binman: Handle writing ELF symbols in the Entry class

This feature is used by several etypes and we plan to add more that use
it. Make symbol writing a feature of the base class to reduce the code
duplication.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entry.py b/tools/binman/entry.py
index 63ec5ce..bdf53dd 100644
--- a/tools/binman/entry.py
+++ b/tools/binman/entry.py
@@ -12,6 +12,7 @@
 import time
 
 from binman import bintool
+from binman import elf
 from dtoc import fdt_util
 from patman import tools
 from patman.tools import to_hex, to_hex_size
@@ -86,10 +87,15 @@
         fake_fname: Fake filename, if one was created, else None
         required_props (dict of str): Properties which must be present. This can
             be added to by subclasses
+        elf_fname (str): Filename of the ELF file, if this entry holds an ELF
+            file, or is a binary file produced from an ELF file
+        auto_write_symbols (bool): True to write ELF symbols into this entry's
+            contents
     """
     fake_dir = None
 
-    def __init__(self, section, etype, node, name_prefix=''):
+    def __init__(self, section, etype, node, name_prefix='',
+                 auto_write_symbols=False):
         # Put this here to allow entry-docs and help to work without libfdt
         global state
         from binman import state
@@ -125,6 +131,8 @@
         self.fake_fname = None
         self.required_props = []
         self.comp_bintool = None
+        self.elf_fname = None
+        self.auto_write_symbols = auto_write_symbols
 
     @staticmethod
     def FindEntryClass(etype, expanded):
@@ -647,7 +655,8 @@
         Args:
           section: Section containing the entry
         """
-        pass
+        if self.auto_write_symbols:
+            elf.LookupAndWriteSymbols(self.elf_fname, self, section.GetImage())
 
     def CheckEntries(self):
         """Check that the entry offsets are correct