build: (Custom) App version info is now on a dedicated section, independent of the rodata alignment

It is now possible to have any alignment restriction on rodata in the user
applicaiton. It will not affect the first section which must be aligned
on a 16-byte bound.

Closes https://github.com/espressif/esp-idf/issues/6719

tools/test_apps/build_system/ldalign_test/check_alignment.py

@@ -0,0 +1,64 @@
+#!/usr/bin/env python
+#
+# Copyright 2020 Espressif Systems (Shanghai) PTE LTD
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import argparse
+import re
+import subprocess
+from typing import Tuple
+
+argparser = argparse.ArgumentParser()
+
+argparser.add_argument('readelf')
+argparser.add_argument('elf')
+
+args = argparser.parse_args()
+
+# Get the content of the readelf command
+contents = subprocess.check_output([args.readelf, '-S', args.elf]).decode()
+
+
+# Define a class for readelf parsing error
+class ParsingError(Exception):
+    pass
+
+
+# Look for the start address and size of any section
+def find_partition_info(sectionname):  # type: (str) -> Tuple[int, int, int]
+    match = re.search(sectionname + r'\s+PROGBITS\s+([a-f0-9]+) [a-f0-9]+ ([a-f0-9]+) \d+\s+[A-Z]+  0   0 (\d+)',
+                      contents)
+    if not match:
+        raise ParsingError('ELF header parsing error')
+    # Return the address of the section, the size and the alignment
+    address = match.group(1)
+    size = match.group(2)
+    alignment = match.group(3)
+    return (int(address, 16), int(size, 16), int(alignment, 10))
+
+
+# Get address and size for .flash.appdesc section
+app_address, app_size, app_align = find_partition_info('.flash.appdesc')
+
+# Same goes for .flash.rodata section
+rodata_address, _, rodata_align = find_partition_info('.flash.rodata')
+
+# Assert than everything is as expected:
+# appdesc is aligned on 16
+# rodata is aligned on 64
+# appdesc ends where rodata starts
+assert app_align == 16, '.flash.appdesc section should have been aligned on 16!'
+assert rodata_align == 64, '.flash.rodata section should have been aligned on 64!'
+assert app_address + app_size == rodata_address, ".flash.appdesc's end address and .flash.rodata's begin start must have no gap in between!"