cmd/dist,runtime: support cgo on openbsd/mips64

Add support for cgo on openbsd/mips64.

Fixes #43005

Change-Id: I2386204f53fa984a01a9d89f0b6c96455768f326
Reviewed-on: https://go-review.googlesource.com/c/go/+/275896
Trust: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/dist/build.go

@@ -1590,7 +1590,7 @@ var cgoEnabled = map[string]bool{
 	"openbsd/amd64":   true,
 	"openbsd/arm":     true,
 	"openbsd/arm64":   true,
-	"openbsd/mips64":  false,
+	"openbsd/mips64":  true,
 	"plan9/386":       false,
 	"plan9/amd64":     false,
 	"plan9/arm":       false,

src/cmd/link/internal/mips64/asm.go

@@ -52,6 +52,8 @@ func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym,
 	//		type	uint8
 	//		addend	int64
 
+	addend := r.Xadd
+
 	out.Write64(uint64(sectoff))
 
 	elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
@@ -77,11 +79,17 @@ func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym,
 		out.Write8(uint8(elf.R_MIPS_HI16))
 	case objabi.R_ADDRMIPSTLS:
 		out.Write8(uint8(elf.R_MIPS_TLS_TPREL_LO16))
+		if ctxt.Target.IsOpenbsd() {
+			// OpenBSD mips64 does not currently offset TLS by 0x7000,
+			// as such we need to add this back to get the correct offset
+			// via the external linker.
+			addend += 0x7000
+		}
 	case objabi.R_CALLMIPS,
 		objabi.R_JMPMIPS:
 		out.Write8(uint8(elf.R_MIPS_26))
 	}
-	out.Write64(uint64(r.Xadd))
+	out.Write64(uint64(addend))
 
 	return true
 }
@@ -124,6 +132,11 @@ func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loade
 	case objabi.R_ADDRMIPSTLS:
 		// thread pointer is at 0x7000 offset from the start of TLS data area
 		t := ldr.SymValue(rs) + r.Add() - 0x7000
+		if target.IsOpenbsd() {
+			// OpenBSD mips64 does not currently offset TLS by 0x7000,
+			// as such we need to add this back to get the correct offset.
+			t += 0x7000
+		}
 		if t < -32768 || t >= 32678 {
 			ldr.Errorf(s, "TLS offset out of range %d", t)
 		}

src/cmd/nm/nm_cgo_test.go

@@ -30,7 +30,7 @@ func canInternalLink() bool {
 		}
 	case "openbsd":
 		switch runtime.GOARCH {
-		case "arm64":
+		case "arm64", "mips64":
 			return false
 		}
 	case "windows":

src/runtime/cgo/gcc_openbsd_mips64.c

@@ -0,0 +1,67 @@
+// Copyright 2020 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"
+#include "libcgo_unix.h"
+
+static void* threadentry(void*);
+static void (*setg_gcc)(void*);
+
+void
+x_cgo_init(G *g, void (*setg)(void*))
+{
+	pthread_attr_t attr;
+	size_t size;
+
+	setg_gcc = setg;
+	pthread_attr_init(&attr);
+	pthread_attr_getstacksize(&attr, &size);
+	g->stacklo = (uintptr)&attr - size + 4096;
+	pthread_attr_destroy(&attr);
+}
+
+void
+_cgo_sys_thread_start(ThreadStart *ts)
+{
+	pthread_attr_t attr;
+	sigset_t ign, oset;
+	pthread_t p;
+	size_t size;
+	int err;
+
+	sigfillset(&ign);
+	pthread_sigmask(SIG_SETMASK, &ign, &oset);
+
+	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);
+
+	pthread_sigmask(SIG_SETMASK, &oset, nil);
+
+	if (err != 0) {
+		fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
+		abort();
+	}
+}
+
+extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
+
+static void*
+threadentry(void *v)
+{
+	ThreadStart ts;
+
+	ts = *(ThreadStart*)v;
+	free(v);
+
+	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
+	return nil;
+}