Checkpoint: many many changes, now successfully loads the

target OS bootsector, but then fails at a later point.

4 files changed, 110 insertions, 73 deletions

diff --git a/memdisk/e820func.c b/memdisk/e820func.c
index d9c8465a..4d0ec150 100644
--- a/memdisk/e820func.c
+++ b/memdisk/e820func.c
@@ -30,7 +30,8 @@ void e820map_init(void)
 {
   nranges = 1;
   asm volatile("cld ; rep ; stosl %0,%%es:(%1)"
-	       :: "a" (0), "S" (ranges), "c" (sizeof(ranges) >> 2));
+	       :: "a" (0), "D" (ranges), "c" (sizeof(ranges) >> 2)
+	       : "edi", "ecx");
   ranges[1].type = -1;
 }
 
diff --git a/memdisk/init.S16 b/memdisk/init.S16
index 955e8726..2e87d1dc 100644
--- a/memdisk/init.S16
+++ b/memdisk/init.S16
@@ -72,11 +72,7 @@ setup_move_size: .word  0		# Unused
 
 code32_start:				# here loaders can put a different
 					# start address for 32-bit code.
-#ifndef __BIG_KERNEL__
-		.long	0x1000		#   0x1000 = default for zImage
-#else
 		.long	0x100000	# 0x100000 = default for big kernel
-#endif
 
 ramdisk_image:	.long	0		# address of loaded ramdisk image
 					# Here the loader puts the 32-bit
diff --git a/memdisk/memdisk.asm b/memdisk/memdisk.asm
index ddaf100b..6688f0ec 100644
--- a/memdisk/memdisk.asm
+++ b/memdisk/memdisk.asm
@@ -22,8 +22,6 @@
 %define SECTORSIZE_LG2	9		; log2(sector size)
 %define	SECTORSIZE	(1 << SECTORSIZE_LG2)
 
-MyStack		equ 1024
-
 		; Parameter registers definition; this is the definition
 		; of the stack frame.
 %define		P_DS		word [bp+34]
@@ -65,12 +63,12 @@ Int13Start:
 		xor dl,[cs:DriveNo]
 		pop dx
 		js .nomatch		; If SF=0, we have a match here
+		jz .our_drive		; If ZF=1, we have an exact match
 		cmp dl,[cs:DriveNo]
-		je .our_drive
 		jb .nomatch		; Drive < Our drive
 		dec dl			; Drive > Our drive, adjust drive #
 .nomatch:
-		jmp far [OldInt13]
+		jmp far [cs:OldInt13]
 
 .our_drive:
 		mov [cs:Stack],esp
@@ -79,33 +77,36 @@ Int13Start:
 		mov [cs:Stack+4],ax
 		mov ax,cs
 		mov ss,ax
-		mov sp,MyStack
+		mov sp,[cs:MyStack]
 		push ds
 		push es
 		mov ds,ax
 		mov es,ax
 		mov ax,[SavedAX]
 		pushad
-		mov bp,sp
+		mov bp,sp		; Point BP to the entry stack frame
 		cmp ah,Int13FuncsMax
 		jae Invalid
 		xor al,al		; AL = 0 is standard entry condition
 		mov di,ax
-		shr di,7
+		shr di,7		; Convert AH to an offset in DI
 		call [Int13Funcs+di]
 
 Done:		; Standard routine for return
-		mov [LastStatus],ah
 		mov P_AX,ax
-		cmp ah,1
 DoneWeird:
-		setnb al		; AL <- (AH > 0) ? 1 : 0 (CF)
-		lds ebx,[Stack]		; DS:EBX <- Old stack pointer
-		mov [ebx+4],al		; Low byte of old FLAGS -> arithmetric flags
+		mov [LastStatus],ah
+		and ah,ah
+
 		popad
 		pop es
 		pop ds
 		lss esp,[cs:Stack]
+
+		; This sets the low byte (the arithmetric flags) of the
+		; FLAGS on stack to either 00h (no flags) or 01h (CF)
+		; depending on if AH was zero or not.
+		setnz [esp+4]		; Set CF iff error
 		iret
 
