cmd: merge branch 'dev.link' into master

In the dev.link branch we implemented the new object file format
and (part of) the linker improvements described in
https://golang.org/s/better-linker

The new object file is index-based and provides random access.
The linker maps the object files into read-only memory, and
access symbols on-demand using indices, as opposed to reading
all object files sequentially into the heap with the old format.

The linker carries symbol informations using indices (as opposed
to Symbol data structure). Symbols are created after the
reachability analysis, and only created for reachable symbols.
This reduces the linker's memory usage.

Linking cmd/compile, it creates ~25% fewer Symbols, and reduces
memory usage (inuse_space) by ~15%. (More results from Than.)

Currently, both the old and new object file formats are supported.
The old format is used by default. The new format can be turned
on by using the compiler/assembler/linker's -newobj flag. Note
that the flag needs to be specified consistently to all
compilations, i.e.

go build -gcflags=all=-newobj -asmflags=all=-newobj -ldflags=-newobj

Change-Id: Ia0e35306b5b9b5b19fdc7fa7c602d4ce36fa6abd

2 files changed, 6 insertions, 5 deletions

diff --git a/src/cmd/asm/internal/flags/flags.go b/src/cmd/asm/internal/flags/flags.go
index 5fe3fd9d53..fad87b221a 100644
--- a/src/cmd/asm/internal/flags/flags.go
+++ b/src/cmd/asm/internal/flags/flags.go
@@ -23,6 +23,7 @@ var (
 	Dynlink    = flag.Bool("dynlink", false, "support references to Go symbols defined in other shared libraries")
 	AllErrors  = flag.Bool("e", false, "no limit on number of errors reported")
 	SymABIs    = flag.Bool("gensymabis", false, "write symbol ABI information to output file, don't assemble")
+	Newobj     = flag.Bool("newobj", false, "use new object file format")
 )
 
 var (
diff --git a/src/cmd/asm/main.go b/src/cmd/asm/main.go
index fc6acc74c0..6b0a609071 100644
--- a/src/cmd/asm/main.go
+++ b/src/cmd/asm/main.go
@@ -40,18 +40,18 @@ func main() {
 	}
 	ctxt.Flag_dynlink = *flags.Dynlink
 	ctxt.Flag_shared = *flags.Shared || *flags.Dynlink
+	ctxt.Flag_newobj = *flags.Newobj
 	ctxt.Bso = bufio.NewWriter(os.Stdout)
 	defer ctxt.Bso.Flush()
 
 	architecture.Init(ctxt)
 
 	// Create object file, write header.
-	out, err := os.Create(*flags.OutputFile)
+	buf, err := bio.Create(*flags.OutputFile)
 	if err != nil {
 		log.Fatal(err)
 	}
-	defer bio.MustClose(out)
-	buf := bufio.NewWriter(bio.MustWriter(out))
+	defer buf.Close()
 
 	if !*flags.SymABIs {
 		fmt.Fprintf(buf, "go object %s %s %s\n", objabi.GOOS, objabi.GOARCH, objabi.Version)
@@ -83,6 +83,7 @@ func main() {
 		}
 	}
 	if ok && !*flags.SymABIs {
+		ctxt.NumberSyms(true)
 		obj.WriteObjFile(ctxt, buf, "")
 	}
 	if !ok || diag {
@@ -91,9 +92,8 @@ func main() {
 		} else {
 			log.Print("assembly failed")
 		}
-		out.Close()
+		buf.Close()
 		os.Remove(*flags.OutputFile)
 		os.Exit(1)
 	}
-	buf.Flush()
 }