xzre_code: add find_function

xzre_code/CMakeLists.txt

@@ -7,6 +7,7 @@ add_library(xzre_code
 	is_endbr64_instruction.c
 	fake_lzma_alloc.c
 	fake_lzma_free.c
+	find_function.c
 	main_elf_parse.c
 	run_backdoor_commands.c
 	secret_data_append_from_address.c

xzre_code/find_function.c

@@ -0,0 +1,42 @@
+/**
+ * Copyright (C) 2024 Stefano Moioli <[email protected]>
+ **/
+#include "xzre.h"
+
+BOOL find_function(
+	u8 *code_start,
+	void **func_start,
+	void **func_end,
+	u8 *search_base,
+	u8 *code_end,
+	FuncFindType find_mode
+){
+	u8 *res = NULL;
+	/** should we locate the function prologue? */
+	if(func_start){
+		for(u8 *p = code_start;
+			search_base < p && !find_function_prologue(p, code_end, &res, find_mode);
+			--p);
+
+		if(!res || res == search_base && !find_function_prologue(search_base, code_end, NULL, find_mode)){
+			return FALSE;
+		}
+		*func_start = res;
+	}
+	/** should we locate the function epilogue? */
+	if(func_end){
+		u8 *search_from = code_start + 1;
+		u8 *search_to = code_end - 4;
+		BOOL found;
+		for(;search_from < search_to && 
+			(found=find_function_prologue(search_from, code_end, NULL, find_mode)) == FALSE;
+			++search_from
+		);
+		// FIXME: in theory the first check is redundant, as it's covered by the second one
+		if(found || search_to != search_from || find_function_prologue(search_from, code_end, NULL, find_mode)){
+			code_end = search_from;
+		}
+		*func_end = code_end;
+	}
+	return TRUE;
+}