tsan: Add optional support for distinguishing volatiles

Add support to optionally emit different instrumentation for accesses to
volatile variables. While the default TSAN runtime likely will never
require this feature, other runtimes for different environments that
have subtly different memory models or assumptions may require
distinguishing volatiles.

One such environment are OS kernels, where volatile is still used in
various places, and often declare volatile to be appropriate even in
multi-threaded contexts. One such example is the Linux kernel, which
implements various synchronization primitives using volatile
(READ_ONCE(), WRITE_ONCE()).

Here the Kernel Concurrency Sanitizer (KCSAN), is a runtime that uses
TSAN instrumentation but otherwise implements a very different approach
to race detection from TSAN:

	https://github.com/google/ktsan/wiki/KCSAN

Due to recent changes in requirements by the Linux kernel, KCSAN
requires that the compiler supports tsan-distinguish-volatile (among
several new requirements):

	https://lore.kernel.org/lkml/20200521142047.169334-7-elver@google.com/

gcc/
	* params.opt: Define --param=tsan-distinguish-volatile=[0,1].
	* sanitizer.def (BUILT_IN_TSAN_VOLATILE_READ1): Define new
	builtin for volatile instrumentation of reads/writes.
	(BUILT_IN_TSAN_VOLATILE_READ2): Likewise.
	(BUILT_IN_TSAN_VOLATILE_READ4): Likewise.
	(BUILT_IN_TSAN_VOLATILE_READ8): Likewise.
	(BUILT_IN_TSAN_VOLATILE_READ16): Likewise.
	(BUILT_IN_TSAN_VOLATILE_WRITE1): Likewise.
	(BUILT_IN_TSAN_VOLATILE_WRITE2): Likewise.
	(BUILT_IN_TSAN_VOLATILE_WRITE4): Likewise.
	(BUILT_IN_TSAN_VOLATILE_WRITE8): Likewise.
	(BUILT_IN_TSAN_VOLATILE_WRITE16): Likewise.
	* tsan.c (get_memory_access_decl): Argument if access is
	volatile. If param tsan-distinguish-volatile is non-zero, and
	access if volatile, return volatile instrumentation decl.
	(instrument_expr): Check if access is volatile.

gcc/testsuite/
	* c-c++-common/tsan/volatile.c: New test.

4 files changed, 109 insertions, 12 deletions

diff --git a/gcc/params.opt b/gcc/params.opt
index 4aec480..9b564bb 100644
--- a/gcc/params.opt
+++ b/gcc/params.opt
@@ -908,6 +908,10 @@ Stop reverse growth if the reverse probability of best edge is less than this th
 Common Joined UInteger Var(param_tree_reassoc_width) Param Optimization
 Set the maximum number of instructions executed in parallel in reassociated tree.  If 0, use the target dependent heuristic.
 
+-param=tsan-distinguish-volatile=
+Common Joined UInteger Var(param_tsan_distinguish_volatile) IntegerRange(0, 1) Param
+Emit special instrumentation for accesses to volatiles.
+
 -param=uninit-control-dep-attempts=
 Common Joined UInteger Var(param_uninit_control_dep_attempts) Init(1000) IntegerRange(1, 65536) Param Optimization
 Maximum number of nested calls to search for control dependencies during uninitialized variable analysis.
diff --git a/gcc/sanitizer.def b/gcc/sanitizer.def
index 11eb646..a32715d 100644
--- a/gcc/sanitizer.def
+++ b/gcc/sanitizer.def
@@ -214,6 +214,27 @@ DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_READ_RANGE, "__tsan_read_range",
 DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_WRITE_RANGE, "__tsan_write_range",
 		      BT_FN_VOID_PTR_PTRMODE, ATTR_NOTHROW_LEAF_LIST)
 
