binman: Add support for u-boot-tpl-bss-bad

This entry holds the padding between the end of of TPL binary and the
end of BSS. This region must be left empty so that the devicetree can be
appended correctly and remain accessible without interfering with BSS.

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

tools/binman/README.entries

@@ -1056,6 +1056,28 @@ binman uses that to look up symbols to write into the TPL binary.
 
 
 
+Entry: u-boot-tpl-bss-pad: U-Boot TPL binary padded with a BSS region
+---------------------------------------------------------------------
+
+Properties / Entry arguments:
+    None
+
+This holds the padding added after the TPL binary to cover the BSS (Block
+Started by Symbol) region. This region holds the various variables used by
+TPL. It is set to 0 by TPL when it starts up. If you want to append data to
+the TPL image (such as a device tree file), you must pad out the BSS region
+to avoid the data overlapping with U-Boot variables. This entry is useful in
+that case. It automatically pads out the entry size to cover both the code,
+data and BSS.
+
+The contents of this entry will a certain number of zero bytes, determined
+by __bss_size
+
+The ELF file 'tpl/u-boot-tpl' must also be available for this to work, since
+binman uses that to look up the BSS address.
+
+
+
 Entry: u-boot-tpl-dtb: U-Boot TPL device tree
 ---------------------------------------------
 

tools/binman/etype/u_boot_tpl_bss_pad.py

@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: GPL-2.0+
+# Copyright 2021 Google LLC
+# Written by Simon Glass <sjg@chromium.org>
+#
+# Entry-type module for BSS padding for tpl/u-boot-tpl.bin. This padding
+# can be added after the TPL binary to ensure that anything concatenated
+# to it will appear to TPL to be at the end of BSS rather than the start.
+#
+
+from binman import elf
+from binman.entry import Entry
+from binman.etype.blob import Entry_blob
+from patman import tools
+
+class Entry_u_boot_tpl_bss_pad(Entry_blob):
+    """U-Boot TPL binary padded with a BSS region
+
+    Properties / Entry arguments:
+        None
+
+    This holds the padding added after the TPL binary to cover the BSS (Block
+    Started by Symbol) region. This region holds the various variables used by
+    TPL. It is set to 0 by TPL when it starts up. If you want to append data to
+    the TPL image (such as a device tree file), you must pad out the BSS region
+    to avoid the data overlapping with U-Boot variables. This entry is useful in
+    that case. It automatically pads out the entry size to cover both the code,
+    data and BSS.
+
+    The contents of this entry will a certain number of zero bytes, determined
+    by __bss_size
+
+    The ELF file 'tpl/u-boot-tpl' must also be available for this to work, since
+    binman uses that to look up the BSS address.
+    """
+    def __init__(self, section, etype, node):
+        super().__init__(section, etype, node)
+
+    def ObtainContents(self):
+        fname = tools.GetInputFilename('tpl/u-boot-tpl')
+        bss_size = elf.GetSymbolAddress(fname, '__bss_size')
+        if not bss_size:
+            self.Raise('Expected __bss_size symbol in tpl/u-boot-tpl')
+        self.SetContents(tools.GetBytes(0, bss_size))
+        return True

tools/binman/ftest.py

@@ -4262,6 +4262,22 @@ class TestFunctional(unittest.TestCase):
         self.assertEqual(U_BOOT_TPL_NODTB_DATA,
                          data[:len(U_BOOT_TPL_NODTB_DATA)])
 
+    def testTplBssPad(self):
+        """Test that we can pad TPL's BSS with zeros"""
+        # ELF file with a '__bss_size' symbol
+        self._SetupTplElf()
+        data = self._DoReadFile('193_tpl_bss_pad.dts')
+        self.assertEqual(U_BOOT_TPL_DATA + tools.GetBytes(0, 10) + U_BOOT_DATA,
+                         data)
+
+    def testTplBssPadMissing(self):
+        """Test that a missing symbol is detected"""
+        self._SetupTplElf('u_boot_ucode_ptr')
+        with self.assertRaises(ValueError) as e:
+            self._DoReadFile('193_tpl_bss_pad.dts')
+        self.assertIn('Expected __bss_size symbol in tpl/u-boot-tpl',
+                      str(e.exception))
+
 
 if __name__ == "__main__":
     unittest.main()

tools/binman/test/193_tpl_bss_pad.dts

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/dts-v1/;
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	binman {
+		u-boot-tpl {
+		};
+
+		u-boot-tpl-bss-pad {
+		};
+
+		u-boot {
+		};
+	};
+};