runtime: enable memory sanitizer on arm64

Changes include:
1. open compilation option -msan for arm64
2. modify doc to explain -msan is also supported on linux/arm64
3. wrap msan lib API in msan_arm64.s
4. use libc for sigaction syscalls when cgo is enabled
5. use libc for mmap syscalls when cgo is enabled

Change-Id: I26ebe61ff7ce1906125f54a0182a720f9d58ec11
Reviewed-on: https://go-review.googlesource.com/109255
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

5 files changed, 31 insertions, 9 deletions

diff --git a/src/runtime/cgo/gcc_linux_arm64.c b/src/runtime/cgo/gcc_linux_arm64.c
index b328407f39..8630f2f03e 100644
--- a/src/runtime/cgo/gcc_linux_arm64.c
+++ b/src/runtime/cgo/gcc_linux_arm64.c
@@ -3,8 +3,10 @@
 // license that can be found in the LICENSE file.
 
 #include <pthread.h>
+#include <errno.h>
 #include <string.h>
 #include <signal.h>
+#include <stdlib.h>
 #include "libcgo.h"
 #include "libcgo_unix.h"
 
@@ -59,14 +61,34 @@ threadentry(void *v)
 void
 x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
 {
-	pthread_attr_t attr;
+	pthread_attr_t *attr;
 	size_t size;
 
+	/* The memory sanitizer distributed with versions of clang
+	   before 3.8 has a bug: if you call mmap before malloc, mmap
+	   may return an address that is later overwritten by the msan
+	   library.  Avoid this problem by forcing a call to malloc
+	   here, before we ever call malloc.
+
+	   This is only required for the memory sanitizer, so it's
+	   unfortunate that we always run it.  It should be possible
+	   to remove this when we no longer care about versions of
+	   clang before 3.8.  The test for this is
+	   misc/cgo/testsanitizers.
+
+	   GCC works hard to eliminate a seemingly unnecessary call to
+	   malloc, so we actually use the memory we allocate.  */
+
 	setg_gcc = setg;
-	pthread_attr_init(&attr);
-	pthread_attr_getstacksize(&attr, &size);
-	g->stacklo = (uintptr)&attr - size + 4096;
-	pthread_attr_destroy(&attr);
+	attr = (pthread_attr_t*)malloc(sizeof *attr);
+	if (attr == NULL) {
+		fatalf("malloc failed: %s", strerror(errno));
+	}
+	pthread_attr_init(attr);
+	pthread_attr_getstacksize(attr, &size);
+	g->stacklo = (uintptr)&size - size + 4096;
+	pthread_attr_destroy(attr);
+	free(attr);
 
 	if (x_cgo_inittls) {
 		x_cgo_inittls(tlsg, tlsbase);
diff --git a/src/runtime/cgo/gcc_mmap.c b/src/runtime/cgo/gcc_mmap.c
index 5cf6bdf8cf..e6a621d5a3 100644
--- a/src/runtime/cgo/gcc_mmap.c
+++ b/src/runtime/cgo/gcc_mmap.c
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,amd64
+// +build linux,amd64 linux,arm64
 
 #include <errno.h>
 #include <stdint.h>
diff --git a/src/runtime/cgo/gcc_sigaction.c b/src/runtime/cgo/gcc_sigaction.c
index 72fb08d720..05dee2affe 100644
--- a/src/runtime/cgo/gcc_sigaction.c
+++ b/src/runtime/cgo/gcc_sigaction.c
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,amd64
+// +build linux,amd64 linux,arm64
 
 #include <errno.h>
 #include <stddef.h>
diff --git a/src/runtime/cgo/mmap.go b/src/runtime/cgo/mmap.go
index ad5f6df70a..00fb7fced6 100644
--- a/src/runtime/cgo/mmap.go
+++ b/src/runtime/cgo/mmap.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,amd64
+// +build linux,amd64 linux,arm64
 
 package cgo
 
diff --git a/src/runtime/cgo/sigaction.go b/src/runtime/cgo/sigaction.go
index e25f4ff2f3..076fbc1a0a 100644
--- a/src/runtime/cgo/sigaction.go
+++ b/src/runtime/cgo/sigaction.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,amd64 freebsd,amd64
+// +build linux,amd64 freebsd,amd64 linux,arm64
 
 package cgo