cmd/compile,cmd/internal/objabi: abstract out object header string

Change-Id: Idbbb4cb7127b93afa34a8aa18bbdaad1f206ab6a
Reviewed-on: https://go-review.googlesource.com/c/go/+/308090
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

3 files changed, 13 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/gc/obj.go b/src/cmd/compile/internal/gc/obj.go
index d18011a9e5..f87a3c6b48 100644
--- a/src/cmd/compile/internal/gc/obj.go
+++ b/src/cmd/compile/internal/gc/obj.go
@@ -70,7 +70,7 @@ func dumpobj1(outfile string, mode int) {
 }
 
 func printObjHeader(bout *bio.Writer) {
-	fmt.Fprintf(bout, "go object %s %s %s %s\n", objabi.GOOS, objabi.GOARCH, objabi.Version, objabi.Expstring())
+	bout.WriteString(objabi.HeaderString())
 	if base.Flag.BuildID != "" {
 		fmt.Fprintf(bout, "build id %q\n", base.Flag.BuildID)
 	}
diff --git a/src/cmd/compile/internal/noder/import.go b/src/cmd/compile/internal/noder/import.go
index 89a2598833..e6e3fe1834 100644
--- a/src/cmd/compile/internal/noder/import.go
+++ b/src/cmd/compile/internal/noder/import.go
@@ -243,9 +243,9 @@ func importfile(decl *syntax.ImportDecl) *types.Pkg {
 		base.Errorf("import %s: not a go object file: %s", file, p)
 		base.ErrorExit()
 	}
-	q := fmt.Sprintf("%s %s %s %s\n", objabi.GOOS, objabi.GOARCH, objabi.Version, objabi.Expstring())
-	if p[10:] != q {
-		base.Errorf("import %s: object is [%s] expected [%s]", file, p[10:], q)
+	q := objabi.HeaderString()
+	if p != q {
+		base.Errorf("import %s: object is [%s] expected [%s]", file, p, q)
 		base.ErrorExit()
 	}
 
diff --git a/src/cmd/internal/objabi/util.go b/src/cmd/internal/objabi/util.go
index 76c56dab27..c2c05bd1b2 100644
--- a/src/cmd/internal/objabi/util.go
+++ b/src/cmd/internal/objabi/util.go
@@ -5,6 +5,7 @@
 package objabi
 
 import (
+	"fmt"
 	"log"
 	"os"
 	"strings"
@@ -121,3 +122,11 @@ func gowasm() (f gowasmFeatures) {
 func Getgoextlinkenabled() string {
 	return envOr("GO_EXTLINK_ENABLED", defaultGO_EXTLINK_ENABLED)
 }
+
+// HeaderString returns the toolchain configuration string written in
+// Go object headers. This string ensures we don't attempt to import
+// or link object files that are incompatible with each other. This
+// string always starts with "go object ".
+func HeaderString() string {
+	return fmt.Sprintf("go object %s %s %s %s\n", GOOS, GOARCH, Version, Expstring())
+}