internal/tsan_assist.h: add tsan_ld_acq and tsan_st_rel.

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
(Merged from https://github.com/openssl/openssl/pull/6996)

include/internal/tsan_assist.h

@@ -8,8 +8,9 @@
  */
  
 /*
- * Goal here is to facilitate writing "thread-opportunistic" code that
- * withstands Thread Sanitizer's scrutiny. "Thread-opportunistic" is when
+ * Contemporary compilers implement lock-free atomic memory access
+ * primitives that facilitate writing "thread-opportunistic" or even real
+ * multi-threading low-overhead code. "Thread-opportunistic" is when
  * exact result is not required, e.g. some statistics, or execution flow
  * doesn't have to be unambiguous. Simplest example is lazy "constant"
  * initialization when one can synchronize on variable itself, e.g.
@@ -28,12 +29,22 @@
  * bother. Having Thread Sanitizer accept "thread-opportunistic" code
  * allows to move on trouble-shooting real bugs.
  *
- * We utilize the fact that compilers that implement Thread Sanitizer
- * implement even atomic operations. Then it's assumed that
- * ATOMIC_{LONG|INT}_LOCK_FREE are assigned same value as
- * ATOMIC_POINTER_LOCK_FREE. And check for >= 2 ensures that correspodning
+ * Resolving Thread Sanitizer nits was the initial purpose for this module,
+ * but it was later extended with more nuanced primitives that are useful
+ * even in "non-opportunistic" scenarios. Most notably verifying if a shared
+ * structure is fully initialized and bypassing the initialization lock.
+ * It's suggested to view macros defined in this module as "annotations" for
+ * thread-safe lock-free code, "Thread-Safe ANnotations"...
+ *
+ * It's assumed that ATOMIC_{LONG|INT}_LOCK_FREE are assigned same value as
+ * ATOMIC_POINTER_LOCK_FREE. And check for >= 2 ensures that corresponding
  * code is inlined. It should be noted that statistics counters become
  * accurate in such case.
+ *
+ * Special note about TSAN_QUALIFIER. It might be undesired to use it in
+ * a shared header. Because whether operation on specific variable or member
+ * is atomic or not might be irrelevant in other modules. In such case one
+ * can use TSAN_QUALIFIER in cast specifically when it has to count.
  */
 
 #if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L \
@@ -46,6 +57,8 @@
 #  define tsan_load(ptr) atomic_load_explicit((ptr), memory_order_relaxed)
 #  define tsan_store(ptr, val) atomic_store_explicit((ptr), (val), memory_order_relaxed)
 #  define tsan_counter(ptr) atomic_fetch_add_explicit((ptr), 1, memory_order_relaxed)
+#  define tsan_ld_acq(ptr) atomic_load_explicit((ptr), memory_order_acquire)
+#  define tsan_st_rel(ptr, val) atomic_store_explicit((ptr), (val), memory_order_release)
 # endif
 
 #elif defined(__GNUC__) && defined(__ATOMIC_RELAXED)
@@ -56,21 +69,57 @@
 #  define tsan_load(ptr) __atomic_load_n((ptr), __ATOMIC_RELAXED)
 #  define tsan_store(ptr, val) __atomic_store_n((ptr), (val), __ATOMIC_RELAXED)
 #  define tsan_counter(ptr) __atomic_fetch_add((ptr), 1, __ATOMIC_RELAXED)
+#  define tsan_ld_acq(ptr) __atomic_load_n((ptr), __ATOMIC_ACQUIRE)
+#  define tsan_st_rel(ptr, val) __atomic_store_n((ptr), (val), __ATOMIC_RELEASE)
 # endif
 
-#elif defined(_MSC_VER) && _MSC_VER>=1200
-
+#elif defined(_MSC_VER) && _MSC_VER>=1200 \
+      && (defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64) || \
+          defined(_M_ARM64) || (defined(_M_ARM) && _M_ARM >= 7))
+/*
+ * There is subtle dependency on /volatile:<iso|ms> command-line option.
+ * "ms" implies same semantic as memory_order_acquire for loads and
+ * memory_order_release for stores, while "iso" - memory_order_relaxed for
+ * either. Real complication is that defaults are different on x86 and ARM.
+ * There is explanation for that, "ms" is backward compatible with earlier
+ * compiler versions, while multi-processor ARM can be viewed as brand new
+ * platform to MSC and its users, and with non-relaxed semantic taking toll
+ * with additional instructions and penalties, it kind of makes sense to
+ * default to "iso"...
+ */
 # define TSAN_QUALIFIER volatile
-# define tsan_load(ptr) (*(ptr))
-# define tsan_store(ptr, val) (*(ptr) = (val))
+# if defined(_M_ARM) || defined(_M_ARM64)
+#  define _InterlockedExchangeAdd _InterlockedExchangeAdd_nf
+#  pragma intrinsic(_InterlockedExchangeAdd_nf)
+#  pragma intrinsic(__iso_volatile_load32, __iso_volatile_store32)
+#  ifdef _WIN64
+#   define _InterlockedExchangeAdd64 _InterlockedExchangeAdd64_nf
+#   pragma intrinsic(_InterlockedExchangeAdd64_nf)
+#   pragma intrinsic(__iso_volatile_load64, __iso_volatile_store64)
+#   define tsan_load(ptr) (sizeof(*(ptr)) == 8 ? __iso_volatile_load64(ptr) \
+                                               : __iso_volatile_load32(ptr))
+#   define tsan_store(ptr, val) (sizeof(*(ptr)) == 8 ? __iso_volatile_store64((ptr), (val)) \
+                                                     : __iso_volatile_store32((ptr), (val)))
+#  else
+#   define tsan_load(ptr) __iso_volatile_load32(ptr)
+#   define tsan_store(ptr, val) __iso_volatile_store32((ptr), (val))
+#  endif
+# else
+#  define tsan_load(ptr) (*(ptr))
+#  define tsan_store(ptr, val) (*(ptr) = (val))
+# endif
 # pragma intrinsic(_InterlockedExchangeAdd)
 # ifdef _WIN64
 #  pragma intrinsic(_InterlockedExchangeAdd64)
-#  define tsan_counter(ptr) (sizeof(*ptr) == 8 ? _InterlockedExchangeAdd64((ptr), 1) \
-                                               : _InterlockedExchangeAdd((ptr), 1))
+#  define tsan_counter(ptr) (sizeof(*(ptr)) == 8 ? _InterlockedExchangeAdd64((ptr), 1) \
+                                                 : _InterlockedExchangeAdd((ptr), 1))
 # else
 #  define tsan_counter(ptr) _InterlockedExchangeAdd((ptr), 1)
 # endif
+# if !defined(_ISO_VOLATILE)
+#  define tsan_ld_acq(ptr) (*(ptr))
+#  define tsan_st_rel(ptr, val) (*(ptr) = (val))
+# endif
 
 #endif
 
@@ -80,5 +129,10 @@
 # define tsan_load(ptr) (*(ptr))
 # define tsan_store(ptr, val) (*(ptr) = (val))
 # define tsan_counter(ptr) ((*(ptr))++)
+/*
+ * Lack of tsan_ld_acq and tsan_ld_rel means that compiler support is not
+ * sophisticated enough to support them. Code that relies on them should be
+ * protected with #ifdef tsan_ld_acq with locked fallback.
+ */
 
 #endif