cmd/internal/obj, cmd/link: fix st_other field on PPC64

In PPC64 ELF files, the st_other field indicates the number of
prologue instructions between the global and local entry points.
We add the instructions in the compiler and assembler if -shared is used.
We were assuming that the instructions were present when building a
c-archive or PIE or doing dynamic linking, on the assumption that those
are the cases where the go tool would be building with -shared.
That assumption fails when using some other tool, such as Bazel,
that does not necessarily use -shared in exactly the same way.

This CL records in the object file whether a symbol was compiled
with -shared (this will be the same for all symbols in a given compilation)
and uses that information when setting the st_other field.

Fixes #20290.

Change-Id: Ib2b77e16aef38824871102e3c244fcf04a86c6ea
Reviewed-on: https://go-review.googlesource.com/43051
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

misc/cgo/testcarchive/carchive_test.go

@@ -218,15 +218,7 @@ func TestEarlySignalHandler(t *testing.T) {
 }
 
 func TestSignalForwarding(t *testing.T) {
-	switch GOOS {
-	case "darwin":
-		switch GOARCH {
-		case "arm", "arm64":
-			t.Skipf("skipping on %s/%s; see https://golang.org/issue/13701", GOOS, GOARCH)
-		}
-	case "windows":
-		t.Skip("skipping signal test on Windows")
-	}
+	checkSignalForwardingTest(t)
 
 	defer func() {
 		os.Remove("libgo2.a")
@@ -251,51 +243,19 @@ func TestSignalForwarding(t *testing.T) {
 	cmd = exec.Command(bin[0], append(bin[1:], "1")...)
 
 	out, err := cmd.CombinedOutput()
-
-	if err == nil {
-		t.Logf("%s", out)
-		t.Error("test program succeeded unexpectedly")
-	} else if ee, ok := err.(*exec.ExitError); !ok {
-		t.Logf("%s", out)
-		t.Errorf("error (%v) has type %T; expected exec.ExitError", err, err)
-	} else if ws, ok := ee.Sys().(syscall.WaitStatus); !ok {
-		t.Logf("%s", out)
-		t.Errorf("error.Sys (%v) has type %T; expected syscall.WaitStatus", ee.Sys(), ee.Sys())
-	} else if !ws.Signaled() || ws.Signal() != syscall.SIGSEGV {
-		t.Logf("%s", out)
-		t.Errorf("got %v; expected SIGSEGV", ee)
-	}
+	t.Logf("%s", out)
+	expectSignal(t, err, syscall.SIGSEGV)
 
 	// Test SIGPIPE forwarding
 	cmd = exec.Command(bin[0], append(bin[1:], "3")...)
 
 	out, err = cmd.CombinedOutput()
-
-	if err == nil {
-		t.Logf("%s", out)
-		t.Error("test program succeeded unexpectedly")
-	} else if ee, ok := err.(*exec.ExitError); !ok {
-		t.Logf("%s", out)
-		t.Errorf("error (%v) has type %T; expected exec.ExitError", err, err)
-	} else if ws, ok := ee.Sys().(syscall.WaitStatus); !ok {
-		t.Logf("%s", out)
-		t.Errorf("error.Sys (%v) has type %T; expected syscall.WaitStatus", ee.Sys(), ee.Sys())
-	} else if !ws.Signaled() || ws.Signal() != syscall.SIGPIPE {
-		t.Logf("%s", out)
-		t.Errorf("got %v; expected SIGPIPE", ee)
-	}
+	t.Logf("%s", out)
+	expectSignal(t, err, syscall.SIGPIPE)
 }
 
 func TestSignalForwardingExternal(t *testing.T) {
-	switch GOOS {
-	case "darwin":
-		switch GOARCH {
-		case "arm", "arm64":
-			t.Skipf("skipping on %s/%s; see https://golang.org/issue/13701", GOOS, GOARCH)
-		}
-	case "windows":
-		t.Skip("skipping signal test on Windows")
-	}
+	checkSignalForwardingTest(t)
 
 	defer func() {
 		os.Remove("libgo2.a")
@@ -363,14 +323,7 @@ func TestSignalForwardingExternal(t *testing.T) {
 			continue
 		}
 
