runtime/cgo: deduplicate x_cgo_init and crosscall1

Most platforms share the same implementation for x_cgo_init and
crosscall1. Solaris diverges too much and is left for a future CL.

Cq-Include-Trybots: luci.golang.try:gotip-freebsd-amd64,gotip-darwin-amd64_14,gotip-darwin-arm64_15,gotip-netbsd-arm64,gotip-openbsd-ppc64,gotip-solaris-amd64,gotip-linux-ppc64_power10
Change-Id: Ib2eeb6456caa5c055e1ac1907c2fdf63db58dafc
Reviewed-on: https://go-review.googlesource.com/c/go/+/708035
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>

15 files changed, 168 insertions, 496 deletions

diff --git a/src/runtime/cgo/gcc_darwin_amd64.c b/src/runtime/cgo/gcc_darwin_amd64.c
deleted file mode 100644
index 0a9198e29f..0000000000
--- a/src/runtime/cgo/gcc_darwin_amd64.c
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include <string.h> /* for strerror */
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
-{
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-}
-
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_dragonfly_amd64.c b/src/runtime/cgo/gcc_dragonfly_amd64.c
deleted file mode 100644
index 4851b2a6a0..0000000000
--- a/src/runtime/cgo/gcc_dragonfly_amd64.c
+++ /dev/null
@@ -1,29 +0,0 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*))
-{
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-}
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_freebsd.c b/src/runtime/cgo/gcc_freebsd.c
index b5adecc5f1..606d6bd591 100644
--- a/src/runtime/cgo/gcc_freebsd.c
+++ b/src/runtime/cgo/gcc_freebsd.c
@@ -1,41 +1,16 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build freebsd && (386 || arm || arm64 || riscv64)
-
-#include <machine/sysarch.h>
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-#ifdef ARM_TP_ADDRESS
-// ARM_TP_ADDRESS is (ARM_VECTORS_HIGH + 0x1000) or 0xffff1000
-// and is known to runtime.read_tls_fallback. Verify it with
-// cpp.
-#if ARM_TP_ADDRESS != 0xffff1000
-#error Wrong ARM_TP_ADDRESS!
-#endif
-#endif
-
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*))
-{
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-}
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	crosscall1(ts.fn, setg_gcc, ts.g);
-	return nil;
-}
+// Copyright 2009 The Go Authors. All rights reserved.

+// Use of this source code is governed by a BSD-style

+// license that can be found in the LICENSE file.

+

+//go:build freebsd

+

+#include <machine/sysarch.h>

+

+#ifdef ARM_TP_ADDRESS

+// ARM_TP_ADDRESS is (ARM_VECTORS_HIGH + 0x1000) or 0xffff1000

+// and is known to runtime.read_tls_fallback. Verify it with

+// cpp.

+#if ARM_TP_ADDRESS != 0xffff1000

+#error Wrong ARM_TP_ADDRESS!

+#endif

+#endif

diff --git a/src/runtime/cgo/gcc_freebsd_amd64.c b/src/runtime/cgo/gcc_freebsd_amd64.c
deleted file mode 100644
index 0fa81495a3..0000000000
--- a/src/runtime/cgo/gcc_freebsd_amd64.c
+++ /dev/null
@@ -1,41 +0,0 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include <errno.h>
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*))
-{
-	uintptr *pbounds;
-
-	// Deal with memory sanitizer/clang interaction.
-	// See gcc_linux_amd64.c for details.
-	setg_gcc = setg;
-	pbounds = (uintptr*)malloc(2 * sizeof(uintptr));
-	if (pbounds == NULL) {
-		fatalf("malloc failed: %s", strerror(errno));
-	}
-	_cgo_set_stacklo(g, pbounds);
-	free(pbounds);
-}
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	_cgo_tsan_acquire();
-	free(v);
-	_cgo_tsan_release();
-
-	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_darwin_arm64.c b/src/runtime/cgo/gcc_ios_arm64.c
index e502851fc1..32f517d464 100644
--- a/src/runtime/cgo/gcc_darwin_arm64.c
+++ b/src/runtime/cgo/gcc_ios_arm64.c
@@ -9,7 +9,6 @@
 #include <stdlib.h>
 
 #include "libcgo.h"
-#include "libcgo_unix.h"
 
 #include <TargetConditionals.h>
 
@@ -18,27 +17,16 @@
 #include <CoreFoundation/CFString.h>
 #endif
 
-static void (*setg_gcc)(void*);
+#if TARGET_OS_IPHONE
 
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
+static void
+threadentry_platform(void)
 {
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
 #if TARGET_OS_IPHONE
 	darwin_arm_init_thread_exception_port();
 #endif
-
-	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
-	return nil;
 }
 
