elf: Fix SHA256 calculation

The comment says it returns the "SHA256 hash of the input ELF file", but this is
not true - it was the SHA256 hash of the output ELF file. As the parser may
change some bytes around in minor ways, these were often not the same.

components/espcoredump/corefile/elf.py

@@ -126,6 +126,8 @@ class ElfFile(object):
         self.load_segments = []  # type: list[ElfSegment]
         self.note_segments = []  # type: list[ElfNoteSegment]
 
+        self.sha256 = b''  # type: bytes
+
         if elf_path and os.path.isfile(elf_path):
             self.read_elf(elf_path)
 
@@ -156,6 +158,13 @@ class ElfFile(object):
                                     sec.data,
                                     sec.sh.sh_flags) for sec in self._model.sections]
 
+        # calculate sha256 of the input bytes (note: this may not be the same as the sha256 of any generated
+        # output struct, as the ELF parser may change some details.)
+        sha256 = hashlib.sha256()
+        sha256.update(elf_bytes)
+        self.sha256 = sha256.digest()
+
+
     @staticmethod
     def _parse_string_table(byte_str, offset):  # type: (bytes, int) -> str
         section_name_str = byte_str[offset:]
@@ -215,15 +224,6 @@ class ElfFile(object):
 
         return Struct(*args)
 
-    @property
-    def sha256(self):  # type: () -> bytes
-        """
-        :return: SHA256 hash of the input ELF file
-        """
-        sha256 = hashlib.sha256()
-        sha256.update(self._struct.build(self._model))  # type: ignore
-        return sha256.digest()
-
 
 class ElfSection(object):
     SHF_WRITE = 0x01