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0b2fa98aa5
The linker script uses alphabetic sorting to group the different linker
lists together. Each group has its own struct and potentially its own
alignment. But when the linker packs the structs together it cannot ensure
that a linker list starts on the expected alignment boundary.
For example, if the first list has a struct size of 8 and we place 3 of
them in the image, that means that the next struct will start at offset
0x18 from the start of the linker_list section. If the next struct has
a size of 16 then it will start at an 8-byte aligned offset, but not a
16-byte aligned offset.
With sandbox on x86_64, a reference to a linker list item using
ll_entry_get() can force alignment of that particular linker_list item,
if it is in the same file as the linker_list item is declared.
Consider this example, where struct driver is 0x80 bytes:
ll_entry_declare(struct driver, fred, driver)
...
void *p = ll_entry_get(struct driver, fred, driver)
If these two lines of code are in the same file, then the entry is forced
to be aligned at the 'struct driver' alignment, which is 16 bytes. If the
second line of code is in a different file, then no action is taken, since
the compiler cannot update the alignment of the linker_list item.
In the first case, an 8-byte 'fill' region is added:
.u_boot_list_2_driver_2_testbus_drv
0x0000000000270018 0x80 test/built-in.o
0x0000000000270018 _u_boot_list_2_driver_2_testbus_drv
.u_boot_list_2_driver_2_testfdt1_drv
0x0000000000270098 0x80 test/built-in.o
0x0000000000270098 _u_boot_list_2_driver_2_testfdt1_drv
*fill* 0x0000000000270118 0x8
.u_boot_list_2_driver_2_testfdt_drv
0x0000000000270120 0x80 test/built-in.o
0x0000000000270120 _u_boot_list_2_driver_2_testfdt_drv
.u_boot_list_2_driver_2_testprobe_drv
0x00000000002701a0 0x80 test/built-in.o
0x00000000002701a0 _u_boot_list_2_driver_2_testprobe_drv
With this, the linker_list no-longer works since items after testfdt1_drv
are not at the expected address.
Ideally we would have a way to tell gcc not to align structs in this way.
It is not clear how we could do this, and in any case it would require us
to adjust every struct used by the linker_list feature.
One possible fix is to force each separate linker_list to start on the
largest possible boundary that can be required by the compiler. However
that does not seem to work on x86_64, which uses 16-byte alignment in this
case but needs 32-byte alignment.
So add a Kconfig option to handle this. Set the default value to 4 so
as to avoid changing platforms that don't need it.
Update the ll_entry_start() accordingly.
Signed-off-by: Simon Glass <sjg@chromium.org>
262 lines
7.8 KiB
C
262 lines
7.8 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 *)&start; \
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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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* 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(4) __attribute__((unused, \
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section(".u_boot_list_2_"#_list"_3"))); \
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(_type *)&end; \
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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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* 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_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 *)&start; \
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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 *)&end; \
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})
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#endif /* __ASSEMBLY__ */
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#endif /* __LINKER_LISTS_H__ */
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