all: use internal objcopy implementation

This lessens the dependency on binutils (e.g. arm-none-eabi-objcopy).

objcopy.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"debug/elf"
+	"os"
+	"path/filepath"
+
+	"github.com/marcinbor85/gohex"
+)
+
+// ObjcopyError is an error returned by functions that act like objcopy.
+type ObjcopyError struct {
+	Op  string
+	Err error
+}
+
+func (e ObjcopyError) Error() string {
+	if e.Err == nil {
+		return e.Op
+	}
+	return e.Op + ": " + e.Err.Error()
+}
+
+// ExtractTextSegment returns the .text segment and the first address from the
+// ELF file in the given path.
+func ExtractTextSegment(path string) (uint64, []byte, error) {
+	f, err := elf.Open(path)
+	if err != nil {
+		return 0, nil, ObjcopyError{"failed to open ELF file to extract text segment", err}
+	}
+	defer f.Close()
+
+	text := f.Section(".text")
+	if text == nil {
+		return 0, nil, ObjcopyError{"file does not contain .text segment: " + path, nil}
+	}
+	data, err := text.Data()
+	if err != nil {
+		return 0, nil, ObjcopyError{"failed to extract .text segment from ELF file", err}
+	}
+	return text.Addr, data, nil
+}
+
+// Objcopy converts an ELF file to a different (simpler) output file format:
+// .bin or .hex. It extracts only the .text section.
+func Objcopy(infile, outfile string) error {
+	f, err := os.OpenFile(outfile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	// Read the .text segment.
+	addr, data, err := ExtractTextSegment(infile)
+	if err != nil {
+		return err
+	}
+
+	// Write to the file, in the correct format.
+	switch filepath.Ext(outfile) {
+	case ".bin":
+		// The address is not stored in a .bin file (therefore you
+		// should use .hex files in most cases).
+		_, err := f.Write(data)
+		return err
+	case ".hex":
+		mem := gohex.NewMemory()
+		mem.SetStartAddress(uint32(addr)) // ignored in most cases (Intel-specific)
+		err := mem.AddBinary(uint32(addr), data)
+		if err != nil {
+			return ObjcopyError{"failed to create .hex file", err}
+		}
+		mem.DumpIntelHex(f, 32) // TODO: handle error
+		return nil
+	default:
+		panic("unreachable")
+	}
+}