cmd/cgo: permit missing dynamic symbol section

Allow static complication of cgo enabled libraries.

Fixes #16651

Change-Id: I0729ee4e6e5f9bd1cbdb1bc2dcbfe34463df547c
Reviewed-on: https://go-review.googlesource.com/89655
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/test/issue4029.c

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !windows
+// +build !windows,!static
 
 #include <stdint.h>
 #include <dlfcn.h>

misc/cgo/test/issue4029.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !windows
+// +build !windows,!static
 
 package cgotest
 

misc/cgo/test/issue4029w.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build windows
+// +build windows static
 
 package cgotest
 

src/cmd/cgo/out.go

@@ -272,10 +272,7 @@ func dynimport(obj string) {
 				}
 			}
 		}
-		sym, err := f.ImportedSymbols()
-		if err != nil {
-			fatalf("cannot load imported symbols from ELF file %s: %v", obj, err)
-		}
+		sym, _ := f.ImportedSymbols()
 		for _, s := range sym {
 			targ := s.Name
 			if s.Version != "" {
@@ -283,10 +280,7 @@ func dynimport(obj string) {
 			}
 			fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s.Name, targ, s.Library)
 		}
-		lib, err := f.ImportedLibraries()
-		if err != nil {
-			fatalf("cannot load imported libraries from ELF file %s: %v", obj, err)
-		}
+		lib, _ := f.ImportedLibraries()
 		for _, l := range lib {
 			fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
 		}
@@ -294,20 +288,14 @@ func dynimport(obj string) {
 	}
 
 	if f, err := macho.Open(obj); err == nil {
-		sym, err := f.ImportedSymbols()
-		if err != nil {
-			fatalf("cannot load imported symbols from Mach-O file %s: %v", obj, err)
-		}
+		sym, _ := f.ImportedSymbols()
 		for _, s := range sym {
 			if len(s) > 0 && s[0] == '_' {
 				s = s[1:]
 			}
 			fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s, s, "")
 		}
-		lib, err := f.ImportedLibraries()
-		if err != nil {
-			fatalf("cannot load imported libraries from Mach-O file %s: %v", obj, err)
-		}
+		lib, _ := f.ImportedLibraries()
 		for _, l := range lib {
 			fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
 		}
@@ -315,10 +303,7 @@ func dynimport(obj string) {
 	}
 
 	if f, err := pe.Open(obj); err == nil {
-		sym, err := f.ImportedSymbols()
-		if err != nil {
-			fatalf("cannot load imported symbols from PE file %s: %v", obj, err)
-		}
+		sym, _ := f.ImportedSymbols()
 		for _, s := range sym {
 			ss := strings.Split(s, ":")
 			name := strings.Split(ss[0], "@")[0]

src/cmd/dist/test.go

@@ -1065,6 +1065,12 @@ func (t *tester) cgoTest(dt *distTest) error {
 				t.addCmd(dt, "misc/cgo/nocgo", t.goTest(), "-ldflags", `-linkmode=external`)
 				if goos != "android" {
 					t.addCmd(dt, "misc/cgo/nocgo", t.goTest(), "-ldflags", `-linkmode=external -extldflags "-static -pthread"`)
+					t.addCmd(dt, "misc/cgo/test", t.goTest(), "-tags=static", "-ldflags", `-linkmode=external -extldflags "-static -pthread"`)
+					// -static in CGO_LDFLAGS triggers a different code path
+					// than -static in -extldflags, so test both.
+					// See issue #16651.
+					cmd := t.addCmd(dt, "misc/cgo/test", t.goTest(), "-tags=static")
+					cmd.Env = append(os.Environ(), "CGO_LDFLAGS=-static -pthread")
 				}
 			}