binman: Handle reading data for end-at-4gb sections

Some x86 sections have special offsets which currently result in empty
data being returned from the 'extract' command. Fix this by taking account
of the skip-at-start property.

Add a little more debugging while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Bin Meng <bmeng.cn@gmail.com>

tools/binman/entry.py

@@ -714,17 +714,19 @@ features to produce new behaviours.
         """
         # Use True here so that we get an uncompressed section to work from,
         # although compressed sections are currently not supported
+        tout.Debug("ReadChildData section '%s', entry '%s'" %
+                   (self.section.GetPath(), self.GetPath()))
         data = self.section.ReadChildData(self, decomp)
         return data
 
     def ReadChildData(self, child, decomp=True):
-        """Read the data for a particular child
+        """Read the data for a particular child entry
 
         This reads data from the parent and extracts the piece that relates to
         the given child.
 
         Args:
-            child: Child to read (must be valid)
+            child: Child entry to read data for (must be valid)
             decomp: True to decompress any compressed data before returning it;
                 False to return the raw, uncompressed data
 

tools/binman/etype/section.py

@@ -500,18 +500,12 @@ class Entry_section(Entry):
         return data
 
     def ReadChildData(self, child, decomp=True):
-        """Read the data for a particular child entry
-
-        Args:
-            child: Child entry to read data for
-            decomp: True to return uncompressed data, False to leave the data
-                compressed if it is compressed
-
-        Returns:
-            Data contents of entry
-        """
+        tout.Debug("ReadChildData for child '%s'" % child.GetPath())
         parent_data = self.ReadData(True)
-        data = parent_data[child.offset:child.offset + child.size]
+        offset = child.offset - self._skip_at_start
+        tout.Debug("Extract for child '%s': offset %#x, skip_at_start %#x, result %#x" %
+                   (child.GetPath(), child.offset, self._skip_at_start, offset))
+        data = parent_data[offset:offset + child.size]
         if decomp:
             indata = data
             data = tools.Decompress(indata, child.compress)

tools/binman/image.py

@@ -201,6 +201,8 @@ class Image(section.Entry_section):
         return entry
 
     def ReadData(self, decomp=True):
+        tout.Debug("Image '%s' ReadData(), size=%#x" %
+                   (self.GetPath(), len(self._data)))
         return self._data
 
     def GetListEntries(self, entry_paths):