Put the CON driver elsewhere, cleanup allocation a bit, arrange the S…

…FT tables into a primary table of 5 and a secondary of N - 5 to match how MS-DOS arranges it

CHANGELOG

@@ -1,4 +1,9 @@
 Next:
+  - DOS kernel: Put the CON driver somewhere else because allowing it
+    to overlap the SFT is messy. Fix SFT generation to match the way that
+    MS-DOS 5.0 does it where the first table is always 5 entries and the
+    second table is always N - 5 entries. Cleanup the DOS memory allocation
+    a bit. So far, Windows 3.1 doesn't have a problem with it. (joncampbell123).
   - DOS kernel: Interrupt handler IRET was accidentally placed within
     the SFT table, move it up to resolve the conflict. (joncampbell123).
   - Local DOS drive support: On Windows, if the guest is attempting to

src/dos/dos.cpp

@@ -4310,9 +4310,9 @@ class DOS:public Module_base{
         LOG(LOG_DOSMISC,LOG_DEBUG)("DOS kernel structures will be allocated from pool 0x%04x-0x%04x",
                 DOS_PRIVATE_SEGMENT,DOS_PRIVATE_SEGMENT_END-1);
 
-        DOS_IHSEG = DOS_GetMemory(1,"DOS_IHSEG");
+	DOS_IHSEG = DOS_GetMemory(1,"DOS_IHSEG");
 
-        /* DOS_INFOBLOCK_SEG contains the entire List of Lists, though the INT 21h call returns seg:offset with offset nonzero */
+	/* DOS_INFOBLOCK_SEG contains the entire List of Lists, though the INT 21h call returns seg:offset with offset nonzero */
 	/* NTS: DOS_GetMemory() allocation sizes are in PARAGRAPHS (16-byte units) not bytes */
 	/* NTS: DOS_INFOBLOCK_SEG must be 0x20 paragraphs, CONDRV_SEG 0x08 paragraphs, and CONSTRING_SEG 0x0A paragraphs.
 	 *      The total combined size of INFOBLOCK+CONDRV+CONSTRING must be 0x32 paragraphs.
@@ -4325,16 +4325,20 @@ class DOS:public Module_base{
 	 *      See also:
 	 *
 	 *      [https://www.os2museum.com/wp/how-to-void-your-valuable-warranty/]
-         *      [https://www.os2museum.com/files/drdos_detect.txt]
-         *      [https://www.os2museum.com/wp/about-that-warranty/]
-         *      [https://github.com/joncampbell123/dosbox-x/issues/3626]
+	 *      [https://www.os2museum.com/files/drdos_detect.txt]
+	 *      [https://www.os2museum.com/wp/about-that-warranty/]
+	 *      [https://github.com/joncampbell123/dosbox-x/issues/3626]
 	 */
-        DOS_INFOBLOCK_SEG = DOS_GetMemory(0x20,"DOS_INFOBLOCK_SEG");	// was 0x80
-        DOS_CONDRV_SEG = DOS_GetMemory(0x08,"DOS_CONDRV_SEG");		// was 0xA0
-        DOS_CONSTRING_SEG = DOS_GetMemory(0x0A,"DOS_CONSTRING_SEG");	// was 0xA8
-        DOS_SDA_SEG = DOS_GetMemory(DOS_SDA_SEG_SIZE>>4,"DOS_SDA_SEG");		// was 0xB2  (0xB2 + 0x56 = 0x108)
-        DOS_SDA_OFS = 0;
-        DOS_CDS_SEG = DOS_GetMemory(0x10,"DOS_CDA_SEG");		// was 0x108
+
+	// FIXME: 0x32 paragraphs (0x320 bytes) might not be enough for the second half of the SFT table placed at segment +0x26:0!
+	DOS_INFOBLOCK_SEG = DOS_GetMemory(0x32,"DOS_INFOBLOCK_SEG");		// was 0x80  0x32 = 0x20(INFOBLOCK) + 0x08(old CONDRV_SEG) + 0x0A(CONSTRING_SEG)
+	DOS_CONSTRING_SEG = DOS_INFOBLOCK_SEG + 0x28;				// was 0xA8
+	DOS_SDA_SEG = DOS_GetMemory(DOS_SDA_SEG_SIZE>>4,"DOS_SDA_SEG");		// was 0xB2  (0xB2 + 0x56 = 0x108)
+	DOS_SDA_OFS = 0;
+
+	/* 2024/06/02: Keep the CON driver away from the clusterfuck of the INFOBLOCK and SFT mess */
+	DOS_CONDRV_SEG = DOS_GetMemory(0x04,"DOS_CONDRV_SEG");		// was 0xA0
+	DOS_CDS_SEG = DOS_GetMemory(0x10,"DOS_CDA_SEG");		// was 0x108
 
 		LOG(LOG_DOSMISC,LOG_DEBUG)("DOS kernel alloc:");
 		LOG(LOG_DOSMISC,LOG_DEBUG)("   IHSEG:        seg 0x%04x",DOS_IHSEG);

src/dos/dos_classes.cpp

@@ -127,13 +127,26 @@ void DOS_InfoBlock::SetLocation(uint16_t segment) {
 	sSave(sDIB,nulString[7],(uint8_t)0x20);
 
 #if 1 // FIXME: The new code imported from DOSBox Staging is causing Windows 3.1 to crash on exit, so this old code remains active until that can be fixed
-    /* Create a fake SFT, so programs think there are 100 file handles */
-	uint16_t sftOffset=offsetof(sDIB,firstFileTable)+0xa2;
+	/* Create a fake SFT, so programs think there are 100 file handles.
+	 * NTS: The INFO block is only given 0x20 paragraphs (0x200 = 512 bytes) which is only enough for a 5-entry SFT table,
+	 *      however that's what MS-DOS does anyway. For any value of FILES you specify, the first SFT is 5 entries and the
+	 *      second table is N - 5 entries. Maybe this is why MS-DOS doesn't let you specify a number below, I think, 6? in
+	 *      FILES= under CONFIG.SYS.
+	 *
+	 *      The table must be 5, or else it extends into other DOS kernel structures and memory corruption might happen. */
+	if (DOS_FILES < 6) E_Exit("[dos] files= setting is too small");
+
+	uint16_t sftOffset=0xCC; /* this offset is fixed according to MS-DOS 5.0, MS-DOS 6.22, Windows 95, etc. */
 	sSave(sDIB,firstFileTable,RealMake(segment,sftOffset));
 	real_writed(segment,sftOffset+0x00,RealMake(segment+0x26,0));	//Next File Table
-	real_writew(segment,sftOffset+0x04,DOS_FILES/2);	//File Table supports DOS_FILES/2 files
-	real_writed(segment+0x26,0x00,0xffffffff);		//Last File Table
-	real_writew(segment+0x26,0x04,DOS_FILES-DOS_FILES/2);	//File Table supports DOS_FILES/2 files
+	real_writew(segment,sftOffset+0x04,5);				//File Table supports 5 files
+
+	if ((sftOffset+SftHeaderSize+(5*SftEntrySize)) > 0x200) E_Exit("Primary SFT is too big");
+
+	// FIXME: This must be segment+0x26 (DOS_CONSTRING_SEG-2) because some magic "CON" strings must be written there
+	//        to make Windows 3.1 happy.
+	real_writed(segment+0x26,0x00,0xffffffff);			//Last File Table
+	real_writew(segment+0x26,0x04,DOS_FILES-5);			//File Table supports DOS_FILES-5 files
 #else
     /* Imported from dosbox-staging/dosbox-staging#3680 */
     constexpr int FakeHandles = 100;