all: enable c-shared/c-archive support for freebsd/amd64

Fixes #14327
Much of the code is based on the linux/amd64 code that implements these
build modes, and code is shared where possible.

Change-Id: Ia510f2023768c0edbc863aebc585929ec593b332
Reviewed-on: https://go-review.googlesource.com/93875
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testcarchive/carchive_test.go

@@ -260,6 +260,9 @@ func TestSignalForwarding(t *testing.T) {
 }
 
 func TestSignalForwardingExternal(t *testing.T) {
+	if GOOS == "freebsd" {
+		t.Skipf("skipping on %s/%s; signal always goes to the Go runtime", GOOS, GOARCH)
+	}
 	checkSignalForwardingTest(t)
 
 	defer func() {
@@ -433,7 +436,7 @@ func TestSigaltstack(t *testing.T) {
 }
 
 const testar = `#!/usr/bin/env bash
-while expr $1 : '[-]' >/dev/null; do
+while [[ $1 == -* ]] >/dev/null; do
   shift
 done
 echo "testar" > $1

misc/cgo/testcarchive/main5.c

@@ -85,6 +85,8 @@ int main(int argc, char** argv) {
 				printf("write(2) unexpectedly succeeded\n");
 				return 0;
 			}
+			printf("did not receieve SIGPIPE\n");
+			return 0;
 		}
 		default:
 			printf("Unknown test: %d\n", test);

misc/cgo/testcshared/cshared_test.go

@@ -322,7 +322,11 @@ func TestExportedSymbolsWithDynamicLoad(t *testing.T) {
 
 	createHeadersOnce(t)
 
-	runCC(t, "-o", cmd, "main1.c", "-ldl")
+	if GOOS != "freebsd" {
+		runCC(t, "-o", cmd, "main1.c", "-ldl")
+	} else {
+		runCC(t, "-o", cmd, "main1.c")
+	}
 	adbPush(t, cmd)
 
 	defer os.Remove(bin)
@@ -411,7 +415,11 @@ func testSignalHandlers(t *testing.T, pkgname, cfile, cmd string) {
 		"-o", libname, pkgname,
 	)
 	adbPush(t, libname)
-	runCC(t, "-pthread", "-o", cmd, cfile, "-ldl")
+	if GOOS != "freebsd" {
+		runCC(t, "-pthread", "-o", cmd, cfile, "-ldl")
+	} else {
+		runCC(t, "-pthread", "-o", cmd, cfile)
+	}
 	adbPush(t, cmd)
 
 	bin := cmdToRun(cmd)

src/cmd/dist/test.go

@@ -912,6 +912,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		switch pair {
 		case "darwin-386", "darwin-amd64", "darwin-arm", "darwin-arm64",
 			"linux-amd64", "linux-386", "linux-ppc64le", "linux-s390x",
+			"freebsd-amd64",
 			"windows-amd64", "windows-386":
 			return true
 		}
@@ -920,6 +921,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		switch pair {
 		case "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le", "linux-s390x",
 			"darwin-amd64", "darwin-386",
+			"freebsd-amd64",
 			"android-arm", "android-arm64", "android-386",
 			"windows-amd64", "windows-386":
 			return true

src/cmd/go/internal/work/init.go

@@ -98,7 +98,8 @@ func buildModeInit() {
 		} else {
 			switch platform {
 			case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/ppc64le", "linux/s390x",
-				"android/amd64", "android/arm", "android/arm64", "android/386":
+				"android/amd64", "android/arm", "android/arm64", "android/386",
+				"freebsd/amd64":
 				codegenArg = "-shared"
 			case "darwin/amd64", "darwin/386":
 			case "windows/amd64", "windows/386":

src/cmd/internal/obj/x86/asm6.go

@@ -4615,7 +4615,7 @@ func (asmbuf *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
 							log.Fatalf("unknown TLS base location for %v", ctxt.Headtype)
 
 						case objabi.Hlinux,
-							objabi.Hnacl:
+							objabi.Hnacl, objabi.Hfreebsd:
 							if ctxt.Flag_shared {
 								// Note that this is not generating the same insns as the other cases.
 								//     MOV TLS, dst
@@ -4687,9 +4687,9 @@ func (asmbuf *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
 					default:
 						log.Fatalf("unknown TLS base location for %v", ctxt.Headtype)
 
