cmd/asm, cmd/link: use full objabi header

The cmd/link check of the objabi header was a bit lax because
historically the assembler has not included the full version string.
And the assembler didn't do that because it didn't have access to it:
that was buried inside the compiler.

But now that we have cmd/internal/objabi, all the tools have full
access to the expected string, and they can use it, which simplifies
the cmd/link consistency check.

Do that.

Change-Id: I33bd2f9d36c373cc3c32ff02ec6368365088b011
Reviewed-on: https://go-review.googlesource.com/c/go/+/312030
Trust: Russ Cox <[email protected]>
Run-TryBot: Russ Cox <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

src/cmd/asm/main.go

@@ -19,6 +19,7 @@ import (
 
 	"cmd/internal/bio"
 	"cmd/internal/obj"
+	"cmd/internal/objabi"
 )
 
 func main() {
@@ -69,7 +70,7 @@ func main() {
 	defer buf.Close()
 
 	if !*flags.SymABIs {
-		fmt.Fprintf(buf, "go object %s %s %s\n", buildcfg.GOOS, buildcfg.GOARCH, buildcfg.Version)
+		buf.WriteString(objabi.HeaderString())
 		fmt.Fprintf(buf, "!\n")
 	}
 

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

@@ -1773,6 +1773,8 @@ func hostlinkArchArgs(arch *sys.Arch) []string {
 	return nil
 }
 
+var wantHdr = objabi.HeaderString()
+
 // ldobj loads an input object. If it is a host object (an object
 // compiled by a non-Go compiler) it returns the Hostobj pointer. If
 // it is a Go object, it returns nil.
@@ -1871,24 +1873,8 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 	}
 
 	// First, check that the basic GOOS, GOARCH, and Version match.
-	t := fmt.Sprintf("%s %s %s ", buildcfg.GOOS, buildcfg.GOARCH, buildcfg.Version)
-
-	line = strings.TrimRight(line, "\n")
-	if !strings.HasPrefix(line[10:]+" ", t) && !*flagF {
-		Errorf(nil, "%s: object is [%s] expected [%s]", pn, line[10:], t)
-		return nil
-	}
-
-	// Second, check that longer lines match each other exactly,
-	// so that the Go compiler and write additional information
-	// that must be the same from run to run.
-	if len(line) >= len(t)+10 {
-		if theline == "" {
-			theline = line[10:]
-		} else if theline != line[10:] {
-			Errorf(nil, "%s: object is [%s] expected [%s]", pn, line[10:], theline)
-			return nil
-		}
+	if line != wantHdr {
+		Errorf(nil, "%s: linked object header mismatch:\nhave %q\nwant %q\n", pn, line, wantHdr)
 	}
 
 	// Skip over exports and other info -- ends with \n!\n.