mfg split: Don't discard trailing 0xff bytes

The `mfg split` command separates an mfgimg binary into several files,
one for each flash area.

Prior to this commit, imgmod would strip all trailing erase-val bytes
(0xff) from each file.  Usually this was the correct behavior, but if
the contents of a flash area legitimately ended with an erase-val byte,
then the file would be corrupted during this step.

The problem is that `newt` was throwing away information when it created
mfgimages.  It embedded the specified binaries into a single mfgimage
and filled in the gaps with erase-val bytes, and it did this without
leaving any indication of the sizes of the binaries used as input.

Newt was recently changed to include the sizes of these binaries in the
`manifest.json` file that accompanies an mfgimage.  This commit changes
imgmod to read these sizes from the manifest file so that it knows how
many erase-val bytes it can safely strip.

If the manifest does not contain size information (backwards
compatibility), imgmod falls back to the old behavior or stripping all
trailing erase-val bytes.

Author: ccollins476ad

cli/mfg_cmds.go

@@ -184,7 +184,7 @@ func runSplitCmd(cmd *cobra.Command, args []string) {
 		ImgmodUsage(nil, err)
 	}
 
-	nbmap, err := imfg.Split(bin, man.Device, areas, man.EraseVal)
+	nbmap, err := imfg.Split(bin, man, areas)
 	if err != nil {
 		ImgmodUsage(nil, err)
 	}

imfg/imfg.go

@@ -28,6 +28,7 @@ import (
 
 	"github.com/apache/mynewt-artifact/errors"
 	"github.com/apache/mynewt-artifact/flash"
+	"github.com/apache/mynewt-artifact/manifest"
 	"github.com/apache/mynewt-artifact/mfg"
 	"mynewt.apache.org/imgmod/iutil"
 )
@@ -78,8 +79,63 @@ func VerifyAreas(areas []flash.FlashArea) error {
 	return nil
 }
 
-func Split(mfgBin []byte, deviceNum int,
-	areas []flash.FlashArea, eraseVal byte) (NameBlobMap, error) {
+// areaDataEnd calculates the end offset of valid data in a flash area.  "Valid
+// data" includes all target binaries and raw sections.  If it cannot determine
+// the end of any constituent part, it returns an error.
+func areaDataEnd(area flash.FlashArea, man manifest.MfgManifest) (int, error) {
+	end := 0
+
+	// Updates `end` if the specified region extends beyond our current concept
+	// of "the end".
+	checkOne := func(offset int, size int) error {
+		a := man.FindWithinFlashAreaDevOff(man.Device, offset)
+		if a.Id != area.Id {
+			// Data belongs to a different area.
+			return nil
+		}
+
+		// Older manifests do not contain target size information.
+		if size <= 0 {
+			return errors.Errorf(
+				"failed to calculate end offset of data at %d: "+
+					"manifest lacks size",
+				offset)
+		}
+
+		subEnd := offset - a.Offset + size
+		if subEnd > end {
+			end = subEnd
+		}
+
+		return nil
+	}
+
+	for _, t := range man.Targets {
+		err := checkOne(t.Offset, t.Size)
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	for _, r := range man.Raws {
+		err := checkOne(r.Offset, r.Size)
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	if man.Meta != nil {
+		err := checkOne(man.Meta.EndOffset-1, 1)
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	return end, nil
+}
+
+func Split(mfgBin []byte, man manifest.MfgManifest,
+	areas []flash.FlashArea) (NameBlobMap, error) {
 
 	mm := NameBlobMap{}
 
@@ -89,7 +145,7 @@ func Split(mfgBin []byte, deviceNum int,
 				"two or more flash areas with same name: \"%s\"", area.Name)
 		}
 
-		if area.Device == deviceNum {
+		if area.Device == man.Device {
 			var areaBin []byte
 			if area.Offset < len(mfgBin) {
 				end := area.Offset + area.Size
@@ -100,7 +156,17 @@ func Split(mfgBin []byte, deviceNum int,
 				areaBin = mfgBin[area.Offset:end]
 			}
 
-			mm[area.Name] = StripPadding(areaBin, eraseVal)
+			dataEnd, err := areaDataEnd(area, man)
+			if err != nil {
+				// Failed to determine the data end offset.  Just strip all
+				// trailing erase-val bytes.
+				areaBin = StripPadding(areaBin, man.EraseVal)
+			} else {
+				areaBin = areaBin[:dataEnd]
+			}
+			if len(areaBin) > 0 {
+				mm[area.Name] = areaBin
+			}
 		}
 	}