-					case objabi.Hlinux:
+					case objabi.Hlinux, objabi.Hfreebsd:
 						if !ctxt.Flag_shared {
-							log.Fatalf("unknown TLS base location for linux without -shared")
+							log.Fatalf("unknown TLS base location for linux/freebsd without -shared")
 						}
 						// Note that this is not generating the same insn as the other cases.
 						//     MOV TLS, R_to

src/cmd/internal/obj/x86/obj6.go

@@ -64,7 +64,7 @@ func CanUse1InsnTLS(ctxt *obj.Link) bool {
 	switch ctxt.Headtype {
 	case objabi.Hplan9, objabi.Hwindows:
 		return false
-	case objabi.Hlinux:
+	case objabi.Hlinux, objabi.Hfreebsd:
 		return !ctxt.Flag_shared
 	}
 

src/cmd/link/internal/ld/config.go

@@ -52,6 +52,12 @@ func (mode *BuildMode) Set(s string) error {
 	case "c-archive":
 		switch objabi.GOOS {
 		case "darwin", "linux":
+		case "freebsd":
+			switch objabi.GOARCH {
+			case "amd64":
+			default:
+				return badmode()
+			}
 		case "windows":
 			switch objabi.GOARCH {
 			case "amd64", "386":

src/runtime/cgo/gcc_fatalf.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 !android,linux
+// +build !android,linux freebsd
 
 #include <stdarg.h>
 #include <stdio.h>

src/runtime/cgo/gcc_freebsd_amd64.c

@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 #include <sys/types.h>
+#include <errno.h>
 #include <sys/signalvar.h>
 #include <pthread.h>
 #include <signal.h>
@@ -16,14 +17,21 @@ static void (*setg_gcc)(void*);
 void
 x_cgo_init(G *g, void (*setg)(void*))
 {
-	pthread_attr_t attr;
+	pthread_attr_t *attr;
 	size_t size;
 
+	// Deal with memory sanitizer/clang interaction.
+	// See gcc_linux_amd64.c for details.
 	setg_gcc = setg;
-	pthread_attr_init(&attr);
-	pthread_attr_getstacksize(&attr, &size);
+	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)&attr - size + 4096;
-	pthread_attr_destroy(&attr);
+	pthread_attr_destroy(attr);
+	free(attr);
 }
 
 void
@@ -40,7 +48,6 @@ _cgo_sys_thread_start(ThreadStart *ts)
 
 	pthread_attr_init(&attr);
 	pthread_attr_getstacksize(&attr, &size);
-
 	// Leave stacklo=0 and set stackhi=size; mstart will do the rest.
 	ts->g->stackhi = size;
 	err = _cgo_try_pthread_create(&p, &attr, threadentry, ts);
@@ -48,8 +55,7 @@ _cgo_sys_thread_start(ThreadStart *ts)
 	pthread_sigmask(SIG_SETMASK, &oset, nil);
 
 	if (err != 0) {
-		fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
-		abort();
+		fatalf("pthread_create failed: %s", strerror(err));
 	}
 }
 
@@ -59,7 +65,9 @@ threadentry(void *v)
 	ThreadStart ts;
 
 	ts = *(ThreadStart*)v;
+	_cgo_tsan_acquire();
 	free(v);
+	_cgo_tsan_release();
 
 	/*
 	 * Set specific keys.

