cmd/link: detect -X setting non-string variable

Fixes #9621.

Change-Id: Ib9c6001378364af899f57fd4b89fb23af2042923
Reviewed-on: https://go-review.googlesource.com/11694
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

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

@@ -917,6 +917,8 @@ func strnput(s string, n int) {
 	}
 }
 
+var strdata []*LSym
+
 func addstrdata1(arg string) {
 	i := strings.Index(arg, "=")
 	if i < 0 {
@@ -944,9 +946,21 @@ func addstrdata(name string, value string) {
 	// we know before entering this function.
 	s.Reachable = reachable
 
+	strdata = append(strdata, s)
+
 	sp.Reachable = reachable
 }
 
+func checkstrdata() {
+	for _, s := range strdata {
+		if s.Type == obj.STEXT {
+			Diag("cannot use -X with text symbol %s", s.Name)
+		} else if s.Gotype != nil && s.Gotype.Name != "type.string" {
+			Diag("cannot use -X with non-string symbol %s", s.Name)
+		}
+	}
+}
+
 func Addstring(s *LSym, str string) int64 {
 	if s.Type == 0 {
 		s.Type = obj.SNOPTRDATA

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

@@ -220,6 +220,7 @@ func Ldmain() {
 	}
 
 	checkgo()
+	checkstrdata()
 	deadcode()
 	callgraph()
 

test/linkx.go

@@ -14,6 +14,9 @@ import "fmt"
 var tbd string
 var overwrite string = "dibs"
 
+var b bool
+var x int
+
 func main() {
 	fmt.Println(tbd)
 	fmt.Println(overwrite)

test/linkx_run.go

@@ -14,6 +14,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"strings"
 )
 
 func main() {
@@ -49,4 +50,21 @@ func test(sep string) {
 		fmt.Println("-X linker flag should not accept keys without values")
 		os.Exit(1)
 	}
+
+	// Issue 9621
+	cmd = exec.Command("go", "run", "-ldflags=-X main.b=false -X main.x=42", "linkx.go")
+	outx, err := cmd.CombinedOutput()
+	if err == nil {
+		fmt.Println("-X linker flag should not overwrite non-strings")
+		os.Exit(1)
+	}
+	outstr := string(outx)
+	if !strings.Contains(outstr, "main.b") {
+		fmt.Printf("-X linker flag did not diagnose overwrite of main.b\n")
+		os.Exit(1)
+	}
+	if !strings.Contains(outstr, "main.x") {
+		fmt.Printf("-X linker flag did not diagnose overwrite of main.x\n")
+		os.Exit(1)
+	}
 }