code review 7432048: cmd/cgo: use explicit flag to emit dynamic linker path

src/cmd/go/build.go

 // Copyright 2011 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package main
 
 import (
         "bytes"
         "container/heap"
         "errors"
@@ skipping 1846 matching lines @@
                 cgoLDFLAGS = cgoLDFLAGS[0 : len(cgoLDFLAGS)-1]
         }
 
         if _, ok := buildToolchain.(gccgoToolchain); ok {
                 // we don't use dynimport when using gccgo.
                 return outGo, outObj, nil
         }
 
         // cgo -dynimport
         importC := obj + "_cgo_import.c"
-        if err := b.run(p.Dir, p.ImportPath, cgoExe, "-objdir", obj, "-dynimport", dynobj, "-dynout", importC); err != nil {
+        cgoflags = []string{}
+        if p.Standard && p.ImportPath == "runtime/cgo" {
+                cgoflags = append(cgoflags, "-dynlinker") // record path to dynamic linker
+        }
+        if err := b.run(p.Dir, p.ImportPath, cgoExe, "-objdir", obj, "-dynimport", dynobj, "-dynout", importC, cgoflags); err != nil {
                 return nil, nil, err
         }
 
         // cc _cgo_import.ARCH
         importObj := obj + "_cgo_import." + objExt
         if err := buildToolchain.cc(b, p, obj, importObj, importC); err != nil {
                 return nil, nil, err
         }
 
         ofile := obj + "_all.o"
@@ skipping 145 matching lines @@
         if goarch != "amd64" || goos != "linux" && goos != "darwin" && goos != "windows" {
                 fmt.Fprintf(os.Stderr, "go %s: -race is only supported on linux/amd64, darwin/amd64 and windows/amd64\n", flag.Args()[0])
                 os.Exit(2)
         }
         buildGcflags = append(buildGcflags, "-race")
         buildLdflags = append(buildLdflags, "-race")
         buildCcflags = append(buildCcflags, "-D", "RACE")
         buildContext.InstallTag = "race"
         buildContext.BuildTags = append(buildContext.BuildTags, "race")
 }