src/runtime/cgo/gcc_freebsd_sigaction.c

+// Copyright 2018 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.
+
+// +build freebsd,amd64
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <signal.h>
+
+#include "libcgo.h"
+
+// go_sigaction_t is a C version of the sigactiont struct from
+// os_freebsd.go.  This definition — and its conversion to and from struct
+// sigaction — are specific to freebsd/amd64.
+typedef struct {
+        uint32_t __bits[_SIG_WORDS];
+} go_sigset_t;
+typedef struct {
+	uintptr_t handler;
+	int32_t flags;
+	go_sigset_t mask;
+} go_sigaction_t;
+
+int32_t
+x_cgo_sigaction(intptr_t signum, const go_sigaction_t *goact, go_sigaction_t *oldgoact) {
+	int32_t ret;
+	struct sigaction act;
+	struct sigaction oldact;
+	int i;
+
+	_cgo_tsan_acquire();
+
+	memset(&act, 0, sizeof act);
+	memset(&oldact, 0, sizeof oldact);
+
+	if (goact) {
+		if (goact->flags & SA_SIGINFO) {
+			act.sa_sigaction = (void(*)(int, siginfo_t*, void*))(goact->handler);
+		} else {
+			act.sa_handler = (void(*)(int))(goact->handler);
+		}
+		sigemptyset(&act.sa_mask);
+		for (i = 0; i < 8 * sizeof(goact->mask); i++) {
+			if (goact->mask.__bits[i/32] & ((uint32_t)(1)<<(i&31))) {
+				sigaddset(&act.sa_mask, i+1);
+			}
+		}
+		act.sa_flags = goact->flags;
+	}
+
+	ret = sigaction(signum, goact ? &act : NULL, oldgoact ? &oldact : NULL);
+	if (ret == -1) {
+		// runtime.sigaction expects _cgo_sigaction to return errno on error.
+		_cgo_tsan_release();
+		return errno;
+	}
+
+	if (oldgoact) {
+		if (oldact.sa_flags & SA_SIGINFO) {
+			oldgoact->handler = (uintptr_t)(oldact.sa_sigaction);
+		} else {
+			oldgoact->handler = (uintptr_t)(oldact.sa_handler);
+		}
+		for (i = 0 ; i < _SIG_WORDS; i++) {
+			oldgoact->mask.__bits[i] = 0;
+		}
+		for (i = 0; i < 8 * sizeof(oldgoact->mask); i++) {
+			if (sigismember(&oldact.sa_mask, i+1) == 1) {
+				oldgoact->mask.__bits[i/32] |= (uint32_t)(1)<<(i&31);
+			}
+		}
+		oldgoact->flags = oldact.sa_flags;
+	}
+
+	_cgo_tsan_release();
+	return ret;
+}

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
+// +build linux,amd64 freebsd,amd64
 
 package cgo
 

src/runtime/cgo_sigaction.go

@@ -4,7 +4,7 @@
 
 // Support for memory sanitizer. See runtime/cgo/sigaction.go.
 
-// +build linux,amd64
+// +build linux,amd64 freebsd,amd64
 
 package runtime
 

src/runtime/os_freebsd.go

@@ -12,14 +12,11 @@ import (
 type mOS struct{}
 
 //go:noescape
-func thr_new(param *thrparam, size int32)
+func thr_new(param *thrparam, size int32) int32
 
 //go:noescape
 func sigaltstack(new, old *stackt)
 
-//go:noescape
-func sigaction(sig uint32, new, old *sigactiont)
-
 //go:noescape
 func sigprocmask(how int32, new, old *sigset)
 
@@ -185,13 +182,11 @@ func newosproc(mp *m, stk unsafe.Pointer) {
 		print("newosproc stk=", stk, " m=", mp, " g=", mp.g0, " thr_start=", funcPC(thr_start), " id=", mp.id, " ostk=", &mp, "\n")
 	}
 
-	// NOTE(rsc): This code is confused. stackbase is the top of the stack
-	// and is equal to stk. However, it's working, so I'm not changing it.
 	param := thrparam{
 		start_func: funcPC(thr_start),
 		arg:        unsafe.Pointer(mp),
-		stack_base: mp.g0.stack.hi,
-		stack_size: uintptr(stk) - mp.g0.stack.hi,
+		stack_base: mp.g0.stack.lo,
+		stack_size: uintptr(stk) - mp.g0.stack.lo,
 		child_tid:  unsafe.Pointer(&mp.procid),
 		parent_tid: nil,
 		tls_base:   unsafe.Pointer(&mp.tls[0]),
@@ -201,8 +196,59 @@ func newosproc(mp *m, stk unsafe.Pointer) {
 	var oset sigset
 	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
 	// TODO: Check for error.
-	thr_new(&param, int32(unsafe.Sizeof(param)))
+	ret := thr_new(&param, int32(unsafe.Sizeof(param)))
+	sigprocmask(_SIG_SETMASK, &oset, nil)
+	if ret < 0 {
+		print("runtime: failed to create new OS thread (have ", mcount(), " already; errno=", -ret, ")\n")
+		throw("newosproc")
+	}
+}
+
+// Version of newosproc that doesn't require a valid G.
+//go:nosplit
+func newosproc0(stacksize uintptr, fn unsafe.Pointer) {
+	stack := sysAlloc(stacksize, &memstats.stacks_sys)
+	if stack == nil {
+		write(2, unsafe.Pointer(&failallocatestack[0]), int32(len(failallocatestack)))
+		exit(1)
+	}
+	// This code "knows" it's being called once from the library
+	// initialization code, and so it's using the static m0 for the
+	// tls and procid (thread) pointers. thr_new() requires the tls
+	// pointers, though the tid pointers can be nil.
+	// However, newosproc0 is currently unreachable because builds
+	// utilizing c-shared/c-archive force external linking.
+	param := thrparam{
+		start_func: funcPC(fn),
+		arg:        nil,
+		stack_base: uintptr(stack), //+stacksize?
+		stack_size: stacksize,
+		child_tid:  unsafe.Pointer(&m0.procid),
+		parent_tid: nil,
+		tls_base:   unsafe.Pointer(&m0.tls[0]),
+		tls_size:   unsafe.Sizeof(m0.tls),
+	}
+
+	var oset sigset
+	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
+	ret := thr_new(&param, int32(unsafe.Sizeof(param)))
 	sigprocmask(_SIG_SETMASK, &oset, nil)
+	if ret < 0 {
+		write(2, unsafe.Pointer(&failthreadcreate[0]), int32(len(failthreadcreate)))
+		exit(1)
+	}
+}
+
+var failallocatestack = []byte("runtime: failed to allocate stack for the new OS thread\n")
+var failthreadcreate = []byte("runtime: failed to create new OS thread\n")
+
+// Called to do synchronous initialization of Go code built with
+// -buildmode=c-archive or -buildmode=c-shared.
+// None of the Go runtime is initialized.
+//go:nosplit
+//go:nowritebarrierrec
+func libpreinit() {
+	initsig(true)
 }
 
