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Diffstat (limited to 'arch/arm64/include/asm/alternative-macros.h')
| -rw-r--r-- | arch/arm64/include/asm/alternative-macros.h | 264 |
1 files changed, 264 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h new file mode 100644 index 000000000000..d328f549b1a6 --- /dev/null +++ b/arch/arm64/include/asm/alternative-macros.h @@ -0,0 +1,264 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ASM_ALTERNATIVE_MACROS_H +#define __ASM_ALTERNATIVE_MACROS_H + +#include <linux/const.h> +#include <vdso/bits.h> + +#include <asm/cpucaps.h> +#include <asm/insn-def.h> + +/* + * Binutils 2.27.0 can't handle a 'UL' suffix on constants, so for the assembly + * macros below we must use we must use `(1 << ARM64_CB_SHIFT)`. + */ +#define ARM64_CB_SHIFT 15 +#define ARM64_CB_BIT BIT(ARM64_CB_SHIFT) + +#if ARM64_NCAPS >= ARM64_CB_BIT +#error "cpucaps have overflown ARM64_CB_BIT" +#endif + +#ifndef __ASSEMBLY__ + +#include <linux/stringify.h> + +#define ALTINSTR_ENTRY(cpucap) \ + " .word 661b - .\n" /* label */ \ + " .word 663f - .\n" /* new instruction */ \ + " .hword " __stringify(cpucap) "\n" /* cpucap */ \ + " .byte 662b-661b\n" /* source len */ \ + " .byte 664f-663f\n" /* replacement len */ + +#define ALTINSTR_ENTRY_CB(cpucap, cb) \ + " .word 661b - .\n" /* label */ \ + " .word " __stringify(cb) "- .\n" /* callback */ \ + " .hword " __stringify(cpucap) "\n" /* cpucap */ \ + " .byte 662b-661b\n" /* source len */ \ + " .byte 664f-663f\n" /* replacement len */ + +/* + * alternative assembly primitive: + * + * If any of these .org directive fail, it means that insn1 and insn2 + * don't have the same length. This used to be written as + * + * .if ((664b-663b) != (662b-661b)) + * .error "Alternatives instruction length mismatch" + * .endif + * + * but most assemblers die if insn1 or insn2 have a .inst. This should + * be fixed in a binutils release posterior to 2.25.51.0.2 (anything + * containing commit 4e4d08cf7399b606 or c1baaddf8861). + * + * Alternatives with callbacks do not generate replacement instructions. + */ +#define __ALTERNATIVE_CFG(oldinstr, newinstr, cpucap, cfg_enabled) \ + ".if "__stringify(cfg_enabled)" == 1\n" \ + "661:\n\t" \ + oldinstr "\n" \ + "662:\n" \ + ".pushsection .altinstructions,\"a\"\n" \ + ALTINSTR_ENTRY(cpucap) \ + ".popsection\n" \ + ".subsection 1\n" \ + "663:\n\t" \ + newinstr "\n" \ + "664:\n\t" \ + ".org . - (664b-663b) + (662b-661b)\n\t" \ + ".org . - (662b-661b) + (664b-663b)\n\t" \ + ".previous\n" \ + ".endif\n" + +#define __ALTERNATIVE_CFG_CB(oldinstr, cpucap, cfg_enabled, cb) \ + ".if "__stringify(cfg_enabled)" == 1\n" \ + "661:\n\t" \ + oldinstr "\n" \ + "662:\n" \ + ".pushsection .altinstructions,\"a\"\n" \ + ALTINSTR_ENTRY_CB(cpucap, cb) \ + ".popsection\n" \ + "663:\n\t" \ + "664:\n\t" \ + ".endif\n" + +#define _ALTERNATIVE_CFG(oldinstr, newinstr, cpucap, cfg, ...) \ + __ALTERNATIVE_CFG(oldinstr, newinstr, cpucap, IS_ENABLED(cfg)) + +#define ALTERNATIVE_CB(oldinstr, cpucap, cb) \ + __ALTERNATIVE_CFG_CB(oldinstr, (1 << ARM64_CB_SHIFT) | (cpucap), 1, cb) +#else + +#include <asm/assembler.h> + +.macro altinstruction_entry orig_offset alt_offset cpucap orig_len alt_len + .word \orig_offset - . + .word \alt_offset - . + .hword (\cpucap) + .byte \orig_len + .byte \alt_len +.endm + +.macro alternative_insn insn1, insn2, cap, enable = 1 + .if \enable +661: \insn1 +662: .pushsection .altinstructions, "a" + altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f + .popsection + .subsection 1 +663: \insn2 +664: .org . - (664b-663b) + (662b-661b) + .org . - (662b-661b) + (664b-663b) + .previous + .endif +.endm + +/* + * Alternative sequences + * + * The code for the case where the capability is not present will be + * assembled and linked as normal. There are no restrictions on this + * code. + * + * The code for the case where the capability is present will be + * assembled into a special section to be used for dynamic patching. + * Code for that case must: + * + * 1. Be exactly the same length (in bytes) as the default code + * sequence. + * + * 2. Not contain a branch target that is used outside of the + * alternative sequence it is defined in (branches into an + * alternative sequence are not fixed up). + */ + +/* + * Begin an alternative code sequence. + */ +.macro alternative_if_not cap + .set .Lasm_alt_mode, 0 + .pushsection .altinstructions, "a" + altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f + .popsection +661: +.endm + +.macro alternative_if cap + .set .Lasm_alt_mode, 1 + .pushsection .altinstructions, "a" + altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f + .popsection + .subsection 1 + .align 2 /* So GAS knows label 661 is suitably aligned */ +661: +.endm + +.macro alternative_cb cap, cb + .set .Lasm_alt_mode, 0 + .pushsection .altinstructions, "a" + altinstruction_entry 661f, \cb, (1 << ARM64_CB_SHIFT) | \cap, 662f-661f, 0 + .popsection +661: +.endm + +/* + * Provide the other half of the alternative code sequence. + */ +.macro alternative_else +662: + .if .Lasm_alt_mode==0 + .subsection 1 + .else + .previous + .endif +663: +.endm + +/* + * Complete an alternative code sequence. + */ +.macro alternative_endif +664: + .org . - (664b-663b) + (662b-661b) + .org . - (662b-661b) + (664b-663b) + .if .Lasm_alt_mode==0 + .previous + .endif +.endm + +/* + * Callback-based alternative epilogue + */ +.macro alternative_cb_end +662: +.endm + +/* + * Provides a trivial alternative or default sequence consisting solely + * of NOPs. The number of NOPs is chosen automatically to match the + * previous case. + */ +.macro alternative_else_nop_endif +alternative_else + nops (662b-661b) / AARCH64_INSN_SIZE +alternative_endif +.endm + +#define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...) \ + alternative_insn insn1, insn2, cap, IS_ENABLED(cfg) + +#endif /* __ASSEMBLY__ */ + +/* + * Usage: asm(ALTERNATIVE(oldinstr, newinstr, cpucap)); + * + * Usage: asm(ALTERNATIVE(oldinstr, newinstr, cpucap, CONFIG_FOO)); + * N.B. If CONFIG_FOO is specified, but not selected, the whole block + * will be omitted, including oldinstr. + */ +#define ALTERNATIVE(oldinstr, newinstr, ...) \ + _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1) + +#ifndef __ASSEMBLY__ + +#include <linux/types.h> + +static __always_inline bool +alternative_has_cap_likely(const unsigned long cpucap) +{ + if (!cpucap_is_possible(cpucap)) + return false; + + asm goto( + ALTERNATIVE_CB("b %l[l_no]", %[cpucap], alt_cb_patch_nops) + : + : [cpucap] "i" (cpucap) + : + : l_no); + + return true; +l_no: + return false; +} + +static __always_inline bool +alternative_has_cap_unlikely(const unsigned long cpucap) +{ + if (!cpucap_is_possible(cpucap)) + return false; + + asm goto( + ALTERNATIVE("nop", "b %l[l_yes]", %[cpucap]) + : + : [cpucap] "i" (cpucap) + : + : l_yes); + + return false; +l_yes: + return true; +} + +#endif /* __ASSEMBLY__ */ + +#endif /* __ASM_ALTERNATIVE_MACROS_H */ |