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/*
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* Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#ifndef ASM_MACROS_COMMON_S
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#define ASM_MACROS_COMMON_S
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/*
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* This macro is used to create a function label and place the
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* code into a separate text section based on the function name
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* to enable elimination of unused code during linking. It also adds
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* basic debug information to enable call stack printing most of the
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Add new alignment parameter to func assembler macro
Assembler programmers are used to being able to define functions with a
specific aligment with a pattern like this:
.align X
myfunction:
However, this pattern is subtly broken when instead of a direct label
like 'myfunction:', you use the 'func myfunction' macro that's standard
in Trusted Firmware. Since the func macro declares a new section for the
function, the .align directive written above it actually applies to the
*previous* section in the assembly file, and the function it was
supposed to apply to is linked with default alignment.
An extreme case can be seen in Rockchip's plat_helpers.S which contains
this code:
[...]
endfunc plat_crash_console_putc
.align 16
func platform_cpu_warmboot
[...]
This assembles into the following plat_helpers.o:
Sections:
Idx Name Size [...] Algn
9 .text.plat_crash_console_putc 00010000 [...] 2**16
10 .text.platform_cpu_warmboot 00000080 [...] 2**3
As can be seen, the *previous* function actually got the alignment
constraint, and it is also 64KB big even though it contains only two
instructions, because the .align directive at the end of its section
forces the assembler to insert a giant sled of NOPs. The function we
actually wanted to align has the default constraint. This code only
works at all because the linker just happens to put the two functions
right behind each other when linking the final image, and since the end
of plat_crash_console_putc is aligned the start of platform_cpu_warmboot
will also be. But it still wastes almost 64KB of image space
unnecessarily, and it will break under certain circumstances (e.g. if
the plat_crash_console_putc function becomes unused and its section gets
garbage-collected out).
There's no real way to fix this with the existing func macro. Code like
func myfunc
.align X
happens to do the right thing, but is still not really correct code
(because the function label is inserted before the .align directive, so
the assembler is technically allowed to insert padding at the beginning
of the function which would then get executed as instructions if the
function was called). Therefore, this patch adds a new parameter with a
default value to the func macro that allows overriding its alignment.
Also fix up all existing instances of this dangerous antipattern.
Change-Id: I5696a07e2fde896f21e0e83644c95b7b6ac79a10
Signed-off-by: Julius Werner <jwerner@chromium.org>
7 years ago
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* time. The optional _align parameter can be used to force a
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* non-standard alignment (indicated in powers of 2). The default is
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* _align=2 because both Aarch32 and Aarch64 instructions must be
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* word aligned. Do *not* try to use a raw .align directive. Since func
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* switches to a new section, this would not have the desired effect.
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*/
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.macro func _name, _align=2
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/*
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* Add Call Frame Information entry in the .debug_frame section for
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* debugger consumption. This enables callstack printing in debuggers.
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* This does not use any space in the final loaded binary, only in the
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* ELF file.
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* Note that a function manipulating the CFA pointer location (i.e. the
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* x29 frame pointer on AArch64) should declare it using the
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* appropriate .cfi* directives, or be prepared to have a degraded
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* debugging experience.
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*/
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.cfi_sections .debug_frame
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.section .text.asm.\_name, "ax"
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.type \_name, %function
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/*
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* .cfi_startproc and .cfi_endproc are needed to output entries in
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* .debug_frame
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*/
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.cfi_startproc
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.align \_align
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\_name:
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#if ENABLE_BTI
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/* When Branch Target Identification is enabled, insert "bti jc"
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* instruction to enable indirect calls and branches
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*/
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bti jc
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#endif
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.endm
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/*
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* This macro is used to mark the end of a function.
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*/
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.macro endfunc _name
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.cfi_endproc
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.size \_name, . - \_name
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.endm
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/*
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* Theses macros are used to create function labels for deprecated
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* APIs. If ERROR_DEPRECATED is non zero, the callers of these APIs
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* will fail to link and cause build failure.
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*/
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#if ERROR_DEPRECATED
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.macro func_deprecated _name
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func deprecated\_name
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.endm
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.macro endfunc_deprecated _name
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endfunc deprecated\_name
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.endm
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#else
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.macro func_deprecated _name
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func \_name
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.endm
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.macro endfunc_deprecated _name
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endfunc \_name
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.endm
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#endif
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/*
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* Helper assembler macro to count trailing zeros. The output is
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* populated in the `TZ_COUNT` symbol.
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*/
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.macro count_tz _value, _tz_count
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.if \_value
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count_tz "(\_value >> 1)", "(\_tz_count + 1)"
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.else
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.equ TZ_COUNT, (\_tz_count - 1)
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.endif
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.endm
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/*
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* This macro declares an array of 1 or more stacks, properly
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* aligned and in the requested section
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*/
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#define DEFAULT_STACK_ALIGN (1 << 6) /* In case the caller doesnt provide alignment */
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.macro declare_stack _name, _section, _size, _count, _align=DEFAULT_STACK_ALIGN
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count_tz \_align, 0
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.if (\_align - (1 << TZ_COUNT))
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.error "Incorrect stack alignment specified (Must be a power of 2)."
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.endif
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.if ((\_size & ((1 << TZ_COUNT) - 1)) <> 0)
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.error "Stack size not correctly aligned"
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.endif
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.section \_section, "aw", %nobits
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.align TZ_COUNT
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\_name:
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.space ((\_count) * (\_size)), 0
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.endm
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#endif /* ASM_MACROS_COMMON_S */
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