-#if TARGET_OS_IPHONE
-
 // init_working_dir sets the current working directory to the app root.
 // By default ios/arm64 processes start in "/".
 static void
@@ -101,16 +89,15 @@ init_working_dir()
 
 #endif // TARGET_OS_IPHONE
 
-void
-x_cgo_init(G *g, void (*setg)(void*))
+static void
+init_platform()
 {
-	//fprintf(stderr, "x_cgo_init = %p\n", &x_cgo_init); // aid debugging in presence of ASLR
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-
 #if TARGET_OS_IPHONE
 	darwin_arm_init_mach_exception_handler();
 	darwin_arm_init_thread_exception_port();
 	init_working_dir();
 #endif
 }
+
+void (*x_cgo_init_platform)(void) = init_platform;
+void (*x_cgo_threadentry_platform)(void) = threadentry_platform;
diff --git a/src/runtime/cgo/gcc_libinit.c b/src/runtime/cgo/gcc_libinit.c
index 4b163c2d19..9d2402636e 100644
--- a/src/runtime/cgo/gcc_libinit.c
+++ b/src/runtime/cgo/gcc_libinit.c
@@ -83,30 +83,6 @@ _cgo_wait_runtime_init_done(void) {
 	return 0;
 }
 
-// _cgo_set_stacklo sets g->stacklo based on the stack size.
-// This is common code called from x_cgo_init, which is itself
-// called by rt0_go in the runtime package.
-void _cgo_set_stacklo(G *g, uintptr *pbounds)
-{
-	uintptr bounds[2];
-
-	// pbounds can be passed in by the caller; see gcc_linux_amd64.c.
-	if (pbounds == NULL) {
-		pbounds = &bounds[0];
-	}
-
-	x_cgo_getstackbound(pbounds);
-
-	g->stacklo = *pbounds;
-
-	// Sanity check the results now, rather than getting a
-	// morestack on g0 crash.
-	if (g->stacklo >= g->stackhi) {
-		fprintf(stderr, "runtime/cgo: bad stack bounds: lo=%p hi=%p\n", (void*)(g->stacklo), (void*)(g->stackhi));
-		abort();
-	}
-}
-
 // Store the g into a thread-specific value associated with the pthread key pthread_g.
 // And pthread_key_destructor will dropm when the thread is exiting.
 void x_cgo_bindm(void* g) {
diff --git a/src/runtime/cgo/gcc_linux.c b/src/runtime/cgo/gcc_linux.c
deleted file mode 100644
index cdccbf3454..0000000000
--- a/src/runtime/cgo/gcc_linux.c
+++ /dev/null
@@ -1,37 +0,0 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build linux && (386 || arm || loong64 || mips || mipsle || mips64 || mips64le || riscv64)
-
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((common));
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
-{
-	setg_gcc = setg;
-
-	_cgo_set_stacklo(g, NULL);
-
-	if (x_cgo_inittls) {
-		x_cgo_inittls(tlsg, tlsbase);
-	}
-}
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	crosscall1(ts.fn, setg_gcc, ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_linux_amd64.c b/src/runtime/cgo/gcc_linux_amd64.c
deleted file mode 100644
index 35c4f76457..0000000000
--- a/src/runtime/cgo/gcc_linux_amd64.c
+++ /dev/null
@@ -1,63 +0,0 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include <errno.h>
-#include <string.h> // strerror
-#include <stdlib.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-static void (*setg_gcc)(void*);
-
-// This will be set in gcc_android.c for android-specific customization.
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((common));
-
-void
-x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
-{
