binman: Support accessing binman tables at run time

Binman construct images consisting of multiple binary files. These files
sometimes need to know (at run timme) where their peers are located. For
example, SPL may want to know where U-Boot is located in the image, so
that it can jump to U-Boot correctly on boot.

In general the positions where the binaries end up after binman has
finished packing them cannot be known at compile time. One reason for
this is that binman does not know the size of the binaries until
everything is compiled, linked and converted to binaries with objcopy.

To make this work, we add a feature to binman which checks each binary
for symbol names starting with '_binman'. These are then decoded to figure
out which entry and property they refer to. Then binman writes the value
of this symbol into the appropriate binary. With this, the symbol will
have the correct value at run time.

Macros are used to make this easier to use. As an example, this declares
a symbol that will access the 'u-boot-spl' entry to find the 'pos' value
(i.e. the position of SPL in the image):

   binman_sym_declare(unsigned long, u_boot_spl, pos);

This converts to a symbol called '_binman_u_boot_spl_prop_pos' in any
binary that includes it. Binman then updates the value in that binary,
ensuring that it can be accessed at runtime with:

   ulong u_boot_pos = binman_sym(ulong, u_boot_spl, pos);

This assigns the variable u_boot_pos to the position of SPL in the image.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/elf.py

@@ -19,9 +19,6 @@ debug = False
 
 Symbol = namedtuple('Symbol', ['section', 'address', 'size', 'weak'])
 
-# Used for tests which don't have an ELF file to read
-ignore_missing_files = False
-
 
 def GetSymbols(fname, patterns):
     """Get the symbols from an ELF file
@@ -78,3 +75,55 @@ def GetSymbolAddress(fname, sym_name):
     if not sym:
         return None
     return sym.address
+
+def LookupAndWriteSymbols(elf_fname, entry, image):
+    """Replace all symbols in an entry with their correct values
+
+    The entry contents is updated so that values for referenced symbols will be
+    visible at run time. This is done by finding out the symbols positions in
+    the entry (using the ELF file) and replacing them with values from binman's
+    data structures.
+
+    Args:
+        elf_fname: Filename of ELF image containing the symbol information for
+            entry
+        entry: Entry to process
+        image: Image which can be used to lookup symbol values
+    """
+    fname = tools.GetInputFilename(elf_fname)
+    syms = GetSymbols(fname, ['image', 'binman'])
+    if not syms:
+        return
+    base = syms.get('__image_copy_start')
+    if not base:
+        return
+    for name, sym in syms.iteritems():
+        if name.startswith('_binman'):
+            msg = ("Image '%s': Symbol '%s'\n   in entry '%s'" %
+                   (image.GetPath(), name, entry.GetPath()))
+            offset = sym.address - base.address
+            if offset < 0 or offset + sym.size > entry.contents_size:
+                raise ValueError('%s has offset %x (size %x) but the contents '
+                                 'size is %x' % (entry.GetPath(), offset,
+                                                 sym.size, entry.contents_size))
+            if sym.size == 4:
+                pack_string = '<I'
+            elif sym.size == 8:
+                pack_string = '<Q'
+            else:
+                raise ValueError('%s has size %d: only 4 and 8 are supported' %
+                                 (msg, sym.size))
+
+            # Look up the symbol in our entry tables.
+            value = image.LookupSymbol(name, sym.weak, msg)
+            if value is not None:
+                value += base.address
+            else:
+                value = -1
+                pack_string = pack_string.lower()
+            value_bytes = struct.pack(pack_string, value)
+            if debug:
+                print('%s:\n   insert %s, offset %x, value %x, length %d' %
+                      (msg, name, offset, value, len(value_bytes)))
+            entry.data = (entry.data[:offset] + value_bytes +
+                        entry.data[offset + sym.size:])