cmd/go, cmd/link, cmd/dist: re-enable plugin mode on darwin/amd64

1. remove broken verification
   The runtime check assumes that no-pcln symbol entry have zero value,
   but the linker emit no entries if the symbol is no-pcln.
   As a result, if there are no-pcln symbols at the very end of pcln
   table, it will panic.
2. correct condition of export
   Handle special chracters in pluginpath correcty.
   Export "go.itab.*", so different plugins can share the same itab.

Fixes #18190

Change-Id: Ia4f9c51d83ce8488a9470520f1ee9432802cfc1d
Reviewed-on: https://go-review.googlesource.com/61091Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/cgo/testplugin/test.bash

@@ -40,11 +40,21 @@ GOPATH=$(pwd) go build -buildmode=plugin iface_b
 GOPATH=$(pwd) go build iface
 LD_LIBRARY_PATH=$(pwd) ./iface
 
+function _timeout() (
+	set -e
+	$2 &
+	p=$!
+	(sleep $1; kill $p 2>/dev/null) &
+	p2=$!
+	wait $p 2>/dev/null
+	kill -0 $p2 2>/dev/null
+)
+
 # Test for issue 18676 - make sure we don't add the same itab twice.
 # The buggy code hangs forever, so use a timeout to check for that.
 GOPATH=$(pwd) go build -buildmode=plugin -o plugin.so src/issue18676/plugin.go
 GOPATH=$(pwd) go build -o issue18676 src/issue18676/main.go
-timeout 10s ./issue18676
+_timeout 10 ./issue18676
 
 # Test for issue 19534 - that we can load a plugin built in a path with non-alpha
 # characters

src/cmd/dist/test.go

@@ -850,6 +850,8 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		switch pair {
 		case "linux-386", "linux-amd64", "linux-arm", "linux-s390x":
 			return true
+		case "darwin-amd64":
+			return true
 		}
 		return false
 	default:

src/cmd/go/internal/work/build.go

@@ -358,6 +358,9 @@ func BuildModeInit() {
 			switch platform {
 			case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/s390x",
 				"android/amd64", "android/arm", "android/arm64", "android/386":
+			case "darwin/amd64":
+				// Skip DWARF generation due to #21647
+				cfg.BuildLdflags = append(cfg.BuildLdflags, "-w")
 			default:
 				base.Fatalf("-buildmode=plugin not supported on %s\n", platform)
 			}

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

@@ -5,6 +5,7 @@
 package ld
 
 import (
+	"cmd/internal/objabi"
 	"cmd/internal/sys"
 	"sort"
 	"strings"
@@ -746,7 +747,10 @@ func machoShouldExport(ctxt *Link, s *Symbol) bool {
 	if !ctxt.DynlinkingGo() || s.Attr.Local() {
 		return false
 	}
-	if Buildmode == BuildmodePlugin && strings.HasPrefix(s.Extname, *flagPluginPath) {
+	if Buildmode == BuildmodePlugin && strings.HasPrefix(s.Extname, objabi.PathToPrefix(*flagPluginPath)) {
+		return true
+	}
+	if strings.HasPrefix(s.Name, "go.itab.") {
 		return true
 	}
 	if strings.HasPrefix(s.Name, "type.") && !strings.HasPrefix(s.Name, "type..") {

src/runtime/symtab.go

@@ -526,7 +526,6 @@ func moduledataverify1(datap *moduledata) {
 
 	// ftab is lookup table for function by program counter.
 	nftab := len(datap.ftab) - 1
-	var pcCache pcvalueCache
 	for i := 0; i < nftab; i++ {
 		// NOTE: ftab[nftab].entry is legal; it is the address beyond the final function.
 		if datap.ftab[i].entry > datap.ftab[i+1].entry {
@@ -542,30 +541,6 @@ func moduledataverify1(datap *moduledata) {
 			}
 			throw("invalid runtime symbol table")
 		}
-
-		if debugPcln || nftab-i < 5 {
-			// Check a PC near but not at the very end.
-			// The very end might be just padding that is not covered by the tables.
-			// No architecture rounds function entries to more than 16 bytes,
-			// but if one came along we'd need to subtract more here.
-			// But don't use the next PC if it corresponds to a foreign object chunk
-			// (no pcln table, f2.pcln == 0). That chunk might have an alignment
-			// more than 16 bytes.
-			f := funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i].funcoff])), datap}
-			end := f.entry
-			if i+1 < nftab {
-				f2 := funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i+1].funcoff])), datap}
-				if f2.pcln != 0 {
-					end = f2.entry - 16
-					if end < f.entry {
-						end = f.entry
-					}
-				}
-			}
-			pcvalue(f, f.pcfile, end, &pcCache, true)
-			pcvalue(f, f.pcln, end, &pcCache, true)
-			pcvalue(f, f.pcsp, end, &pcCache, true)
-		}
 	}
 
 	if datap.minpc != datap.ftab[0].entry ||