go/build, runtime/cgo: cgo support for NetBSD/ARM

R=golang-dev, rsc, dave
CC=golang-dev
https://golang.org/cl/7229082

src/pkg/go/build/build.go

@@ -251,6 +251,7 @@ var cgoEnabled = map[string]bool{
 	"linux/arm":     true,
 	"netbsd/386":    true,
 	"netbsd/amd64":  true,
+	"netbsd/arm":    true,
 	"openbsd/386":   true,
 	"openbsd/amd64": true,
 	"windows/386":   true,

src/pkg/runtime/cgo/gcc_netbsd_arm.c

+// Copyright 2013 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 <sys/types.h>
+#include <pthread.h>
+#include <signal.h>
+#include <string.h>
+#include "libcgo.h"
+
+static void *threadentry(void*);
+
+// We have to resort to TLS variable to save g(R10) and
+// m(R9). One reason is that external code might trigger
+// SIGSEGV, and our runtime.sigtramp don't even know we
+// are in external code, and will continue to use R10/R9,
+// this might as well result in another SIGSEGV.
+// Note: all three functions will clobber R0, and the last
+// two can be called from 5c ABI code.
+void __aeabi_read_tp(void) __attribute__((naked));
+void cgo_tls_set_gm(void) __attribute__((naked));
+void cgo_tls_get_gm(void) __attribute__((naked));
+void __aeabi_read_tp(void) {
+	// this function is only allowed to clobber r0
+	__asm__ __volatile__ (
+		"mrc p15, 0, r0, c13, c0, 3\n\t"
+		"cmp r0, #0\n\t"
+		"movne pc, lr\n\t"
+		"push {r1,r2,r3,r12}\n\t"
+		"svc 0x00a0013c\n\t" // _lwp_getprivate
+		"pop {r1,r2,r3,r12}\n\t"
+		"mov pc, lr\n\t"
+	);
+}
+// g (R10) at 8(TP), m (R9) at 12(TP)
+void cgo_tls_get_gm(void) {
+	__asm__ __volatile__ (
+		"push {lr}\n\t"
+		"bl __aeabi_read_tp\n\t"
+		"ldr r10, [r0, #8]\n\t"
+		"ldr r9, [r0, #12]\n\t"
+		"pop {pc}\n\t"
+	);
+}
+void cgo_tls_set_gm(void) {
+	__asm__ __volatile__ (
+		"push {lr}\n\t"
+		"bl __aeabi_read_tp\n\t"
+		"str r10, [r0, #8]\n\t"
+		"str r9, [r0, #12]\n\t"
+		"pop {pc}\n\t"
+	);
+}
+// both cgo_tls_{get,set}_gm can be called from runtime
+void (*cgo_load_gm)(void) = cgo_tls_get_gm;
+void (*cgo_save_gm)(void) = cgo_tls_set_gm;
+
+static void
+xinitcgo(G *g)
+{
+	pthread_attr_t attr;
+	size_t size;
+	cgo_tls_set_gm(); // save g and m for the initial thread
+
+	pthread_attr_init(&attr);
+	pthread_attr_getstacksize(&attr, &size);
+	g->stackguard = (uintptr)&attr - size + 4096;
+	pthread_attr_destroy(&attr);
+}
+
+void (*initcgo)(G*) = xinitcgo;
+
+void
+libcgo_sys_thread_start(ThreadStart *ts)
+{
+	pthread_attr_t attr;
+	sigset_t ign, oset;
+	pthread_t p;
+	size_t size;
+	int err;
+
+	sigfillset(&ign);
+	sigprocmask(SIG_SETMASK, &ign, &oset);
+
+	pthread_attr_init(&attr);
+	pthread_attr_getstacksize(&attr, &size);
+	ts->g->stackguard = size;
+	err = pthread_create(&p, &attr, threadentry, ts);
+
+	sigprocmask(SIG_SETMASK, &oset, nil);
+
+	if (err != 0) {
+		fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
+		abort();
+	}
+}
+
+extern void crosscall_arm2(void (*fn)(void), void *g, void *m);
+static void*
+threadentry(void *v)
+{
+	ThreadStart ts;
+
+	ts = *(ThreadStart*)v;
+	free(v);
+
+	ts.g->stackbase = (uintptr)&ts;
+
+	/*
+	 * libcgo_sys_thread_start set stackguard to stack size;
+	 * change to actual guard pointer.
+	 */
+	ts.g->stackguard = (uintptr)&ts - ts.g->stackguard + 4096 * 2;
+
+	crosscall_arm2(ts.fn, (void *)ts.g, (void *)ts.m);
+	return nil;
+}