(1).
The linker places zero-size end markers at aligned boundaries based on
what follows them. When the next list's start marker has a high alignment
requirement (e.g., 32 bytes), padding gets inserted before the end marker.
This causes the byte span (end - start) to not be an exact multiple of
the struct size.
The compiler optimizes pointer subtraction (end - start) using magic-number
multiplication for division. This optimization only produces correct results
when the byte span is an exact multiple of the struct size. With padding,
the result is garbage (e.g., -858993444 instead of 15).
By using __aligned(1), the end marker is placed immediately after the last
entry with no padding, ensuring (end - start) equals exactly n * sizeof
where n is the number of entries. This makes ll_entry_count() and direct
pointer arithmetic work correctly.
Fixes: 0b2fa98aa5 ("linker_lists: Fix alignment issue")
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
362 lines
11 KiB
C
362 lines
11 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* include/linker_lists.h
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*
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* Implementation of linker-generated arrays
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*
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* Copyright (C) 2012 Marek Vasut <marex@denx.de>
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*/
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#ifndef __LINKER_LISTS_H__
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#define __LINKER_LISTS_H__
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#include <linux/compiler.h>
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/*
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* There is no use in including this from ASM files.
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* So just don't define anything when included from ASM.
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*/
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#if !defined(__ASSEMBLY__)
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/**
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* llsym() - Access a linker-generated array entry
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* @_type: Data type of the entry
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* @_name: Name of the entry
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* @_list: name of the list. Should contain only characters allowed
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* in a C variable name!
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*/
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#define llsym(_type, _name, _list) \
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((_type *)&_u_boot_list_2_##_list##_2_##_name)
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/**
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* ll_entry_declare() - Declare linker-generated array entry
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* @_type: Data type of the entry
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* @_name: Name of the entry
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* @_list: name of the list. Should contain only characters allowed
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* in a C variable name!
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*
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* This macro declares a variable that is placed into a linker-generated
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* array. This is a basic building block for more advanced use of linker-
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* generated arrays. The user is expected to build their own macro wrapper
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* around this one.
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*
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* A variable declared using this macro must be compile-time initialized.
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*
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* Special precaution must be made when using this macro:
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*
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* 1) The _type must not contain the "static" keyword, otherwise the
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* entry is generated and can be iterated but is listed in the map
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* file and cannot be retrieved by name.
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*
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* 2) In case a section is declared that contains some array elements AND
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* a subsection of this section is declared and contains some elements,
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* it is imperative that the elements are of the same type.
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*
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* 3) In case an outer section is declared that contains some array elements
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* AND an inner subsection of this section is declared and contains some
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* elements, then when traversing the outer section, even the elements of
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* the inner sections are present in the array.
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*
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* Example:
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*
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* ::
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*
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* ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
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* .x = 3,
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* .y = 4,
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* };
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*/
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#define ll_entry_declare(_type, _name, _list) \
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_type _u_boot_list_2_##_list##_2_##_name __aligned(4) \
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__attribute__((unused)) \
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__section("__u_boot_list_2_"#_list"_2_"#_name)
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/**
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* ll_entry_declare_list() - Declare a list of link-generated array entries
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* @_type: Data type of each entry
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* @_name: Name of the entry
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* @_list: name of the list. Should contain only characters allowed
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* in a C variable name!
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*
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* This is like ll_entry_declare() but creates multiple entries. It should
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* be assigned to an array.
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*
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* ::
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*
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* ll_entry_declare_list(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
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* { .x = 3, .y = 4 },
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* { .x = 8, .y = 2 },
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* { .x = 1, .y = 7 }
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* };
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*/
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#define ll_entry_declare_list(_type, _name, _list) \
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_type _u_boot_list_2_##_list##_2_##_name[] __aligned(4) \
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__attribute__((unused)) \
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__section("__u_boot_list_2_"#_list"_2_"#_name)
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/*
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* We need a 0-byte-size type for iterator symbols, and the compiler
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* does not allow defining objects of C type 'void'. Using an empty
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* struct is allowed by the compiler, but causes gcc versions 4.4 and
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* below to complain about aliasing. Therefore we use the next best
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* thing: zero-sized arrays, which are both 0-byte-size and exempt from
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* aliasing warnings.
