QVM: reuse rounded up data segment space for extra pStack if possible

ec- · Jan 25, 2025 · 8aa6fa1 · 8aa6fa1
1 parent 01eaea8
commit 8aa6fa1
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Showing 2 changed files with 25 additions and 11 deletions.
diff --git a/code/qcommon/vm.c b/code/qcommon/vm.c
@@ -748,7 +748,6 @@ static vmHeader_t *VM_LoadQVM( vm_t *vm, qboolean alloc ) {
 	int					length;
 	unsigned int		dataLength;
 	unsigned int		dataAlloc;
-	int					i;
 	char				filename[MAX_QPATH], *errorMsg;
 	unsigned int		crc32sum;
 	qboolean			tryjts;
@@ -788,17 +787,31 @@ static vmHeader_t *VM_LoadQVM( vm_t *vm, qboolean alloc ) {
 	}
 
 	vm->exactDataLength = header->dataLength + header->litLength + header->bssLength;
-	dataLength = vm->exactDataLength + PROGRAM_STACK_EXTRA;
-	if ( dataLength < PROGRAM_STACK_SIZE + PROGRAM_STACK_EXTRA ) {
-		dataLength = PROGRAM_STACK_SIZE + PROGRAM_STACK_EXTRA;
+
+	dataLength = vm->exactDataLength;
+	if ( dataLength < PROGRAM_STACK_SIZE ) {
+		dataLength = PROGRAM_STACK_SIZE;
+	}
+
+	vm->programStackExtra = PROGRAM_STACK_EXTRA;
+
+	// if rounding difference is larger than extra space we need then reuse it
+	if ( log2pad( dataLength, 1 ) - dataLength >= PROGRAM_STACK_EXTRA ) {
+#ifdef _DEBUG
+		// keep exact size for debug purposes
+#else
+		// reuse it all for release builds
+		vm->programStackExtra = log2pad( dataLength, 1 ) - dataLength;
+		// Com_DPrintf( S_COLOR_CYAN "%s: reuse %i bytes for pStack\n", vm->name, vm->programStackExtra );
+#endif
+	} else {
+		dataLength += vm->programStackExtra;
 	}
+
 	vm->dataLength = dataLength;
 
-	// round up to next power of 2 so all data operations can
-	// be mask protected
-	for ( i = 0 ; dataLength > ( 1 << i ) ; i++ )
-		;
-	dataLength = 1 << i;
+	// round up to next power of 2 so all data operations can be mask protected
+	dataLength = log2pad( dataLength, 1 );
 
 	// reserve some space for effective LOCAL+LOAD* checks
 	dataAlloc = dataLength + VM_DATA_GUARD_SIZE;
@@ -825,7 +838,7 @@ static vmHeader_t *VM_LoadQVM( vm_t *vm, qboolean alloc ) {
 					"VM_Restart()\n", filename );
 			return NULL;
 		}
-		Com_Memset( vm->dataBase, 0, vm->dataAlloc );
+		Com_Memset( vm->dataBase, 0x0, vm->dataAlloc );
 	}
 
 	// copy the intialized data
@@ -1801,7 +1814,7 @@ vm_t *VM_Create( vmIndex_t index, syscall_t systemCalls, dllSyscall_t dllSyscall
 
 	// the stack is implicitly at the end of the image
 	vm->programStack = vm->dataMask + 1;
-	vm->stackBottom = vm->programStack - PROGRAM_STACK_SIZE - PROGRAM_STACK_EXTRA;
+	vm->stackBottom = vm->programStack - PROGRAM_STACK_SIZE - vm->programStackExtra;
 
 	vm->compiled = qfalse;
 

diff --git a/code/qcommon/vm_local.h b/code/qcommon/vm_local.h
@@ -203,6 +203,7 @@ struct vm_s {
 	uint32_t	dataLength;			// data segment length
 	uint32_t	exactDataLength;	// from qvm header
 	uint32_t	dataAlloc;			// actually allocated, for mmap()/munmap()
+	uint32_t	programStackExtra;
 
 	int			numSymbols;
 	vmSymbol_t	*symbols;