 Reset:
@@ -117,14 +118,13 @@ Reset:
 		pop ds
 		lss esp,[cs:Stack]
 		and dl,80h		; Clear all but the type bit
-		jmp far [OldInt13]
+		jmp far [cs:OldInt13]
 
 Invalid:
 		mov ax,0100h		; Unsupported function
 		ret
 
 GetDriveType:
-		pop ax			; Drop return address
 		mov ah,[DriveNo]
 		shr ah,7
 		pushf
@@ -137,21 +137,14 @@ GetDriveType:
 		mov ax,[DiskSize+2]
 		mov P_CX,ax
 .floppy:
-		mov [LastStatus],byte 0	; Success, but AH returns a value
-		jmp short DoneWeird
+		pop ax			; Drop return address
+		xor ax,ax		; Success...
+		jmp short DoneWeird	; But don't stick it into P_AX
 
 GetStatus:
 		mov ah,[LastStatus]	; Copy last status
 		ret
 
-CheckIfReady:				; These are always-successful noop functions
-Recalibrate:
-InitWithParms:
-DetectChange:
-success:
-		xor ax,ax		; Always successful
-		ret
-
 Read:
 		call setup_regs
 do_copy:
@@ -161,7 +154,7 @@ do_copy:
 
 Write:
 		call setup_regs
-		xchg esi,edi
+		xchg esi,edi		; Opposite direction of a Read!
 		jmp short do_copy
 
 		; These verify one sector only
@@ -171,7 +164,15 @@ Seek:
 		; Verify integrity; just bounds-check
 Verify:
 		call setup_regs		; Returns error if appropriate
-		jmp short success	
+		; And fall through to success
+
+CheckIfReady:				; These are always-successful noop functions
+Recalibrate:
+InitWithParms:
+DetectChange:
+success:
+		xor ax,ax		; Always successful
+		ret
 
 GetParms:
 		; We need to get the "number of drives" from the BIOS
@@ -197,44 +198,46 @@ GetParms:
 		xor ax,ax
 		ret
 
-		; Convert a CHS address in CX/DH into an LBA in EAX
-chstolba:
-		xor ebx,ebx
-		mov bl,cl		; Sector number
+		; Set up registers as for a "Read", and compares against disk size
+setup_regs:
+
+		; Convert a CHS address in P_CX/P_DH into an LBA in eax
+		; CH = cyl[7:0]
+		; CL[0:5] = sector (1-based)  CL[7:6] = cyl[9:8]
+		; DH = head
+		movzx ecx,P_CX
+		movzx ebx,cl		; Sector number
 		and bl,3Fh
-		dec bx
-		mov si,dx
-		mov ax,[Heads]
+		dec ebx			; Sector number is 1-based
+		movzx edi,P_DH		; Head number
+		movzx eax,word [Heads]
 		shr cl,6
 		xchg cl,ch		; Now CX <- cylinder number
-		mul cx			; DX:AX <- AX*CX
-		shr si,8		; SI <- head number
-		add ax,si
-		adc dx,byte 0
-		shl edx,16
-		or eax,edx
+		mul ecx			; eax <- Heads*cyl# (edx <- 0)
+		add eax,edi
 		mul dword [Sectors]
 		add eax,ebx
-		ret
-
-		; Set up registers as for a "Read", and compares against disk size
-setup_regs:
-		call chstolba
-		movzx edi,P_BX		; Get linear address of target buffer
-		movzx ecx,P_ES
-		shr ecx,4
-		add edi,ecx
-		movzx ecx,P_AL
-		lea ebx,[eax+ecx]
+		; Now eax = LBA
+
+		;
+		; setup_regs continues...
+		;
+		; Note: edi[31:16] and ecx[31:16] = 0 already
+		mov di,P_BX		; Get linear address of target buffer
+		mov cx,P_ES
+		shl ecx,4
+		add edi,ecx		; EDI = address to fetch to
+		movzx ecx,P_AL		; Sector count
 		mov esi,eax
-		shr esi,SECTORSIZE_LG2
-		add esi,[DiskBuf]
-		cmp ebx,[DiskSize]
-		jae .overrun
-		shr ecx,SECTORSIZE_LG2-1
+		add eax,ecx
+		shl esi,SECTORSIZE_LG2
+		add esi,[DiskBuf]	; Get address in high memory
+		cmp eax,[DiskSize]	; Check the high mark against limit
+		ja .overrun
+		shl ecx,SECTORSIZE_LG2-1 ; Convert count to 16-bit words
 		ret
 