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*/
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/**
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* ll_entry_start() - Point to first entry of linker-generated array
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* @_type: Data type of the entry
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* @_list: Name of the list in which this entry is placed
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*
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* This function returns ``(_type *)`` pointer to the very first entry of a
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* linker-generated array placed into subsection of __u_boot_list section
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* specified by _list argument.
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*
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* Since this macro defines an array start symbol, its leftmost index
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* must be 2 and its rightmost index must be 1.
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*
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* Example:
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*
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* ::
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*
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* struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
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*/
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#define ll_entry_start(_type, _list) \
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({ \
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static char start[0] __aligned(CONFIG_LINKER_LIST_ALIGN) \
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__attribute__((unused)) \
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__section("__u_boot_list_2_"#_list"_1"); \
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_type * tmp = (_type *)&start; \
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asm("":"+r"(tmp)); \
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tmp; \
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})
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/**
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* ll_entry_end() - Point after last entry of linker-generated array
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* @_type: Data type of the entry
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* @_list: Name of the list in which this entry is placed
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* (with underscores instead of dots)
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*
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* This function returns ``(_type *)`` pointer after the very last entry of
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* a linker-generated array placed into subsection of __u_boot_list
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* section specified by _list argument.
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*
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* Since this macro defines an array end symbol, its leftmost index
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* must be 2 and its rightmost index must be 3.
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*
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* The end symbol uses __aligned(1) to ensure it is placed immediately after
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* the last entry without any padding. This is critical for ll_entry_count()
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* to work correctly.
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*
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* If the end marker had a higher alignment (e.g., 4 or 32 bytes), the linker
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* might insert padding between the last entry and the end marker to satisfy
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* alignment requirements of the following section. This would cause pointer
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* subtraction (end - start) to produce incorrect results because the compiler
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* optimizes pointer division using magic-number multiplication, which only
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* works correctly when the byte span is an exact multiple of the struct size.
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*
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* With __aligned(1), the end marker is placed at exactly (start + n * sizeof)
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* where n is the number of entries, ensuring correct pointer arithmetic.
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*
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* Example:
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*
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* ::
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*
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* struct my_sub_cmd *msc = ll_entry_end(struct my_sub_cmd, cmd_sub);
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*/
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#define ll_entry_end(_type, _list) \
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({ \
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static char end[0] __aligned(1) __attribute__((unused)) \
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__section("__u_boot_list_2_"#_list"_3"); \
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_type * tmp = (_type *)&end; \
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asm("":"+r"(tmp)); \
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tmp; \
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})
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/**
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* ll_entry_count() - Return the number of elements in linker-generated array
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* @_type: Data type of the entry
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* @_list: Name of the list of which the number of elements is computed
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*
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* This function returns the number of elements of a linker-generated array
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* placed into subsection of __u_boot_list section specified by _list
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* argument. The result is of an unsigned int type.
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*
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* Example:
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*
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* ::
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*
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* int i;
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* const unsigned int count = ll_entry_count(struct my_sub_cmd, cmd_sub);
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* struct my_sub_cmd *msc = ll_entry_start(struct my_sub_cmd, cmd_sub);
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* for (i = 0; i < count; i++, msc++)
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* printf("Entry %i, x=%i y=%i\n", i, msc->x, msc->y);
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*/
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#define ll_entry_count(_type, _list) \
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({ \
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_type *start = ll_entry_start(_type, _list); \
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_type *end = ll_entry_end(_type, _list); \
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unsigned int _ll_result = end - start; \
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_ll_result; \
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})
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/**
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* Declares a symbol that points to the start/end of the list.
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*
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* @_sym: Arbitrary name for the symbol (to use later in the file)
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* @_type: Data type of the entry
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* @_list: Name of the list in which this entry is placed
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*
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* The name of the (new) symbol is arbitrary and can be anything that is not
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* already declared in the file where it appears. It is provided in _sym and
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* can then be used (later in the same file) within a data structure.
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* The _type and _list arguments must match those passed to ll_entry_start/end()
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*
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* Example:
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*
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* Here we want to record the start of each sub-command in a list. We have two
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* sub-commands, 'bob' and 'mary'.
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*
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* In bob.c::
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*
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* ll_entry_declare(struct my_sub_cmd, bob_cmd, cmd_sub) = {...};
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*
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* In mary.c::
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*
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* ll_entry_declare(struct my_sub_cmd, mary_cmd, cmd_sub) = {...};
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*
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* In a different file where we want a list the start of all sub-commands.