 func osinit() {
@@ -274,25 +320,20 @@ type sigactiont struct {
 	sa_mask    sigset
 }
 
+// See os_freebsd2.go, os_freebsd_amd64.go for setsig function
+
 //go:nosplit
 //go:nowritebarrierrec
-func setsig(i uint32, fn uintptr) {
+func setsigstack(i uint32) {
 	var sa sigactiont
-	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK | _SA_RESTART
-	sa.sa_mask = sigset_all
-	if fn == funcPC(sighandler) {
-		fn = funcPC(sigtramp)
+	sigaction(i, nil, &sa)
+	if sa.sa_flags&_SA_ONSTACK != 0 {
+		return
 	}
-	sa.sa_handler = fn
+	sa.sa_flags |= _SA_ONSTACK
 	sigaction(i, &sa, nil)
 }
 
-//go:nosplit
-//go:nowritebarrierrec
-func setsigstack(i uint32) {
-	throw("setsigstack")
-}
-
 //go:nosplit
 //go:nowritebarrierrec
 func getsig(i uint32) uintptr {
@@ -354,3 +395,18 @@ func sysauxv(auxv []uintptr) {
 		archauxv(tag, val)
 	}
 }
+
+// sysSigaction calls the sigaction system call.
+//go:nosplit
+func sysSigaction(sig uint32, new, old *sigactiont) {
+	// Use system stack to avoid split stack overflow on amd64
+	if asmSigaction(uintptr(sig), new, old) != 0 {
+		systemstack(func() {
+			throw("sigaction failed")
+		})
+	}
+}
+
+// asmSigaction is implemented in assembly.
+//go:noescape
+func asmSigaction(sig uintptr, new, old *sigactiont) int32

src/runtime/os_freebsd2.go

+// Copyright 2011 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.
+
+// +build freebsd,!amd64
+
+package runtime
+
+//go:nosplit
+//go:nowritebarrierrec
+func setsig(i uint32, fn uintptr) {
+	var sa sigactiont
+	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK | _SA_RESTART
+	sa.sa_mask = sigset_all
+	if fn == funcPC(sighandler) {
+		fn = funcPC(sigtramp)
+	}
+	sa.sa_handler = fn
+	sigaction(i, &sa, nil)
+}

src/runtime/os_freebsd_amd64.go

+// Copyright 2011 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.
+
+package runtime
+
+func cgoSigtramp()
+
+//go:nosplit
+//go:nowritebarrierrec
+func setsig(i uint32, fn uintptr) {
+	var sa sigactiont
+	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK | _SA_RESTART
+	sa.sa_mask = sigset_all
+	if fn == funcPC(sighandler) {
+		if iscgo {
+			fn = funcPC(cgoSigtramp)
+		} else {
+			fn = funcPC(sigtramp)
+		}
+	}
+	sa.sa_handler = fn
+	sigaction(i, &sa, nil)
+}

src/runtime/sigaction_linux.go → src/runtime/sigaction.go

@@ -2,12 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64
+// +build linux,!amd64 freebsd,!amd64
 
 package runtime
 
-// This version is used on Linux systems on which we don't use cgo to
-// call the C version of sigaction.
+// This version is used on Linux and FreeBSD systems on which we don't
+// use cgo to call the C version of sigaction.
 
