create-diff-object: Add support for arm64 DYNAMIC_FTRACE_WITH_CALL_OPS

For arm64 this option uses -fpatchable-function-entry=M,2, so 2 NOPs
are placed before the function entry point (in order to store a pointer
to ftrace_ops). When calculating function padding, check for the
presence of the two NOPs, and adjust the padding size by 8 if they are
found.

Author: dylanbhatch

kpatch-build/create-diff-object.c

@@ -250,6 +250,36 @@ static bool kpatch_is_mapping_symbol(struct kpatch_elf *kelf, struct symbol *sym
 	return false;
 }
 
+static unsigned int function_padding_size(struct kpatch_elf *kelf, struct symbol *sym)
+{
+	unsigned int size = 0;
+
+	switch (kelf->arch) {
+	case AARCH64:
+	{
+		uint32_t *insn = sym->sec->data->d_buf;
+		unsigned int i;
+		void *insn_end = sym->sec->data->d_buf + sym->sym.st_value;
+
+		/*
+		 * Check for exactly two NOPs (0xd503201f), used to store a
+		 * pointer to ftrace call ops when DYNAMIC_FTRACE_WITH_CALL_OPS
+		 * is enbled.
+		 */
+		for (i = 0; (void *)insn < insn_end && *insn == 0xd503201f; i++, insn++)
+			;
+
+		if (i == 2)
+			size = 8;
+		break;
+	}
+	default:
+		break;
+	}
+
+	return size;
+}
+
 /*
  * When compiling with -ffunction-sections and -fdata-sections, almost every
  * symbol gets its own dedicated section.  We call such symbols "bundled"
@@ -266,6 +296,8 @@ static void kpatch_bundle_symbols(struct kpatch_elf *kelf)
 				expected_offset = 16;
 			else if (is_gcc6_localentry_bundled_sym(kelf, sym))
 				expected_offset = 8;
+			else if (sym->type == STT_FUNC)
+				expected_offset = function_padding_size(kelf, sym);
 			else
 				expected_offset = 0;