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| 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
|---|---|
| 2 | /* |
| 3 | * Copyright (C) 2020 Google LLC. |
| 4 | */ |
| 5 | #ifndef __ASM_RWONCE_H |
| 6 | #define __ASM_RWONCE_H |
| 7 | |
| 8 | #if defined(CONFIG_LTO) && !defined(__ASSEMBLER__) |
| 9 | |
| 10 | #include <linux/compiler_types.h> |
| 11 | #include <asm/alternative-macros.h> |
| 12 | |
| 13 | #ifndef BUILD_VDSO |
| 14 | |
| 15 | #define __LOAD_RCPC(sfx, regs...) \ |
| 16 | ALTERNATIVE( \ |
| 17 | "ldar" #sfx "\t" #regs, \ |
| 18 | ".arch_extension rcpc\n" \ |
| 19 | "ldapr" #sfx "\t" #regs, \ |
| 20 | ARM64_HAS_LDAPR) |
| 21 | |
| 22 | /* |
| 23 | * When building with LTO, there is an increased risk of the compiler |
| 24 | * converting an address dependency headed by a READ_ONCE() invocation |
| 25 | * into a control dependency and consequently allowing for harmful |
| 26 | * reordering by the CPU. |
| 27 | * |
| 28 | * Ensure that such transformations are harmless by overriding the generic |
| 29 | * READ_ONCE() definition with one that provides RCpc acquire semantics |
| 30 | * when building with LTO. |
| 31 | */ |
| 32 | #define __READ_ONCE(x) \ |
| 33 | ({ \ |
| 34 | typeof(&(x)) __x = &(x); \ |
| 35 | int atomic = 1; \ |
| 36 | union { __unqual_scalar_typeof(*__x) __val; char __c[1]; } __u; \ |
| 37 | switch (sizeof(x)) { \ |
| 38 | case 1: \ |
| 39 | asm volatile(__LOAD_RCPC(b, %w0, %1) \ |
| 40 | : "=r" (*(__u8 *)__u.__c) \ |
| 41 | : "Q" (*__x) : "memory"); \ |
| 42 | break; \ |
| 43 | case 2: \ |
| 44 | asm volatile(__LOAD_RCPC(h, %w0, %1) \ |
| 45 | : "=r" (*(__u16 *)__u.__c) \ |
| 46 | : "Q" (*__x) : "memory"); \ |
| 47 | break; \ |
| 48 | case 4: \ |
| 49 | asm volatile(__LOAD_RCPC(, %w0, %1) \ |
| 50 | : "=r" (*(__u32 *)__u.__c) \ |
| 51 | : "Q" (*__x) : "memory"); \ |
| 52 | break; \ |
| 53 | case 8: \ |
| 54 | asm volatile(__LOAD_RCPC(, %0, %1) \ |
| 55 | : "=r" (*(__u64 *)__u.__c) \ |
| 56 | : "Q" (*__x) : "memory"); \ |
| 57 | break; \ |
| 58 | default: \ |
| 59 | atomic = 0; \ |
| 60 | } \ |
| 61 | atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\ |
| 62 | }) |
| 63 | |
| 64 | #endif /* !BUILD_VDSO */ |
| 65 | #endif /* CONFIG_LTO && !__ASSEMBLER__ */ |
| 66 | |
| 67 | #include <asm-generic/rwonce.h> |
| 68 | |
| 69 | #endif /* __ASM_RWONCE_H */ |
| 70 |
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