Add COM cmd to load MS-DOS COM files

Since COM files don't have a header/magic, has a simple memory map, it's
best to have it a separate command.

.gitignore

@@ -1,6 +1,7 @@
 deps/
 
 /cgc
+/com
 /fuzz
 /imgtrace
 /repl

Makefile

@@ -136,6 +136,10 @@ trace: .gopath
 	sh -c "PATH=$(PATHX) $(GOBUILD) -o trace ./go/cmd/trace"
 	$(FIXRPATH) trace
 
+com: .gopath
+	sh -c "PATH=$(PATHX) $(GOBUILD) -o com ./go/cmd/com"
+	$(FIXRPATH) com
+
 get: .gopath
 	sh -c "PATH=$(PATHX) go get -u ${DEPS}"
 

go/arch/x86_16/dos.go

@@ -83,12 +83,7 @@ func DosInit(u models.Usercorn, args, env []string) error {
 			u.RegWrite(enum, uint64(reg.Val))
 		}
 	}
-	u.RegWrite(u.Arch().SP, 0xbaaaaffc)
-	// TODO: Determine stack address. Right now making it linux x86 32-like
-	// with the stack ending at 0xC...
-	if err := u.MapStack(0xA000, 0x2000); err != nil {
-		return err
-	}
+	u.RegWrite(u.Arch().SP, 0x8000)
 	return nil
 }
 

go/cmd/com/com.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"bytes"
+	"github.com/pkg/errors"
+	"io/ioutil"
+	"os"
+
+	"github.com/lunixbochs/usercorn/go"
+	"github.com/lunixbochs/usercorn/go/cmd"
+	"github.com/lunixbochs/usercorn/go/loader"
+	"github.com/lunixbochs/usercorn/go/models"
+)
+
+func main() {
+	c := cmd.NewUsercornRawCmd()
+	c.NoArgs = true
+
+	c.MakeUsercorn = func(exe string) (models.Usercorn, error) {
+		p, err := ioutil.ReadFile(exe)
+		if err != nil {
+			return nil, err
+		}
+		r := bytes.NewReader(p)
+		l, err := loader.NewComLoader(r)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to load COM file")
+		}
+		u, err := usercorn.NewUsercornRaw(l, c.Config)
+
+		// Map in entire 16 bit address space
+		err = u.MemMapProt(0, 0x10000, 7)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to map in address space")
+		}
+
+		// Write in each segment's data
+		segments, err := l.Segments()
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to get segments from loader")
+		}
+		for _, seg := range segments {
+			data, err := seg.Data()
+			if err != nil {
+				return nil, errors.Wrap(err, "failed to read segment data")
+			}
+
+			err = u.MemWrite(seg.Addr, data)
+			if err != nil {
+				return nil, errors.Wrap(err, "failed to write segment data")
+			}
+		}
+
+		return u, nil
+	}
+	c.Run(os.Args, os.Environ())
+}

go/loader/com.go

@@ -24,7 +24,7 @@ func (c *ComLoader) OS() string {
 	return "DOS"
 }
 
-func NewComLoader(r io.ReaderAt, arch string) (models.Loader, error) {
+func NewComLoader(r io.ReaderAt) (models.Loader, error) {
 	// Calculate bin size
 	// TODO: We could maybe just pass the file, not the reader
 	buf := make([]byte, 0x1000)

go/loader/load.go

@@ -35,13 +35,6 @@ func LoadArch(r io.ReaderAt, arch string) (models.Loader, error) {
 	} else if MatchCgc(r) {
 		return NewCgcLoader(r, arch)
 	} else {
-		// TODO: Make COM a separate, explicit command
-		// COM doesn't have a header
-		loader, err := NewComLoader(r, arch)
-		if err != nil {
-			return nil, errors.WithStack(UnknownMagic)
-		} else {
-			return loader, err
-		}
+		return nil, errors.WithStack(UnknownMagic)
 	}
 }