[PATCH 17/45] C++: Turn READ_ONCE(), WRITE_ONCE() & co. into inline template functions

David Howells
2018-04-01T20:48:14Z

Turn READ_ONCE(), WRITE_ONCE() and similar into inline template functions.
This allows the source to be simplified since there doesn't need to be
magic casting and switch-statements inside macroisation.

Signed-off-by: David Howells <dhowells@redhat.com>
---

include/linux/compiler.h | 93 ++++++++++++++--------------------------------
1 file changed, 29 insertions(+), 64 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index ab4711c63601..f9be82b93e20 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -3,6 +3,8 @@
#define __LINUX_COMPILER_H

#include <linux/compiler_types.h>
+#include <linux/kasan-checks.h>
+#include <asm/barrier.h>

#ifndef __ASSEMBLY__

@@ -168,26 +170,6 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,

#include <uapi/linux/types.h>

-#define __READ_ONCE_SIZE \
-({ \
- switch (size) { \
- case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \
- case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \
- case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \
- case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \
- default: \
- barrier(); \
- __builtin_memcpy((void *)res, (const void *)p, size); \
- barrier(); \
- } \
-})
-
-static __always_inline
-void __read_once_size(const volatile void *p, void *res, int size)
-{
- __READ_ONCE_SIZE;
-}
-
#ifdef CONFIG_KASAN
/*
* We can't declare function 'inline' because __no_sanitize_address confilcts
@@ -200,26 +182,6 @@ void __read_once_size(const volatile void *p, void *res, int size)
# define __no_kasan_or_inline __always_inline
#endif

-static __no_kasan_or_inline
-void __read_once_size_nocheck(const volatile void *p, void *res, int size)
-{
- __READ_ONCE_SIZE;
-}
-
-static __always_inline void __write_once_size(volatile void *p, void *res, int size)
-{
- switch (size) {
- case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
- case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
- case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
- case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
- default:
- barrier();
- __builtin_memcpy((void *)p, (const void *)res, size);
- barrier();
- }
-}
-
/*
* Prevent the compiler from merging or refetching reads or writes. The
* compiler is also forbidden from reordering successive instances of
@@ -242,27 +204,30 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
* with an explicit memory barrier or atomic instruction that provides the
* required ordering.
*/
-#include <asm/barrier.h>
-#include <linux/kasan-checks.h>
+template <typename P>
+static inline P READ_ONCE(P &ptr)
+{
+ barrier();
+ P val = *(volatile P *)&ptr;
+ smp_read_barrier_depends(); /* Enforce dependency ordering from x */
+ return val;
+}

-#define __READ_ONCE(x, check) \
-({ \
- union { typeof(x) __val; char __c[1]; } __u; \
- if (check) \
- __read_once_size(&(x), __u.__c, sizeof(x)); \
- else \
- __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
- smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
- __u.__val; \
-})
-#define READ_ONCE(x) __READ_ONCE(x, 1)
+template <typename P>
+static __no_kasan_or_inline P READ_ONCE_NOCHECK(P &ptr)
+{
+ barrier();
+ P val = *(volatile P *)&ptr;
+ smp_read_barrier_depends(); /* Enforce dependency ordering from x */
+ return val;
+}

/*
- * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
- * to hide memory access from KASAN.
+ * This function is not 'inline' because __no_sanitize_address confilcts
+ * with inlining. Attempt to inline it may cause a build failure.
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
*/
-#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
-
static __no_kasan_or_inline
unsigned long read_word_at_a_time(const void *addr)
{
@@ -270,13 +235,13 @@ unsigned long read_word_at_a_time(const void *addr)
return *(unsigned long *)addr;
}

-#define WRITE_ONCE(x, val) \
-({ \
- union { typeof(x) __val; char __c[1]; } __u = \
- { .__val = (__force typeof(x)) (val) }; \
- __write_once_size(&(x), __u.__c, sizeof(x)); \
- __u.__val; \
-})
+template <typename P, typename T>
+static inline void WRITE_ONCE(P &ptr, T val)
+{
+ barrier();
+ *(volatile P *)&ptr = val;
+ barrier();
+}

#endif /* __KERNEL__ */