4d3b57da15
Our userspace <linux/compiler.h> defines READ_ONCE() in a way that clang
doesn't like, as we have an anonymous union in which neither field is
initialized.
WRITE_ONCE() is fine since it initializes the __val field. For
READ_ONCE() we can keep clang and GCC happy with a dummy initialization
of the __c field, so let's do that.
At the same time, let's split READ_ONCE() and WRITE_ONCE() over several
lines for legibility, as we do in the in-kernel <linux/compiler.h>.
Reported-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Reported-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Tested-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 6aa7de0591 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
Link: http://lkml.kernel.org/r/20180404163445.16492-1-mark.rutland@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
176 lines
4.6 KiB
C
176 lines
4.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _TOOLS_LINUX_COMPILER_H_
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#define _TOOLS_LINUX_COMPILER_H_
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#ifdef __GNUC__
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#include <linux/compiler-gcc.h>
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#endif
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#ifndef __compiletime_error
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# define __compiletime_error(message)
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#endif
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/* Optimization barrier */
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/* The "volatile" is due to gcc bugs */
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#define barrier() __asm__ __volatile__("": : :"memory")
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#ifndef __always_inline
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# define __always_inline inline __attribute__((always_inline))
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#endif
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#ifndef noinline
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#define noinline
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#endif
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/* Are two types/vars the same type (ignoring qualifiers)? */
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#ifndef __same_type
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# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
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#endif
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#ifdef __ANDROID__
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/*
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* FIXME: Big hammer to get rid of tons of:
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* "warning: always_inline function might not be inlinable"
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*
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* At least on android-ndk-r12/platforms/android-24/arch-arm
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*/
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#undef __always_inline
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#define __always_inline inline
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#endif
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#define __user
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#define __rcu
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#define __read_mostly
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#ifndef __attribute_const__
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# define __attribute_const__
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#endif
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#ifndef __maybe_unused
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# define __maybe_unused __attribute__((unused))
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#endif
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#ifndef __used
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# define __used __attribute__((__unused__))
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#endif
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#ifndef __packed
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# define __packed __attribute__((__packed__))
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#endif
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#ifndef __force
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# define __force
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#endif
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#ifndef __weak
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# define __weak __attribute__((weak))
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#endif
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#ifndef likely
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# define likely(x) __builtin_expect(!!(x), 1)
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#endif
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#ifndef unlikely
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# define unlikely(x) __builtin_expect(!!(x), 0)
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#endif
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#ifndef __init
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# define __init
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#endif
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#ifndef noinline
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# define noinline
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#endif
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#define uninitialized_var(x) x = *(&(x))
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#include <linux/types.h>
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/*
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* Following functions are taken from kernel sources and
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* break aliasing rules in their original form.
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*
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* While kernel is compiled with -fno-strict-aliasing,
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* perf uses -Wstrict-aliasing=3 which makes build fail
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* under gcc 4.4.
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*
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* Using extra __may_alias__ type to allow aliasing
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* in this case.
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*/
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typedef __u8 __attribute__((__may_alias__)) __u8_alias_t;
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typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
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typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
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typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;
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static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
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{
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switch (size) {
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case 1: *(__u8_alias_t *) res = *(volatile __u8_alias_t *) p; break;
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case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
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case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
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case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
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default:
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barrier();
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__builtin_memcpy((void *)res, (const void *)p, size);
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barrier();
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}
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}
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static __always_inline void __write_once_size(volatile void *p, void *res, int size)
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{
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switch (size) {
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case 1: *(volatile __u8_alias_t *) p = *(__u8_alias_t *) res; break;
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case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
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case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
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case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
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default:
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barrier();
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__builtin_memcpy((void *)p, (const void *)res, size);
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barrier();
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}
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}
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/*
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* Prevent the compiler from merging or refetching reads or writes. The
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* compiler is also forbidden from reordering successive instances of
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* READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
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* particular ordering. One way to make the compiler aware of ordering is to
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* put the two invocations of READ_ONCE or WRITE_ONCE in different C
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* statements.
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*
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* These two macros will also work on aggregate data types like structs or
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* unions. If the size of the accessed data type exceeds the word size of
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* the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
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* fall back to memcpy and print a compile-time warning.
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*
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* Their two major use cases are: (1) Mediating communication between
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* process-level code and irq/NMI handlers, all running on the same CPU,
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* and (2) Ensuring that the compiler does not fold, spindle, or otherwise
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* mutilate accesses that either do not require ordering or that interact
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* with an explicit memory barrier or atomic instruction that provides the
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* required ordering.
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*/
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#define READ_ONCE(x) \
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({ \
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union { typeof(x) __val; char __c[1]; } __u = \
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{ .__c = { 0 } }; \
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__read_once_size(&(x), __u.__c, sizeof(x)); \
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__u.__val; \
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})
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#define WRITE_ONCE(x, val) \
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({ \
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union { typeof(x) __val; char __c[1]; } __u = \
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{ .__val = (val) }; \
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__write_once_size(&(x), __u.__c, sizeof(x)); \
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__u.__val; \
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})
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#ifndef __fallthrough
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# define __fallthrough
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#endif
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#endif /* _TOOLS_LINUX_COMPILER_H */
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