dosbox-staging · kcgen · Mar 5, 2023 · Mar 4, 2023 · Mar 4, 2023 · Mar 4, 2023
diff --git a/.github/workflows/windows-msvc.yml b/.github/workflows/windows-msvc.yml
@@ -23,7 +23,7 @@ jobs:
             max_warnings: 20
           - name: MSVC 64-bit
             arch: x64
-            max_warnings: 910
+            max_warnings: 904
     steps:
       - name: Checkout repository
         uses: actions/checkout@v3

diff --git a/include/dos_system.h b/include/dos_system.h
@@ -380,6 +380,16 @@ void DOS_AddDevice(DOS_Device * adddev);
 /* DelDevice destroys the device that is pointed to. */
 void DOS_DelDevice(DOS_Device * dev);
 
+// Get, append, and query the DOS device header linked list
+RealPt DOS_GetNextDevice(const RealPt rp);
+RealPt DOS_GetLastDevice();
+void DOS_AppendDevice(const uint16_t segment, const uint16_t offset = 0);
+bool DOS_IsLastDevice(const RealPt rp);
+bool DOS_DeviceHasName(const RealPt rp, const std::string_view req_name);
+bool DOS_DeviceHasAttributes(const RealPt rp, const uint16_t attributes);
+uint16_t DOS_GetDeviceStrategy(const RealPt rp);
+uint16_t DOS_GetDeviceInterrupt(const RealPt rp);
+
 void VFILE_Register(const char *name,
                     const uint8_t *data,
                     const uint32_t size,

diff --git a/src/dos/dos_devices.cpp b/src/dos/dos_devices.cpp
@@ -191,54 +191,64 @@ uint8_t DOS_ExtDevice::GetStatus(bool input_flag)
 	return 0x00;
 }
 
-uint32_t DOS_CheckExtDevice(const char *name, bool already_flag)
+// Walk the DOS devices and return the real pointer to the device matching the
+// given name, provided it's not an existing driver (if indicated).
+RealPt DOS_CheckExtDevice(const std::string_view name, const bool skip_existing_drivers)
 {
-	uint32_t addr = dos_infoblock.GetDeviceChain();
-	uint16_t seg, off;
-	uint16_t next_seg, next_off;
-	uint16_t no;
-	char devname[8 + 1];
-
-	seg = addr >> 16;
-	off = addr & 0xffff;
-	while (1) {
-		no = real_readw(seg, off + 4);
-		next_seg = real_readw(seg, off + 2);
-		next_off = real_readw(seg, off);
-		if (next_seg == 0xffff && next_off == 0xffff) {
-			break;
-		}
-		if (no & 0x8000) {
-			for (no = 0; no < 8; no++) {
-				if ((devname[no] = real_readb(seg, off + 10 + no)) <= 0x20) {
-					devname[no] = 0;
-					break;
-				}
+	// Helper lambda's to check various device properties
+	//
+	auto is_a_driver = [](const RealPt rp) {
+		constexpr uint16_t driver_flag = (1 << 15);
+		return DOS_DeviceHasAttributes(rp, driver_flag);
+	};
+
+	auto is_con_or_nul = [](const RealPt rp) {
+		constexpr uint16_t con_strategy  = 0;
+		constexpr uint16_t con_interrupt = 0;
+
+		constexpr uint16_t nul_strategy  = 0xffff;
+		constexpr uint16_t nul_interrupt = 0xffff;
+
+		const auto strategy  = DOS_GetDeviceStrategy(rp);
+		const auto interrupt = DOS_GetDeviceInterrupt(rp);
+
+		return (strategy == con_strategy && interrupt == con_interrupt) ||
+		       (strategy == nul_strategy && interrupt == nul_interrupt);
+	};
+
+	auto is_existing_driver = [](const RealPt rp) {
+		for (const auto& dev : Devices) {
+			if (!dev || (dev->GetInformation() & EXT_DEVICE_BIT) == 0) {
+				continue;
 			}
-			devname[8] = 0;
-			if (!strcmp(name, devname)) {
-				if (already_flag) {
-					for (no = 0; no < DOS_DEVICES; no++) {
-						if (Devices[no]) {
-							if (Devices[no]->GetInformation() & EXT_DEVICE_BIT) {
-								if (((DOS_ExtDevice *)Devices[no])
-								            ->CheckSameDevice(seg, real_readw(seg, off + 6),
-								                              real_readw(seg, off + 8))) {
-									return 0;
-								}
-							}
-						}
-					}
-				}
-				// Exclude the default CON and NUL
-				if (real_readd(seg, off + 6) == 0 || real_readd(seg, off + 6) == 0xffffffff) {
-					return 0;
-				}
-				return (uint32_t)seg << 16 | (uint32_t)off;
+			const auto ext_dev = dynamic_cast<DOS_ExtDevice*>(dev);
+			if (ext_dev->CheckSameDevice(RealSeg(rp),
+			                             DOS_GetDeviceStrategy(rp),
+			                             DOS_GetDeviceInterrupt(rp))) {
+				return true;
 			}
 		}
-		seg = next_seg;
-		off = next_off;
+		return false;
+	};
+
+	// start walking the device chain of real pointers
+	auto rp = dos_infoblock.GetDeviceChain();
+
+	while (!DOS_IsLastDevice(rp)) {
+		if (!is_a_driver(rp) || !DOS_DeviceHasName(rp, name)) {
+			rp = DOS_GetNextDevice(rp);
+			continue;
+		}
+		if (is_con_or_nul(rp)) {
+			return 0;
+		}
+		if (skip_existing_drivers && is_existing_driver(rp)) {
+			return 0;
+		}
+		// The device at the real pointer is a driver, has a name
+		// matching the given name, is neither the CON nor NUL devices,
+		// and (if requested) is not an existing device driver.
+		return rp;
 	}
 	return 0;
 }
@@ -420,6 +430,106 @@ void DOS_DelDevice(DOS_Device * dev) {
 	}
 }
 