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_READ1, "__tsan_volatile_read1",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_READ2, "__tsan_volatile_read2",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_READ4, "__tsan_volatile_read4",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_READ8, "__tsan_volatile_read8",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_READ16, "__tsan_volatile_read16",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_WRITE1, "__tsan_volatile_write1",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_WRITE2, "__tsan_volatile_write2",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_WRITE4, "__tsan_volatile_write4",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_WRITE8, "__tsan_volatile_write8",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_VOLATILE_WRITE16, "__tsan_volatile_write16",
+		      BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+
 DEF_SANITIZER_BUILTIN(BUILT_IN_TSAN_ATOMIC8_LOAD,
 		      "__tsan_atomic8_load",
 		      BT_FN_I1_CONST_VPTR_INT, ATTR_NOTHROW_LEAF_LIST)
diff --git a/gcc/testsuite/c-c++-common/tsan/volatile.c b/gcc/testsuite/c-c++-common/tsan/volatile.c
new file mode 100644
index 0000000..6837992
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/tsan/volatile.c
@@ -0,0 +1,67 @@
+/* { dg-options "--param=tsan-distinguish-volatile=1 -fdump-tree-optimized" } */
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdio.h>
+
+int32_t Global4;
+volatile int32_t VolatileGlobal4;
+volatile int64_t VolatileGlobal8;
+
+static int nvolatile_reads;
+static int nvolatile_writes;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+__attribute__((no_sanitize_thread))
+void __tsan_volatile_read4(void *addr) {
+  assert(addr == &VolatileGlobal4);
+  nvolatile_reads++;
+}
+__attribute__((no_sanitize_thread))
+void __tsan_volatile_write4(void *addr) {
+  assert(addr == &VolatileGlobal4);
+  nvolatile_writes++;
+}
+__attribute__((no_sanitize_thread))
+void __tsan_volatile_read8(void *addr) {
+  assert(addr == &VolatileGlobal8);
+  nvolatile_reads++;
+}
+__attribute__((no_sanitize_thread))
+void __tsan_volatile_write8(void *addr) {
+  assert(addr == &VolatileGlobal8);
+  nvolatile_writes++;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+__attribute__((no_sanitize_thread))
+static void check() {
+  assert(nvolatile_reads == 4);
+  assert(nvolatile_writes == 4);
+}
+
+int main() {
+  Global4 = 1;
+
+  VolatileGlobal4 = 1;
+  Global4 = VolatileGlobal4;
+  VolatileGlobal4 = 1 + VolatileGlobal4;
+
+  VolatileGlobal8 = 1;
+  Global4 = (int32_t)VolatileGlobal8;
+  VolatileGlobal8 = 1 + VolatileGlobal8;
+
+  check();
+  return 0;
+}
+
+// { dg-final { scan-tree-dump-times "__tsan_volatile_read4 \\(&VolatileGlobal4" 2 "optimized" } }
+// { dg-final { scan-tree-dump-times "__tsan_volatile_read8 \\(&VolatileGlobal8" 2 "optimized" } }
+// { dg-final { scan-tree-dump-times "__tsan_volatile_write4 \\(&VolatileGlobal4" 2 "optimized" } }
+// { dg-final { scan-tree-dump-times "__tsan_volatile_write8 \\(&VolatileGlobal8" 2 "optimized" } }
diff --git a/gcc/tsan.c b/gcc/tsan.c
index 8d22a77..447accc 100644
--- a/gcc/tsan.c
+++ b/gcc/tsan.c
@@ -52,25 +52,29 @@ along with GCC; see the file COPYING3.  If not see
    void __tsan_read/writeX (void *addr);  */
 
 static tree
-get_memory_access_decl (bool is_write, unsigned size)
+get_memory_access_decl (bool is_write, unsigned size, bool volatilep)
 {
   enum built_in_function fcode;
+  int pos;
 
   if (size <= 1)
-    fcode = is_write ? BUILT_IN_TSAN_WRITE1
-		     : BUILT_IN_TSAN_READ1;
+    pos = 0;
   else if (size <= 3)
-    fcode = is_write ? BUILT_IN_TSAN_WRITE2
-		     : BUILT_IN_TSAN_READ2;
+    pos = 1;
   else if (size <= 7)
-    fcode = is_write ? BUILT_IN_TSAN_WRITE4
-		     : BUILT_IN_TSAN_READ4;
+    pos = 2;
   else if (size <= 15)
-    fcode = is_write ? BUILT_IN_TSAN_WRITE8
-		     : BUILT_IN_TSAN_READ8;
+    pos = 3;
+  else
+    pos = 4;
+
+  if (param_tsan_distinguish_volatile && volatilep)
+    fcode = is_write ? BUILT_IN_TSAN_VOLATILE_WRITE1
+		     : BUILT_IN_TSAN_VOLATILE_READ1;
   else
-    fcode = is_write ? BUILT_IN_TSAN_WRITE16
-		     : BUILT_IN_TSAN_READ16;
+    fcode = is_write ? BUILT_IN_TSAN_WRITE1
+		     : BUILT_IN_TSAN_READ1;
+  fcode = (built_in_function)(fcode + pos);
 
   return builtin_decl_implicit (fcode);
 }
@@ -204,7 +208,8 @@ instrument_expr (gimple_stmt_iterator gsi, tree expr, bool is_write)
       g = gimple_build_call (builtin_decl, 2, expr_ptr, size_int (size));
     }
   else if (rhs == NULL)
-    g = gimple_build_call (get_memory_access_decl (is_write, size),
+    g = gimple_build_call (get_memory_access_decl (is_write, size,
+						   TREE_THIS_VOLATILE (expr)),
 			   1, expr_ptr);
   else
     {