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dea5e2a4c5
We've so far relied on a patching infrastructure that only gave us
a single alternative, without any way to provide a range of potential
replacement instructions. For a single feature, this is an all or
nothing thing.
It would be interesting to have a more flexible grained way of patching
the kernel though, where we could dynamically tune the code that gets
injected.
In order to achive this, let's introduce a new form of dynamic patching,
assiciating a callback to a patching site. This callback gets source and
target locations of the patching request, as well as the number of
instructions to be patched.
Dynamic patching is declared with the new ALTERNATIVE_CB and alternative_cb
directives:
asm volatile(ALTERNATIVE_CB("mov %0, #0\n", callback)
: "r" (v));
or
alternative_cb callback
mov x0, #0
alternative_cb_end
where callback is the C function computing the alternative.
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
284 lines
7.4 KiB
C
284 lines
7.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_ALTERNATIVE_H
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#define __ASM_ALTERNATIVE_H
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#include <asm/cpucaps.h>
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#include <asm/insn.h>
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#define ARM64_CB_PATCH ARM64_NCAPS
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#ifndef __ASSEMBLY__
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#include <linux/init.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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extern int alternatives_applied;
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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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typedef void (*alternative_cb_t)(struct alt_instr *alt,
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__le32 *origptr, __le32 *updptr, int nr_inst);
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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,cb) \
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" .word 661b - .\n" /* label */ \
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" .if " __stringify(cb) " == 0\n" \
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" .word 663f - .\n" /* new instruction */ \
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" .else\n" \
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" .word " __stringify(cb) "- .\n" /* callback */ \
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" .endif\n" \
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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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* Alternatives with callbacks do not generate replacement instructions.
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*/
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#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled, cb) \
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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,cb) \
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".popsection\n" \
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" .if " __stringify(cb) " == 0\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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".else\n\t" \
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"663:\n\t" \
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"664:\n\t" \
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".endif\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), 0)
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#define ALTERNATIVE_CB(oldinstr, cb) \
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__ALTERNATIVE_CFG(oldinstr, "NOT_AN_INSTRUCTION", ARM64_CB_PATCH, 1, cb)
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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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* Alternative sequences
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*
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* The code for the case where the capability is not present will be
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* assembled and linked as normal. There are no restrictions on this
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* code.
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*
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* The code for the case where the capability is present will be
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* assembled into a special section to be used for dynamic patching.
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* Code for that case 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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/*
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* Begin an alternative code sequence.
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*/
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.macro alternative_if_not cap
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.set .Lasm_alt_mode, 0
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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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.endm
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.macro alternative_if cap
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.set .Lasm_alt_mode, 1
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.pushsection .altinstructions, "a"
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altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
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.popsection
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.pushsection .altinstr_replacement, "ax"
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.align 2 /* So GAS knows label 661 is suitably aligned */
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661:
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.endm
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.macro alternative_cb cb
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.set .Lasm_alt_mode, 0
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.pushsection .altinstructions, "a"
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altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
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.popsection
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661:
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.endm
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/*
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* Provide the other half of the alternative code sequence.
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*/
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.macro alternative_else
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662:
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.if .Lasm_alt_mode==0
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.pushsection .altinstr_replacement, "ax"
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.else
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.popsection
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.endif
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663:
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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
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664:
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.if .Lasm_alt_mode==0
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.popsection
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.endif
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.org . - (664b-663b) + (662b-661b)
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.org . - (662b-661b) + (664b-663b)
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.endm
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/*
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* Callback-based alternative epilogue
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*/
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.macro alternative_cb_end
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662:
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.endm
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/*
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* Provides a trivial alternative or default sequence consisting solely
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* of NOPs. The number of NOPs is chosen automatically to match the
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* previous case.
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*/
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.macro alternative_else_nop_endif
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alternative_else
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nops (662b-661b) / AARCH64_INSN_SIZE
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alternative_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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.macro user_alt, label, oldinstr, newinstr, cond
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9999: alternative_insn "\oldinstr", "\newinstr", \cond
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_ASM_EXTABLE 9999b, \label
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.endm
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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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