cmd/link: enable -buildmode=plugin for ppc64le

This enables support for the buildmode plugin on
ppc64le.

Fixes #20756

Change-Id: I83241ff63f9b5c366fe0496cf46a3f67d75d08ac
Reviewed-on: https://go-review.googlesource.com/55850
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/dist/test.go

@@ -840,7 +840,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		// linux-arm64 is missing because it causes the external linker
 		// to crash, see https://golang.org/issue/17138
 		switch pair {
-		case "linux-386", "linux-amd64", "linux-arm", "linux-s390x":
+		case "linux-386", "linux-amd64", "linux-arm", "linux-s390x", "linux-ppc64le":
 			return true
 		case "darwin-amd64":
 			return true

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

@@ -356,7 +356,7 @@ func BuildModeInit() {
 			codegenArg = "-fPIC"
 		} else {
 			switch platform {
-			case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/s390x",
+			case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/s390x", "linux/ppc64le",
 				"android/amd64", "android/arm", "android/arm64", "android/386":
 			case "darwin/amd64":
 				// Skip DWARF generation due to #21647

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

@@ -90,7 +90,7 @@ func (mode *BuildMode) Set(s string) error {
 		switch objabi.GOOS {
 		case "linux":
 			switch objabi.GOARCH {
-			case "386", "amd64", "arm", "arm64", "s390x":
+			case "386", "amd64", "arm", "arm64", "s390x", "ppc64le":
 			default:
 				return badmode()
 			}

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

@@ -168,8 +168,12 @@ func (ctxt *Link) DynlinkingGo() bool {
 	if !ctxt.Loaded {
 		panic("DynlinkingGo called before all symbols loaded")
 	}
-	canUsePlugins := ctxt.Syms.ROLookup("plugin.Open", 0) != nil
+	return Buildmode == BuildmodeShared || *FlagLinkshared || Buildmode == BuildmodePlugin || ctxt.CanUsePlugins()
-	return Buildmode == BuildmodeShared || *FlagLinkshared || Buildmode == BuildmodePlugin || canUsePlugins
+}
+
+// CanUsePlugins returns whether a plugins can be used
+func (ctxt *Link) CanUsePlugins() bool {
+	return ctxt.Syms.ROLookup("plugin.Open", 0) != nil
 }
 
 // UseRelro returns whether to make use of "read only relocations" aka

src/cmd/link/internal/ppc64/asm.go

@@ -131,7 +131,7 @@ func genplt(ctxt *ld.Link) {
 
 func genaddmoduledata(ctxt *ld.Link) {
 	addmoduledata := ctxt.Syms.ROLookup("runtime.addmoduledata", 0)
-	if addmoduledata.Type == ld.STEXT {
+	if addmoduledata.Type == ld.STEXT && ld.Buildmode != ld.BuildmodePlugin {
 		return
 	}
 	addmoduledata.Attr |= ld.AttrReachable
@@ -147,6 +147,7 @@ func genaddmoduledata(ctxt *ld.Link) {
 	rel.Off = int32(initfunc.Size)
 	rel.Siz = 8
 	rel.Sym = ctxt.Syms.Lookup(".TOC.", 0)
+	rel.Sym.Attr |= ld.AttrReachable
 	rel.Type = objabi.R_ADDRPOWER_PCREL
 	o(0x3c4c0000)
 	// addi r2, r2, .TOC.-func@l
@@ -159,7 +160,13 @@ func genaddmoduledata(ctxt *ld.Link) {
 	rel = ld.Addrel(initfunc)
 	rel.Off = int32(initfunc.Size)
 	rel.Siz = 8
-	rel.Sym = ctxt.Syms.Lookup("local.moduledata", 0)
+	if !ctxt.CanUsePlugins() {
+		rel.Sym = ctxt.Syms.Lookup("local.moduledata", 0)
+	} else {
+		rel.Sym = ctxt.Syms.Lookup("runtime.firstmoduledata", 0)
+	}
+	rel.Sym.Attr |= ld.AttrReachable
+	rel.Sym.Attr |= ld.AttrLocal
 	rel.Type = objabi.R_ADDRPOWER_GOT
 	o(0x3c620000)
 	// ld r3, local.moduledata@got@l(r3)
@@ -182,6 +189,9 @@ func genaddmoduledata(ctxt *ld.Link) {
 	// blr
 	o(0x4e800020)
 
+	if ld.Buildmode == ld.BuildmodePlugin {
+		ctxt.Textp = append(ctxt.Textp, addmoduledata)
+	}
 	initarray_entry := ctxt.Syms.Lookup("go.link.addmoduledatainit", 0)
 	ctxt.Textp = append(ctxt.Textp, initfunc)
 	initarray_entry.Attr |= ld.AttrReachable