-		if ee, ok := err.(*exec.ExitError); !ok {
-			t.Errorf("error (%v) has type %T; expected exec.ExitError", err, err)
-		} else if ws, ok := ee.Sys().(syscall.WaitStatus); !ok {
-			t.Errorf("error.Sys (%v) has type %T; expected syscall.WaitStatus", ee.Sys(), ee.Sys())
-		} else if !ws.Signaled() || ws.Signal() != syscall.SIGSEGV {
-			t.Errorf("got %v; expected SIGSEGV", ee)
-		} else {
-			// We got the error we expected.
+		if expectSignal(t, err, syscall.SIGSEGV) {
 			return
 		}
 	}
@@ -378,6 +331,38 @@ func TestSignalForwardingExternal(t *testing.T) {
 	t.Errorf("program succeeded unexpectedly %d times", tries)
 }
 
+// checkSignalForwardingTest calls t.Skip if the SignalForwarding test
+// doesn't work on this platform.
+func checkSignalForwardingTest(t *testing.T) {
+	switch GOOS {
+	case "darwin":
+		switch GOARCH {
+		case "arm", "arm64":
+			t.Skipf("skipping on %s/%s; see https://golang.org/issue/13701", GOOS, GOARCH)
+		}
+	case "windows":
+		t.Skip("skipping signal test on Windows")
+	}
+}
+
+// expectSignal checks that err, the exit status of a test program,
+// shows a failure due to a specific signal. Returns whether we found
+// the expected signal.
+func expectSignal(t *testing.T, err error, sig syscall.Signal) bool {
+	if err == nil {
+		t.Error("test program succeeded unexpectedly")
+	} else if ee, ok := err.(*exec.ExitError); !ok {
+		t.Errorf("error (%v) has type %T; expected exec.ExitError", err, err)
+	} else if ws, ok := ee.Sys().(syscall.WaitStatus); !ok {
+		t.Errorf("error.Sys (%v) has type %T; expected syscall.WaitStatus", ee.Sys(), ee.Sys())
+	} else if !ws.Signaled() || ws.Signal() != sig {
+		t.Errorf("got %v; expected signal %v", ee, sig)
+	} else {
+		return true
+	}
+	return false
+}
+
 func TestOsSignal(t *testing.T) {
 	switch GOOS {
 	case "windows":
@@ -592,3 +577,44 @@ func TestSIGPROF(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+// TestCompileWithoutShared tests that if we compile code without the
+// -shared option, we can put it into an archive. When we use the go
+// tool with -buildmode=c-archive, it passes -shared to the compiler,
+// so we override that. The go tool doesn't work this way, but Bazel
+// will likely do it in the future. And it ought to work. This test
+// was added because at one time it did not work on PPC GNU/Linux.
+func TestCompileWithoutShared(t *testing.T) {
+	// For simplicity, reuse the signal forwarding test.
+	checkSignalForwardingTest(t)
+
+	defer func() {
+		os.Remove("libgo2.a")
+		os.Remove("libgo2.h")
+	}()
+
+	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-gcflags=-shared=false", "-o", "libgo2.a", "libgo2")
+	cmd.Env = gopathEnv
+	t.Log(cmd.Args)
+	out, err := cmd.CombinedOutput()
+	t.Logf("%s", out)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	exe := "./testnoshared" + exeSuffix
+	ccArgs := append(cc, "-o", exe, "main5.c", "libgo2.a")
+	t.Log(ccArgs)
+	out, err = exec.Command(ccArgs[0], ccArgs[1:]...).CombinedOutput()
+	t.Logf("%s", out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(exe)
+
+	binArgs := append(cmdToRun(exe), "3")
+	t.Log(binArgs)
+	out, err = exec.Command(binArgs[0], binArgs[1:]...).CombinedOutput()
+	t.Logf("%s", out)
+	expectSignal(t, err, syscall.SIGPIPE)
+}