-	uintptr *pbounds;
-
-	/* 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;
-	pbounds = (uintptr*)malloc(2 * sizeof(uintptr));
-	if (pbounds == NULL) {
-		fatalf("malloc failed: %s", strerror(errno));
-	}
-	_cgo_set_stacklo(g, pbounds);
-	free(pbounds);
-
-	if (x_cgo_inittls) {
-		x_cgo_inittls(tlsg, tlsbase);
-	}
-}
-
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	_cgo_tsan_acquire();
-	free(v);
-	_cgo_tsan_release();
-
-	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_linux_arm64.c b/src/runtime/cgo/gcc_linux_arm64.c
deleted file mode 100644
index bd4b36a553..0000000000
--- a/src/runtime/cgo/gcc_linux_arm64.c
+++ /dev/null
@@ -1,58 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include <errno.h>
-#include <string.h>
-#include <stdlib.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((common));
-static void (*setg_gcc)(void*);
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
-	return nil;
-}
-
-void
-x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
-{
-	uintptr *pbounds;
-
-	/* 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;
-	pbounds = (uintptr*)malloc(2 * sizeof(uintptr));
-	if (pbounds == NULL) {
-		fatalf("malloc failed: %s", strerror(errno));
-	}
-	_cgo_set_stacklo(g, pbounds);
-	free(pbounds);
-
-	if (x_cgo_inittls) {
-		x_cgo_inittls(tlsg, tlsbase);
-	}
-}
diff --git a/src/runtime/cgo/gcc_linux_s390x.c b/src/runtime/cgo/gcc_linux_s390x.c
deleted file mode 100644
index 8f055e3087..0000000000
--- a/src/runtime/cgo/gcc_linux_s390x.c
+++ /dev/null
@@ -1,34 +0,0 @@
-// Copyright 2016 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase);
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*), void **tlsbase)
-{
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-}
-
-extern void crosscall_s390x(void (*fn)(void), void *g);
-
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	// Save g for this thread in C TLS
-	setg_gcc((void*)ts.g);
-
-	crosscall_s390x(ts.fn, (void*)ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_netbsd.c b/src/runtime/cgo/gcc_netbsd.c
index c8c0969108..4e92c86f86 100644
--- a/src/runtime/cgo/gcc_netbsd.c
+++ b/src/runtime/cgo/gcc_netbsd.c
@@ -1,44 +1,26 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build netbsd && (386 || amd64 || arm || arm64)
-
-#include <signal.h>
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*))
-{
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-}
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-	stack_t ss;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	// On NetBSD, a new thread inherits the signal stack of the
-	// creating thread. That confuses minit, so we remove that
-	// signal stack here before calling the regular mstart. It's
-	// a bit baroque to remove a signal stack here only to add one
-	// in minit, but it's a simple change that keeps NetBSD
-	// working like other OS's. At this point all signals are
-	// blocked, so there is no race.
-	memset(&ss, 0, sizeof ss);
-	ss.ss_flags = SS_DISABLE;
-	sigaltstack(&ss, nil);
-
-	crosscall1(ts.fn, setg_gcc, ts.g);
-	return nil;
-}
+// Copyright 2009 The Go Authors. All rights reserved.

