name : alternative-macros.h /* 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 */