Improve embedded PCK loading and exporting.

Windows export process:
  Limit size of executable with embedded PCK to 4 GB.
  Use "rcedit" before embedding PCK.
  Capture and process "rcedit" errors.

Windows, Linux:
  Add support for PCK loading from executable "pck" section.

3 files changed, 60 insertions, 15 deletions

diff --git a/core/io/file_access_pack.cpp b/core/io/file_access_pack.cpp
index c6e14ffee7..ba120de68b 100644
--- a/core/io/file_access_pack.cpp
+++ b/core/io/file_access_pack.cpp
@@ -32,6 +32,7 @@
 
 #include "core/io/file_access_encrypted.h"
 #include "core/object/script_language.h"
+#include "core/os/os.h"
 #include "core/version.h"
 
 #include <stdio.h>
@@ -131,32 +132,69 @@ bool PackedSourcePCK::try_open_pack(const String &p_path, bool p_replace_files,
 		return false;
 	}
 
-	f->seek(p_offset);
+	bool pck_header_found = false;
 
+	// Search for the header at the start offset - standalone PCK file.
+	f->seek(p_offset);
 	uint32_t magic = f->get_32();
+	if (magic == PACK_HEADER_MAGIC) {
+		pck_header_found = true;
+	}
 
-	if (magic != PACK_HEADER_MAGIC) {
-		// loading with offset feature not supported for self contained exe files
-		ERR_FAIL_COND_V_MSG(p_offset != 0, false, "Loading self-contained executable with offset not supported.");
+	// Search for the header in the executable "pck" section - self contained executable.
+	if (!pck_header_found) {
+		// Loading with offset feature not supported for self contained exe files.
+		if (p_offset != 0) {
+			ERR_FAIL_V_MSG(false, "Loading self-contained executable with offset not supported.");
+		}
 
-		//maybe at the end.... self contained exe
-		f->seek_end();
-		f->seek(f->get_position() - 4);
-		magic = f->get_32();
-		if (magic != PACK_HEADER_MAGIC) {
-			return false;
+		int64_t pck_off = OS::get_singleton()->get_embedded_pck_offset();
+		if (pck_off != 0) {
+			// Search for the header, in case PCK start and section have different alignment.
+			for (int i = 0; i < 8; i++) {
+				f->seek(pck_off);
+				magic = f->get_32();
+				if (magic == PACK_HEADER_MAGIC) {
+#ifdef DEBUG_ENABLED
+					print_verbose("PCK header found in executable pck section, loading from offset 0x" + String::num_int64(pck_off - 4, 16));
+#endif
+					pck_header_found = true;
+					break;
+				}
+				pck_off++;
+			}
 		}
-		f->seek(f->get_position() - 12);
+	}
 
-		uint64_t ds = f->get_64();
-		f->seek(f->get_position() - ds - 8);
+	// Search for the header at the end of file - self contained executable.
+	if (!pck_header_found) {
+		// Loading with offset feature not supported for self contained exe files.
+		if (p_offset != 0) {
+			ERR_FAIL_V_MSG(false, "Loading self-contained executable with offset not supported.");
+		}
 
+		f->seek_end();
+		f->seek(f->get_position() - 4);
 		magic = f->get_32();
-		if (magic != PACK_HEADER_MAGIC) {
-			return false;
+
+		if (magic == PACK_HEADER_MAGIC) {
+			f->seek(f->get_position() - 12);
+			uint64_t ds = f->get_64();
+			f->seek(f->get_position() - ds - 8);
+			magic = f->get_32();
+			if (magic == PACK_HEADER_MAGIC) {
+#ifdef DEBUG_ENABLED
+				print_verbose("PCK header found at the end of executable, loading from offset 0x" + String::num_int64(f->get_position() - 4, 16));
+#endif
+				pck_header_found = true;
+			}
 		}
 	}
 
+	if (!pck_header_found) {
+		return false;
+	}
+
 	uint32_t version = f->get_32();
 	uint32_t ver_major = f->get_32();
 	uint32_t ver_minor = f->get_32();
diff --git a/core/os/os.cpp b/core/os/os.cpp
index 846aeb16c5..4f7095b0fc 100644
--- a/core/os/os.cpp
+++ b/core/os/os.cpp
@@ -237,6 +237,11 @@ String OS::get_locale_language() const {
 	return get_locale().left(3).replace("_", "");
 }
 
+// Embedded PCK offset.
+uint64_t OS::get_embedded_pck_offset() const {
+	return 0;
+}
+
 // Helper function to ensure that a dir name/path will be valid on the OS
 String OS::get_safe_dir_name(const String &p_dir_name, bool p_allow_dir_separator) const {
 	Vector<String> invalid_chars = String(": * ? \" < > |").split(" ");
diff --git a/core/os/os.h b/core/os/os.h
index b3c66ff18c..9ec0dd7728 100644
--- a/core/os/os.h
+++ b/core/os/os.h
@@ -264,6 +264,8 @@ public:
 	virtual String get_locale() const;
 	String get_locale_language() const;
 
+	virtual uint64_t get_embedded_pck_offset() const;
+
 	String get_safe_dir_name(const String &p_dir_name, bool p_allow_dir_separator = false) const;
 	virtual String get_godot_dir_name() const;