+// Structure of internal DOS tables, Device Driver
+//
+// Property   Offset  Type      Description
+// ~~~~~~~~   ~~~~~~  ~~~~~     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// next_rpt   00h     DWord --> Next driver in chain (x:FFFF means end)
+// attributes 04h     Word      Device attributes.
+// strategy   06h     Word      Device strategy routine offset.
+// interrupt  08h     Word      Device interrupt routine offset.
+// name       0Ah     8 Bytes   Device name padded with spaces.
+//
+// Ref: https://www.infradeaorg/devload/DOSTables.html, Appendix 2
+//
+namespace DeviceDriverInfo {
+constexpr uint8_t next_rpt_offset = 0x00;   // DWORD, points to next driver in
+                                            // chain (x:FFFF means end)
+constexpr uint8_t attributes_offset = 0x04; // WORD, device attributes offset
+constexpr uint8_t strategy_offset   = 0x06; // WORD, device strategy routine
+                                            // offset.
+constexpr uint8_t interrupt_offset = 0x08;  // WORD, device interrupt
+                                            // routine offset.
+constexpr uint8_t name_offset = 0x0a;       // 8 bytes, device name padded with
+                                            // spaces.
+constexpr size_t name_length = 8;
+} // namespace DeviceDriverInfo
+
+// Indicates if the device at the given real pointer is the last in DOS's chain
+bool DOS_IsLastDevice(const RealPt rp)
+{
+	constexpr uint16_t last_offset_marker = 0xffff;
+	return RealOff(rp) == last_offset_marker;
+}
+
+// From the given real pointer, get the next device driver's real pointer
+RealPt DOS_GetNextDevice(const RealPt rp)
+{
+	return real_readd(RealSeg(rp),
+	                  RealOff(rp) + DeviceDriverInfo::next_rpt_offset);
+}
+
+// Get the tail real pointer from the DOS device driver linked list
+RealPt DOS_GetLastDevice()
+{
+	auto rp = dos_infoblock.GetDeviceChain();
+
+	while (!DOS_IsLastDevice(rp)) {
+		rp = DOS_GetNextDevice(rp);
+	}
+	return rp;
+}
+
+// Append the device at the given address to the end of the DOS device linked list
+void DOS_AppendDevice(const uint16_t segment, const uint16_t offset)
+{
+	const auto new_rp  = RealMake(segment, offset);
+	const auto tail_rp = DOS_GetLastDevice();
+	real_writed(RealSeg(tail_rp), RealOff(tail_rp), new_rp);
+}
+
+bool DOS_DeviceHasAttributes(const RealPt rp, const uint16_t req_attributes)
+{
+	const auto attributes = real_readw(
+	        RealSeg(rp), RealOff(rp) + DeviceDriverInfo::attributes_offset);
+
+	return (attributes & req_attributes) == req_attributes;
+}
+
+uint16_t DOS_GetDeviceStrategy(const RealPt rp)
+{
+	return real_readw(RealSeg(rp),
+	                  RealOff(rp) + DeviceDriverInfo::strategy_offset);
+}
+
+uint16_t DOS_GetDeviceInterrupt(const RealPt rp)
+{
+	return real_readw(RealSeg(rp),
+	                  RealOff(rp) + DeviceDriverInfo::interrupt_offset);
+}
+
+bool DOS_DeviceHasName(const RealPt rp, const std::string_view req_name)
+{
+	const auto segment    = RealSeg(rp);
+	const auto offset     = RealOff(rp) + DeviceDriverInfo::name_offset;
+
+	const auto search_len = std::min(req_name.length(),
+	                                 DeviceDriverInfo::name_length);
+
+	for (uint8_t i = 0; i < search_len; ++i) {
+		// source and requested characters
+		const auto s = real_readb(segment, check_cast<uint16_t>(offset + i));
+		const auto r = req_name[i];
+		if (r == '\0') {
+			break;
+		}
+		if (r != static_cast<char>(s)) {
+			return false;
+		}
+	}
+	return true;
+}
+
 void DOS_SetupDevices() {
 	DOS_Device * newdev;
 	newdev=new device_CON();

diff --git a/src/dos/dos_mscdex.cpp b/src/dos/dos_mscdex.cpp
@@ -351,15 +351,7 @@ int CMscdex::AddDrive(uint16_t _drive, char* physicalPath, uint8_t& subUnit)
 		devHeader.SetName				("MSCD001 ");
 
 		//Link it in the device chain
-		uint32_t start = dos_infoblock.GetDeviceChain();
-		uint16_t segm  = (uint16_t)(start>>16);
-		uint16_t offm  = (uint16_t)(start&0xFFFF);
-		while(start != 0xFFFFFFFF) {
-			segm  = (uint16_t)(start>>16);
-			offm  = (uint16_t)(start&0xFFFF);
-			start = real_readd(segm,offm);
-		}
-		real_writed(segm,offm,seg<<16);
+		DOS_AppendDevice(seg);
 
 		// Create Callback Strategy
 		uint16_t off = sizeof(DOS_DeviceHeader::sDeviceHeader);