+// Use of this source code is governed by a BSD-style

+// license that can be found in the LICENSE file.

+

+//go:build netbsd

+

+#include <string.h>

+#include <signal.h>

+

+static void

+threadentry_platform(void)

+{

+	// On NetBSD, a new thread inherits the signal stack of the

+	// creating thread. That confuses minit, so we remove that

+	// signal stack here before calling the regular mstart. It's

+	// a bit baroque to remove a signal stack here only to add one

+	// in minit, but it's a simple change that keeps NetBSD

+	// working like other OS's. At this point all signals are

+	// blocked, so there is no race.

+	stack_t ss;

+	memset(&ss, 0, sizeof ss);

+	ss.ss_flags = SS_DISABLE;

+	sigaltstack(&ss, NULL);

+}

+

+void (*x_cgo_threadentry_platform)(void) = threadentry_platform;

diff --git a/src/runtime/cgo/gcc_openbsd.c b/src/runtime/cgo/gcc_openbsd.c
deleted file mode 100644
index 166b9cd756..0000000000
--- a/src/runtime/cgo/gcc_openbsd.c
+++ /dev/null
@@ -1,31 +0,0 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build openbsd && (386 || arm || amd64 || arm64 || riscv64)
-
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*))
-{
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-}
-
-extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	free(v);
-
-	crosscall1(ts.fn, setg_gcc, ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_ppc64x.c b/src/runtime/cgo/gcc_ppc64x.c
deleted file mode 100644
index 6f5a0bd9ad..0000000000
--- a/src/runtime/cgo/gcc_ppc64x.c
+++ /dev/null
@@ -1,38 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build ppc64 || ppc64le
-
-#include <string.h>
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase);
-static void (*setg_gcc)(void*);
-
-void
-x_cgo_init(G *g, void (*setg)(void*), void **tlsbase)
-{
-	setg_gcc = setg;
-	_cgo_set_stacklo(g, NULL);
-}
-
-extern void crosscall_ppc64(void (*fn)(void), void *g);
-
-void*
-threadentry(void *v)
-{
-	ThreadStart ts;
-
-	ts = *(ThreadStart*)v;
-	_cgo_tsan_acquire();
-	free(v);
-	_cgo_tsan_release();
-
-	// Save g for this thread in C TLS
-	setg_gcc((void*)ts.g);
-
-	crosscall_ppc64(ts.fn, (void*)ts.g);
-	return nil;
-}
diff --git a/src/runtime/cgo/gcc_unix.c b/src/runtime/cgo/gcc_unix.c
new file mode 100644
index 0000000000..6004f8ca11
--- /dev/null
+++ b/src/runtime/cgo/gcc_unix.c
@@ -0,0 +1,118 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix && !solaris
+
+#include <signal.h>
+#include <string.h>
+#include <errno.h>
+#include "libcgo.h"
+#include "libcgo_unix.h"
+
+// Platform-specific hooks.
+void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((weak));
+void (*x_cgo_init_platform)(void) __attribute__((weak));
+void (*x_cgo_threadentry_platform)(void) __attribute__((weak));
+
+static void (*setg_gcc)(void*);
+
+// _cgo_set_stacklo sets g->stacklo based on the stack size.
+// This is common code called from x_cgo_init, which is itself
+// called by rt0_go in the runtime package.
+static void
+_cgo_set_stacklo(G *g)
+{
+	uintptr bounds[2];
+
+	x_cgo_getstackbound(bounds);
+
+	g->stacklo = bounds[0];
+
+	// Sanity check the results now, rather than getting a
+	// morestack on g0 crash.
+	if (g->stacklo >= g->stackhi) {
+		fprintf(stderr, "runtime/cgo: bad stack bounds: lo=%p hi=%p\n", (void*)(g->stacklo), (void*)(g->stackhi));
+		abort();
+	}
+}
+
+static void
+clang_init()
+{
+#if defined(__linux__) && (defined(__x86_64__) || defined(__aarch64__))
+	/* 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
+	   cmd/cgo/internal/testsanitizers .  */
+	uintptr *p;
+	p = (uintptr*)malloc(sizeof(uintptr));
+	if (p == NULL) {
+		fatalf("malloc failed: %s", strerror(errno));
+	}
+	/* GCC works hard to eliminate a seemingly unnecessary call to
+	   malloc, so we actually touch the memory we allocate.  */
+	((volatile char *)p)[0] = 0;
+	free(p);
+#endif
+}
+
+void
+x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
+{
+	clang_init();
+	setg_gcc = setg;
+	_cgo_set_stacklo(g);
+
+	if (x_cgo_inittls) {
+		x_cgo_inittls(tlsg, tlsbase);
+	}
+	if (x_cgo_init_platform) {
+		x_cgo_init_platform();
+	}
+}
+
+// TODO: change crosscall_ppc64 and crosscall_s390x so that it matches crosscall1
+// signature and behavior.
+#if defined(__powerpc64__)
+extern void crosscall_ppc64(void (*fn)(void), void *g);
+#elif defined(__s390x__)
+extern void crosscall_s390x(void (*fn)(void), void *g);
+#else
+extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
+#endif
+
+void*
+threadentry(void *v)
+{
+	ThreadStart ts;
+
+	ts = *(ThreadStart*)v;
+	_cgo_tsan_acquire();
+	free(v);
+	_cgo_tsan_release();
+
+	if (x_cgo_threadentry_platform != NULL) {
+		x_cgo_threadentry_platform();
+	}
+
+#if defined(__powerpc64__)
+	// Save g for this thread in C TLS
+	setg_gcc((void*)ts.g);
+	crosscall_ppc64(ts.fn, (void*)ts.g);
+#elif defined(__s390x__)
+	// Save g for this thread in C TLS
+	setg_gcc((void*)ts.g);
+	crosscall_s390x(ts.fn, (void*)ts.g);
+#else
+	crosscall1(ts.fn, setg_gcc, ts.g);
+#endif
+	return NULL;
+}
diff --git a/src/runtime/cgo/libcgo_unix.h b/src/runtime/cgo/libcgo_unix.h
index 5ce0224523..604fd5dc1b 100644
--- a/src/runtime/cgo/libcgo_unix.h
+++ b/src/runtime/cgo/libcgo_unix.h
@@ -5,11 +5,6 @@
 #include <pthread.h>
 
 /*
- * Initialize g->stacklo.
- */
-extern void _cgo_set_stacklo(G *, uintptr *);
-
-/*
  * Call pthread_create, retrying on EAGAIN.
  */
 extern int _cgo_try_pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*);