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* It is not possible to use ll_entry_start() in a data structure, due to its
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* use of code inside expressions - ({ ... }) - so this fails to compile:
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*
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* In sub_cmds.c::
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*
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* struct cmd_sub *my_list[] = {
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* ll_entry_start(cmd_sub, bob),
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* ll_entry_start(cmd_sub, bob),
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* };
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*
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* Instead, we can use::
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*
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* ll_start_decl(bob, struct my_sub_cmd, cmd_sub);
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* ll_start_decl(mary, struct my_sub_cmd, cmd_sub);
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*
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* struct cmd_sub *my_list[] = {
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* bob,
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* mary,
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* };
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*
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* So 'bob' is declared as symbol, a struct my_list * which points to the
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* start of the bob sub-commands. It is then used in my_list[]
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*/
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#define ll_start_decl(_sym, _type, _list) \
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static _type _sym[0] __aligned(CONFIG_LINKER_LIST_ALIGN) \
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__maybe_unused __section("__u_boot_list_2_" #_list "_1")
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/*
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* ll_end_decl uses __aligned(1) to avoid padding before the end marker.
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* See the comment for ll_entry_end() for a full explanation.
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*/
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#define ll_end_decl(_sym, _type, _list) \
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static _type _sym[0] __aligned(1) \
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__maybe_unused __section("__u_boot_list_2_" #_list "_3")
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/**
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* ll_entry_get() - Retrieve entry from linker-generated array by name
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* @_type: Data type of the entry
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* @_name: Name of the entry
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* @_list: Name of the list in which this entry is placed
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*
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* This function returns a pointer to a particular entry in linker-generated
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* array identified by the subsection of u_boot_list where the entry resides
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* and it's name.
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*
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* Example:
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*
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* ::
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*
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* ll_entry_declare(struct my_sub_cmd, my_sub_cmd, cmd_sub) = {
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* .x = 3,
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* .y = 4,
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* };
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* ...
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* struct my_sub_cmd *c = ll_entry_get(struct my_sub_cmd, my_sub_cmd, cmd_sub);
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*/
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#define ll_entry_get(_type, _name, _list) \
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({ \
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extern _type _u_boot_list_2_##_list##_2_##_name; \
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_type *_ll_result = \
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&_u_boot_list_2_##_list##_2_##_name; \
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_ll_result; \
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})
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/**
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* ll_entry_ref() - Get a reference to a linker-generated array entry
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*
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* Once an extern ll_entry_declare() has been used to declare the reference,
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* this macro allows the entry to be accessed.
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*
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* This is like ll_entry_get(), but without the extra code, so it is suitable
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* for putting into data structures.
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*
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* @_type: C type of the list entry, e.g. 'struct foo'
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* @_name: name of the entry
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* @_list: name of the list
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*/
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#define ll_entry_ref(_type, _name, _list) \
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((_type *)&_u_boot_list_2_##_list##_2_##_name)
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/**
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* ll_start() - Point to first entry of first linker-generated array
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* @_type: Data type of the entry
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*
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* This function returns ``(_type *)`` pointer to the very first entry of
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* the very first linker-generated array.
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*
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* Since this macro defines the start of the linker-generated arrays,
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* its leftmost index must be 1.
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*
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* Example:
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*
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* ::
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*
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* struct my_sub_cmd *msc = ll_start(struct my_sub_cmd);
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*/
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#define ll_start(_type) \
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({ \
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static char start[0] __aligned(4) __attribute__((unused)) \
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__section("__u_boot_list_1"); \
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_type * tmp = (_type *)&start; \
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asm("":"+r"(tmp)); \
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tmp; \
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})
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/**
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* ll_end() - Point after last entry of last linker-generated array
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* @_type: Data type of the entry
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*
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* This function returns ``(_type *)`` pointer after the very last entry of
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* the very last linker-generated array.
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*
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* Since this macro defines the end of the linker-generated arrays,
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* its leftmost index must be 3.
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*
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* Example:
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*
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* ::
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*
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* struct my_sub_cmd *msc = ll_end(struct my_sub_cmd);
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*/
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#define ll_end(_type) \
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({ \
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static char end[0] __aligned(4) __attribute__((unused)) \
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__section("__u_boot_list_3"); \
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_type * tmp = (_type *)&end; \
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asm("":"+r"(tmp)); \
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tmp; \
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})
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#endif /* __ASSEMBLY__ */
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#endif /* __LINKER_LISTS_H__ */
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