 //go:nosplit
 //go:nowritebarrierrec

src/runtime/signal_unix.go

@@ -484,7 +484,10 @@ func raisebadsignal(sig uint32, c *sigctxt) {
 	// re-installing sighandler. At this point we can just
 	// return and the signal will be re-raised and caught by
 	// the default handler with the correct context.
-	if (isarchive || islibrary) && handler == _SIG_DFL && c.sigcode() != _SI_USER {
+	//
+	// On FreeBSD, the libthr sigaction code prevents
+	// this from working so we fall through to raise.
+	if GOOS != "freebsd" && (isarchive || islibrary) && handler == _SIG_DFL && c.sigcode() != _SI_USER {
 		return
 	}
 

src/runtime/sys_freebsd_386.s

@@ -19,6 +19,7 @@ TEXT runtime·sys_umtx_op(SB),NOSPLIT,$-4
 TEXT runtime·thr_new(SB),NOSPLIT,$-4
 	MOVL	$455, AX
 	INT	$0x80
+	MOVL	AX, ret+8(FP)
 	RET
 
 TEXT runtime·thr_start(SB),NOSPLIT,$0
@@ -211,11 +212,10 @@ TEXT runtime·nanotime(SB), NOSPLIT, $32
 	RET
 
 
-TEXT runtime·sigaction(SB),NOSPLIT,$-4
+TEXT runtime·asmSigaction(SB),NOSPLIT,$-4
 	MOVL	$416, AX
 	INT	$0x80
-	JAE	2(PC)
-	MOVL	$0xf1, 0xf1  // crash
+	MOVL	AX, ret+12(FP)
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$12-16

src/runtime/sys_freebsd_amd64.s

@@ -26,6 +26,7 @@ TEXT runtime·thr_new(SB),NOSPLIT,$0
 	MOVL size+8(FP), SI
 	MOVL $455, AX
 	SYSCALL
+	MOVL	AX, ret+16(FP)
 	RET
 
 TEXT runtime·thr_start(SB),NOSPLIT,$0
@@ -169,14 +170,27 @@ TEXT runtime·nanotime(SB), NOSPLIT, $32
 	MOVQ	AX, ret+0(FP)
 	RET
 
-TEXT runtime·sigaction(SB),NOSPLIT,$-8
-	MOVL	sig+0(FP), DI		// arg 1 sig
+TEXT runtime·asmSigaction(SB),NOSPLIT,$0
+	MOVQ	sig+0(FP), DI		// arg 1 sig
 	MOVQ	new+8(FP), SI		// arg 2 act
 	MOVQ	old+16(FP), DX		// arg 3 oact
 	MOVL	$416, AX
 	SYSCALL
 	JCC	2(PC)
-	MOVL	$0xf1, 0xf1  // crash
+	MOVL	$-1, AX
+	MOVL	AX, ret+24(FP)
+	RET
+
+TEXT runtime·callCgoSigaction(SB),NOSPLIT,$16
+	MOVQ	sig+0(FP), DI		// arg 1 sig
+	MOVQ	new+8(FP), SI		// arg 2 act
+	MOVQ	old+16(FP), DX		// arg 3 oact
+	MOVQ	_cgo_sigaction(SB), AX
+	MOVQ	SP, BX			// callee-saved
+	ANDQ	$~15, SP		// alignment as per amd64 psABI
+	CALL	AX
+	MOVQ	BX, SP
+	MOVL	AX, ret+24(FP)
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
@@ -216,6 +230,82 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$72
 	MOVQ	bx-8(SP),   BX
 	RET
 
