Fully decompile xapi0

decompile/objdiff.json

@@ -50,7 +50,7 @@
       "target_path": "target/XDK/Xapi/xapi0.obj",
       "base_path": "src/XDK/Xapi/xapi0.obj",
       "metadata": {
-        "complete": false,
+        "complete": true,
         "source_path": "src/XDK/Xapi/xapi0.c"
       }
     }

decompile/src/XDK/Xapi/xapi0.c

@@ -21,11 +21,14 @@ extern struct IMAGE_TLS_DIRECTORY {
 	DWORD   SizeOfZeroFill;
 	DWORD   Characteristics;
 } _tls_used;
+extern int _tls_array;
+extern int _tls_index;
 
 extern int XapiTlsSize;
 
 DWORD __stdcall mainXapiStartup(LPVOID lpThreadParameter);
-BOOL  __stdcall CloseHandle    (HANDLE hHandle          );
+void  __stdcall XapiInitProcess(void);
+BOOL  __stdcall CloseHandle    (HANDLE hHandle);
 
 typedef DWORD (__stdcall * LPTHREAD_START_ROUTINE)(LPVOID lpThreadParameter);
 HANDLE __stdcall CreateThread(
@@ -43,18 +46,102 @@ void __stdcall XapiBootToDash(
 	DWORD dwParameter2
 );
 
+void __stdcall _rtinit(void);
+void __stdcall _cinit (void);
+
 
 // Every program is supposed to have a main(), so we can just assume its
-// existence with a declaration here
+// existence with a declaration here.  Interestingly, it's called with
-int main(void);
+// arguments here despite being declared without any on the developer's side.
+int main(
+	int      argc,
+	char * * argv,
+	char * * envp
+);
 
 
 // Address: 0x00147FB4
-// Status: unimplemented
+// Status: matching
-DWORD __stdcall mainXapiStartup(LPVOID lpThreadParameter) {
+__declspec(naked) DWORD __stdcall mainXapiStartup(LPVOID lpThreadParameter) {
-/* Runs some Xbox-specific initialization and then calls main() */
+/* Runs some Xbox-specific initialization and then calls main()
-	main();
+It appears to be truly impossible in Visual C++ 7.0 to access the FS register
-	return 0;
+without writing assembly, and also for inline assembly to write to a variable
+in a register rather than on the stack.  Thus, the only apparent way to make
+the middle part of the function match is through writing the instructions
+directly.  Given that the C parts of this function are so simple that a human
+and a compiler would reasonably produce the exact same code, and this function
+exhibits other oddities mentioned in the body, it's likely this whole function
+was originally written purely in assemblys.  In the spirit of decompilation,
+however, we'll lift what we can into C.
+*/
+	XapiInitProcess();
+
+	// Honestly unsure what's being done here, as FS doesn't seem to follow
+	// the same structure as 32-bit Windows
+	__asm {
+		mov  eax, fs:[0x20]
+		mov  eax, [eax+0x250]
+		test eax, eax
+		je   zero
+		mov  ecx, [eax+0x24]
+		jmp  store
+
+		/*
+		All this jumping around is strange, as it could easily be a
+		single branch, which is very plain to see if written out as C
+		(in fact, while MSVC's behaviour hasn't been tested, it
+		wouldn't take a very smart compiler to optimize this out if it
+		was written this way in C).  It seems likely this is awkward
+		human-written assembly.
+		*/
+	zero:
+		xor  ecx, ecx
+
+	store:
+		test ecx, ecx
+		je   end
+
+		/*
+		This section is suspect because of how it preserves edi despite
+		it not being used anywhere else, as if it was a separately
+		written function.  If it was a function, it must have been
+		inlined, but it couldn't be because it must be called from
+		assembly to use the value in ecx that never went on the stack
+		(as passing data from C to assembly has to do).  Notably, this
+		function's calling convention does require edi to be preserved,
+		but if left up to the compiler, it will push and pop edi in the
+		prologue and epilogue, not here (which this function must be
+		declared as naked to avoid).
+
+		It may be that this function was originally written entirely in
+		assembly and declared naked, with the author deciding to
+		preserve edi only in this one section using it.
+		*/
+		push edi
+		mov  eax, fs:[0x28]
+		mov  edi, fs:[_tls_array]
+		mov  edx, [_tls_index]
+		mov  edx, [edi + edx*0x4]
+		sub  edx, [eax + 0x28]
+		mov  byte ptr [ecx], 0x1
+		add  edx, _tls_array
+		mov  [ecx + 0x4], edx
+		pop  edi
+
+	end:
+	};
+
+	_rtinit();
+	_cinit();
+	main(0, NULL, NULL);
+
+	XapiBootToDash(XLD_LAUNCH_DASHBOARD_ERROR, XLD_ERROR_INVALID_XBE, 0);
+
+	// Return 0 to satisfy signature required for thread functions
+	_asm {
+		xor eax, eax
+		ret 4
+	};
 }
 
 // Address: 0x00148023

readme.md

@@ -3,7 +3,7 @@ A matching decompilation of the Xbox game Jet Set Radio Future.
 
 ## Progress
 - Delinking progress: 1.03% (26559 out of 2574172 bytes in XBE address space)
-- Decompilation progress: 19.0% (32 out of the 168 functions delinked so far)
+- Decompilation progress: 19.6% (33 out of the 168 functions delinked so far)
 - **Estimated total progress: 0.20%** (previous two multiplied together)
 
 ## Roadmap