[dev.cc] cmd/asm: the assembler proper

Add main.go, the simple driver for the assembler, and the
subdirectory internal/asm, which contains the parser and
instruction generator.

It's likely that much of the implementation is superstition,
or at best experimental phenomenology, but it does generate
working binaries.

Change-Id: I322a9ae8a20174b6693153f30e39217ba68f8032
Reviewed-on: https://go-review.googlesource.com/3196
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/asm/main.go

@@ -0,0 +1,63 @@
+// Copyright 2014 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 (
+	"flag"
+	"fmt"
+	"go/build"
+	"log"
+	"os"
+
+	"cmd/asm/internal/arch"
+	"cmd/asm/internal/asm"
+	"cmd/asm/internal/flags"
+	"cmd/asm/internal/lex"
+
+	"cmd/internal/obj"
+)
+
+func main() {
+	log.SetFlags(0)
+	log.SetPrefix("asm: ")
+
+	GOARCH := build.Default.GOARCH
+
+	architecture := arch.Set(GOARCH)
+	if architecture == nil {
+		log.Fatalf("asm: unrecognized architecture %s", GOARCH)
+	}
+
+	// Is this right?
+	flags.Parse(build.Default.GOROOT, build.Default.GOOS, GOARCH, architecture.Thechar)
+
+	// Create object file, write header.
+	fd, err := os.Create(*flags.OutputFile)
+	if err != nil {
+		log.Fatal(err)
+	}
+	ctxt := obj.Linknew(architecture.LinkArch)
+	if *flags.PrintOut {
+		ctxt.Debugasm = 1
+	}
+	ctxt.Bso = obj.Binitw(os.Stdout)
+	defer obj.Bflush(ctxt.Bso)
+	ctxt.Diag = log.Fatalf
+	output := obj.Binitw(fd)
+	fmt.Fprintf(output, "go object %s %s %s\n", obj.Getgoos(), obj.Getgoarch(), obj.Getgoversion())
+	fmt.Fprintf(output, "!\n")
+
+	lexer := lex.NewLexer(flag.Arg(0), ctxt)
+	parser := asm.NewParser(ctxt, architecture, lexer)
+	pList := obj.Linknewplist(ctxt)
+	var ok bool
+	pList.Firstpc, ok = parser.Parse()
+	if !ok {
+		log.Print("FAIL TODO")
+		os.Exit(1)
+	}
+	obj.Writeobjdirect(ctxt, output)
+	obj.Bflush(output)
+}