+// Used instead of sigtramp in programs that use cgo.
+// Arguments from kernel are in DI, SI, DX.
+TEXT runtime·cgoSigtramp(SB),NOSPLIT,$0
+	// If no traceback function, do usual sigtramp.
+	MOVQ	runtime·cgoTraceback(SB), AX
+	TESTQ	AX, AX
+	JZ	sigtramp
+
+	// If no traceback support function, which means that
+	// runtime/cgo was not linked in, do usual sigtramp.
+	MOVQ	_cgo_callers(SB), AX
+	TESTQ	AX, AX
+	JZ	sigtramp
+
+	// Figure out if we are currently in a cgo call.
+	// If not, just do usual sigtramp.
+	get_tls(CX)
+	MOVQ	g(CX),AX
+	TESTQ	AX, AX
+	JZ	sigtrampnog     // g == nil
+	MOVQ	g_m(AX), AX
+	TESTQ	AX, AX
+	JZ	sigtramp        // g.m == nil
+	MOVL	m_ncgo(AX), CX
+	TESTL	CX, CX
+	JZ	sigtramp        // g.m.ncgo == 0
+	MOVQ	m_curg(AX), CX
+	TESTQ	CX, CX
+	JZ	sigtramp        // g.m.curg == nil
+	MOVQ	g_syscallsp(CX), CX
+	TESTQ	CX, CX
+	JZ	sigtramp        // g.m.curg.syscallsp == 0
+	MOVQ	m_cgoCallers(AX), R8
+	TESTQ	R8, R8
+	JZ	sigtramp        // g.m.cgoCallers == nil
+	MOVL	m_cgoCallersUse(AX), CX
+	TESTL	CX, CX
+	JNZ	sigtramp	// g.m.cgoCallersUse != 0
+
+	// Jump to a function in runtime/cgo.
+	// That function, written in C, will call the user's traceback
+	// function with proper unwind info, and will then call back here.
+	// The first three arguments, and the fifth, are already in registers.
+	// Set the two remaining arguments now.
+	MOVQ	runtime·cgoTraceback(SB), CX
+	MOVQ	$runtime·sigtramp(SB), R9
+	MOVQ	_cgo_callers(SB), AX
+	JMP	AX
+
+sigtramp:
+	JMP	runtime·sigtramp(SB)
+
+sigtrampnog:
+	// Signal arrived on a non-Go thread. If this is SIGPROF, get a
+	// stack trace.
+	CMPL	DI, $27 // 27 == SIGPROF
+	JNZ	sigtramp
+
+	// Lock sigprofCallersUse.
+	MOVL	$0, AX
+	MOVL	$1, CX
+	MOVQ	$runtime·sigprofCallersUse(SB), R11
+	LOCK
+	CMPXCHGL	CX, 0(R11)
+	JNZ	sigtramp  // Skip stack trace if already locked.
+
+	// Jump to the traceback function in runtime/cgo.
+	// It will call back to sigprofNonGo, which will ignore the
+	// arguments passed in registers.
+	// First three arguments to traceback function are in registers already.
+	MOVQ	runtime·cgoTraceback(SB), CX
+	MOVQ	$runtime·sigprofCallers(SB), R8
+	MOVQ	$runtime·sigprofNonGo(SB), R9
+	MOVQ	_cgo_callers(SB), AX
+	JMP	AX
+
 TEXT runtime·mmap(SB),NOSPLIT,$0
 	MOVQ	addr+0(FP), DI		// arg 1 addr
 	MOVQ	n+8(FP), SI		// arg 2 len

src/runtime/sys_freebsd_arm.s

@@ -59,6 +59,7 @@ TEXT runtime·thr_new(SB),NOSPLIT,$0
 	MOVW size+4(FP), R1
 	MOVW $SYS_thr_new, R7
 	SWI $0
+	MOVW	R0, ret+8(FP)
 	RET
 
 TEXT runtime·thr_start(SB),NOSPLIT,$0
@@ -207,14 +208,14 @@ TEXT runtime·nanotime(SB), NOSPLIT, $32
 	MOVW R1, ret_hi+4(FP)
 	RET
 
-TEXT runtime·sigaction(SB),NOSPLIT|NOFRAME,$0
+TEXT runtime·asmSigaction(SB),NOSPLIT|NOFRAME,$0
 	MOVW sig+0(FP), R0		// arg 1 sig
 	MOVW new+4(FP), R1		// arg 2 act
 	MOVW old+8(FP), R2		// arg 3 oact
 	MOVW $SYS_sigaction, R7
 	SWI $0
-	MOVW.CS $0, R8 // crash on syscall failure
-	MOVW.CS R8, (R8)
+	MOVW.CS	$-1, R0
+	MOVW	R0, ret+12(FP)
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$12