src/cmd/internal/goobj/read.go

@@ -532,7 +532,7 @@ func (r *objReader) parseObject(prefix []byte) error {
 			f.Args = r.readInt()
 			f.Frame = r.readInt()
 			flags := r.readInt()
-			f.Leaf = flags&1 != 0
+			f.Leaf = flags&(1<<0) != 0
 			f.NoSplit = r.readInt() != 0
 			f.Var = make([]Var, r.readInt())
 			for i := range f.Var {

src/cmd/internal/obj/objfile.go

@@ -338,6 +338,9 @@ func (w *objWriter) writeSym(s *LSym) {
 	if s.ReflectMethod() {
 		flags |= 1 << 2
 	}
+	if ctxt.Flag_shared {
+		flags |= 1 << 3
+	}
 	w.writeInt(flags)
 	w.writeInt(int64(len(s.Func.Autom)))
 	for _, a := range s.Func.Autom {

src/cmd/internal/obj/ppc64/obj9.go

@@ -476,6 +476,11 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				// generate the addis instruction except as part of the
 				// load of a large constant, and in that case there is no
 				// way to use r12 as the source.
+				//
+				// Note that the same condition is tested in
+				// putelfsym in cmd/link/internal/ld/symtab.go
+				// where we set the st_other field to indicate
+				// the presence of these instructions.
 				q = obj.Appendp(q, c.newprog)
 				q.As = AWORD
 				q.Pos = p.Pos

src/cmd/internal/objabi/doc.go

@@ -77,6 +77,7 @@
 //		1<<0 leaf
 //		1<<1 C function
 //		1<<2 function may call reflect.Type.Method
+//		1<<3 function compiled with -shared
 //	- nlocal [int]
 //	- local [nlocal automatics]
 //	- pcln [pcln table]

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

@@ -135,6 +135,9 @@ const (
 	// AttrMakeTypelink Amarks types that should be added to the typelink
 	// table. See typelinks.go:typelinks().
 	AttrMakeTypelink
+	// AttrShared marks symbols compiled with the -shared option.
+	AttrShared
+	// 14 attributes defined so far.
 )
 
 func (a Attribute) DuplicateOK() bool      { return a&AttrDuplicateOK != 0 }
@@ -150,6 +153,7 @@ func (a Attribute) OnList() bool           { return a&AttrOnList != 0 }
 func (a Attribute) Local() bool            { return a&AttrLocal != 0 }
 func (a Attribute) ReflectMethod() bool    { return a&AttrReflectMethod != 0 }
 func (a Attribute) MakeTypelink() bool     { return a&AttrMakeTypelink != 0 }
+func (a Attribute) Shared() bool           { return a&AttrShared != 0 }
 
 func (a Attribute) CgoExport() bool {
 	return a.CgoExportDynamic() || a.CgoExportStatic()

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

@@ -258,6 +258,9 @@ overwrite:
 		if flags&(1<<2) != 0 {
 			s.Attr |= AttrReflectMethod
 		}
+		if flags&(1<<3) != 0 {
+			s.Attr |= AttrShared
+		}
 		n := r.readInt()
 		pc.Autom = r.autom[:n:n]
 		if !isdup {

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

@@ -147,10 +147,13 @@ func putelfsym(ctxt *Link, x *Symbol, s string, t SymbolType, addr int64, go_ *S
 	if x.Type&SHIDDEN != 0 {
 		other = STV_HIDDEN
 	}
-	if (Buildmode == BuildmodeCArchive || Buildmode == BuildmodePIE || ctxt.DynlinkingGo()) && SysArch.Family == sys.PPC64 && typ == STT_FUNC && x.Name != "runtime.duffzero" && x.Name != "runtime.duffcopy" {
+	if SysArch.Family == sys.PPC64 && typ == STT_FUNC && x.Attr.Shared() && x.Name != "runtime.duffzero" && x.Name != "runtime.duffcopy" {
 		// On ppc64 the top three bits of the st_other field indicate how
 		// many instructions separate the global and local entry points. In
 		// our case it is two instructions, indicated by the value 3.
+		// The conditions here match those in preprocess in
+		// cmd/internal/obj/ppc64/obj9.go, which is where the
+		// instructions are inserted.
 		other |= 3 << 5
 	}