forked from Minki/linux
6c94f27ac8
Instead of using absolute addresses for both the exception location and the fixup, use offsets relative to the exception table entry values. Not only does this cut the size of the exception table in half, it is also a prerequisite for KASLR, since absolute exception table entries are subject to dynamic relocation, which is incompatible with the sorting of the exception table that occurs at build time. This patch also introduces the _ASM_EXTABLE preprocessor macro (which exists on x86 as well) and its _asm_extable assembly counterpart, as shorthands to emit exception table entries. Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
215 lines
5.7 KiB
C
215 lines
5.7 KiB
C
#ifndef __ASM_ALTERNATIVE_H
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#define __ASM_ALTERNATIVE_H
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#include <asm/cpufeature.h>
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#ifndef __ASSEMBLY__
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#include <linux/init.h>
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#include <linux/kconfig.h>
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#include <linux/types.h>
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#include <linux/stddef.h>
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#include <linux/stringify.h>
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struct alt_instr {
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s32 orig_offset; /* offset to original instruction */
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s32 alt_offset; /* offset to replacement instruction */
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u16 cpufeature; /* cpufeature bit set for replacement */
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u8 orig_len; /* size of original instruction(s) */
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u8 alt_len; /* size of new instruction(s), <= orig_len */
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};
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void __init apply_alternatives_all(void);
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void apply_alternatives(void *start, size_t length);
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#define ALTINSTR_ENTRY(feature) \
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" .word 661b - .\n" /* label */ \
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" .word 663f - .\n" /* new instruction */ \
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" .hword " __stringify(feature) "\n" /* feature bit */ \
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" .byte 662b-661b\n" /* source len */ \
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" .byte 664f-663f\n" /* replacement len */
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/*
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* alternative assembly primitive:
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*
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* If any of these .org directive fail, it means that insn1 and insn2
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* don't have the same length. This used to be written as
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*
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* .if ((664b-663b) != (662b-661b))
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* .error "Alternatives instruction length mismatch"
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* .endif
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*
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* but most assemblers die if insn1 or insn2 have a .inst. This should
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* be fixed in a binutils release posterior to 2.25.51.0.2 (anything
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* containing commit 4e4d08cf7399b606 or c1baaddf8861).
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*/
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#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled) \
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".if "__stringify(cfg_enabled)" == 1\n" \
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"661:\n\t" \
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oldinstr "\n" \
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"662:\n" \
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".pushsection .altinstructions,\"a\"\n" \
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ALTINSTR_ENTRY(feature) \
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".popsection\n" \
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".pushsection .altinstr_replacement, \"a\"\n" \
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"663:\n\t" \
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newinstr "\n" \
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"664:\n\t" \
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".popsection\n\t" \
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".org . - (664b-663b) + (662b-661b)\n\t" \
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".org . - (662b-661b) + (664b-663b)\n" \
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".endif\n"
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#define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...) \
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__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))
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#else
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#include <asm/assembler.h>
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.macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
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.word \orig_offset - .
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.word \alt_offset - .
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.hword \feature
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.byte \orig_len
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.byte \alt_len
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.endm
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.macro alternative_insn insn1, insn2, cap, enable = 1
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.if \enable
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661: \insn1
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662: .pushsection .altinstructions, "a"
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altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
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.popsection
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.pushsection .altinstr_replacement, "ax"
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663: \insn2
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664: .popsection
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.org . - (664b-663b) + (662b-661b)
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.org . - (662b-661b) + (664b-663b)
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.endif
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.endm
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/*
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* Begin an alternative code sequence.
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*
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* The code that follows this macro will be assembled and linked as
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* normal. There are no restrictions on this code.
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*/
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.macro alternative_if_not cap, enable = 1
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.if \enable
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.pushsection .altinstructions, "a"
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altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
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.popsection
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661:
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.endif
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.endm
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/*
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* Provide the alternative code sequence.
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*
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* The code that follows this macro is assembled into a special
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* section to be used for dynamic patching. Code that follows this
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* macro must:
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*
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* 1. Be exactly the same length (in bytes) as the default code
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* sequence.
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*
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* 2. Not contain a branch target that is used outside of the
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* alternative sequence it is defined in (branches into an
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* alternative sequence are not fixed up).
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*/
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.macro alternative_else, enable = 1
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.if \enable
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662: .pushsection .altinstr_replacement, "ax"
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663:
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.endif
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.endm
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/*
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* Complete an alternative code sequence.
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*/
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.macro alternative_endif, enable = 1
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.if \enable
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664: .popsection
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.org . - (664b-663b) + (662b-661b)
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.org . - (662b-661b) + (664b-663b)
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.endif
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.endm
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#define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...) \
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alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
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/*
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* Generate the assembly for UAO alternatives with exception table entries.
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* This is complicated as there is no post-increment or pair versions of the
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* unprivileged instructions, and USER() only works for single instructions.
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*/
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#ifdef CONFIG_ARM64_UAO
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.macro uao_ldp l, reg1, reg2, addr, post_inc
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alternative_if_not ARM64_HAS_UAO
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8888: ldp \reg1, \reg2, [\addr], \post_inc;
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8889: nop;
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nop;
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alternative_else
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ldtr \reg1, [\addr];
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ldtr \reg2, [\addr, #8];
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add \addr, \addr, \post_inc;
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alternative_endif
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_asm_extable 8888b,\l;
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_asm_extable 8889b,\l;
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.endm
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.macro uao_stp l, reg1, reg2, addr, post_inc
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alternative_if_not ARM64_HAS_UAO
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8888: stp \reg1, \reg2, [\addr], \post_inc;
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8889: nop;
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nop;
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alternative_else
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sttr \reg1, [\addr];
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sttr \reg2, [\addr, #8];
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add \addr, \addr, \post_inc;
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alternative_endif
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_asm_extable 8888b,\l;
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_asm_extable 8889b,\l;
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.endm
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.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
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alternative_if_not ARM64_HAS_UAO
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8888: \inst \reg, [\addr], \post_inc;
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nop;
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alternative_else
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\alt_inst \reg, [\addr];
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add \addr, \addr, \post_inc;
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alternative_endif
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_asm_extable 8888b,\l;
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.endm
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#else
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.macro uao_ldp l, reg1, reg2, addr, post_inc
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USER(\l, ldp \reg1, \reg2, [\addr], \post_inc)
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.endm
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.macro uao_stp l, reg1, reg2, addr, post_inc
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USER(\l, stp \reg1, \reg2, [\addr], \post_inc)
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.endm
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.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
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USER(\l, \inst \reg, [\addr], \post_inc)
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.endm
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#endif
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#endif /* __ASSEMBLY__ */
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/*
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* Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
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*
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* Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
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* N.B. If CONFIG_FOO is specified, but not selected, the whole block
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* will be omitted, including oldinstr.
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*/
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#define ALTERNATIVE(oldinstr, newinstr, ...) \
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_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
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#endif /* __ASM_ALTERNATIVE_H */
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