-.overrun:	pop ax			; Drop return address
+.overrun:	pop ax			; Drop setup_regs return address
 		mov ax,0400h		; Sector not found
 		ret
 
@@ -252,6 +255,10 @@ int15_e820:
 		mov ebx,E820Table
 .renew:
 		add bx, byte 12		; Advance to next
+		mov eax,[bx-4]		; Type
+		and eax,eax		; Null type?
+		jz .renew		; If so advance to next
+		mov [es:di+16],eax
 		mov eax,[bx-12]		; Start addr (low)
 		mov [es:di],eax
 		mov ecx,[bx-8]		; Start addr (high)
@@ -262,8 +269,6 @@ int15_e820:
 		sbb ecx,[bx-8]
 		mov [es:di+8],eax	; Length (low)
 		mov [es:di+12],ecx	; Length (high)
-		mov eax,[bx-4]		; Type
-		mov [es:di+16],eax
 		cmp dword [bx+8], byte -1	; Type of next = end?
 		jne .notdone
 		xor ebx,ebx		; Done with table
@@ -401,6 +406,7 @@ Mover_src1:	db 0, 0, 0		; Low 24 bits of source addy
 		db 93h			; Access rights
 		db 00h			; Extended access rights
 Mover_src2:	db 0			; High 8 bits of source addy
+		dw 0ffffh		; 64 K segment size
 Mover_dst1:	db 0, 0, 0		; Low 24 bits of target addy
 		db 93h			; Access rights
 		db 00h			; Extended access rights
@@ -429,6 +435,9 @@ OldDosMem	dw 0			; Old position of DOS mem end
 DriveNo		db 0			; Our drive number
 DriveType	db 0			; Our drive type (floppies)
 
+MyStack		dw 0			; Offset of stack
+		dw 0			; Padding
+
 		; End patch area
 
 Stack		dd 0			; Saved SS:ESP on invocation
diff --git a/memdisk/setup.c b/memdisk/setup.c
index a2e71fba..d2cec95b 100644
--- a/memdisk/setup.c
+++ b/memdisk/setup.c
@@ -43,6 +43,8 @@ struct patch_area {
 
   uint8_t  driveno;
   uint8_t  drivetype;
+
+  uint16_t mystack;
 };
 
 /* This is the header in the boot sector/setup area */
@@ -105,7 +107,7 @@ rdz_16(uint32_t addr)
   asm volatile("movw %%fs:%1,%0" : "=r" (data) : "m" (*(uint16_t *)addr));
   return data;
 }
-static inline uint8_t
+static inline uint32_t
 rdz_32(uint32_t addr)
 {
   uint32_t data;
@@ -181,6 +183,8 @@ void __attribute__((noreturn)) die(void)
     asm volatile("hlt");
 }
 
+#define STACK_NEEDED	128	/* Number of bytes of stack */
+
 /*
  * Actual setup routine
  * Returns the drive number (which is then passed in %dl to the
@@ -215,8 +219,17 @@ uint32_t setup(void)
 
   geometry = get_disk_image_geometry(shdr->ramdisk_image, shdr->ramdisk_size);
 
+  printf("Disk is %s, %u K, C/H/S = %u/%u/%u\n",
+	 geometry->driveno ? "hard disk" : "floppy",
+	 geometry->sectors >> 1,
+	 geometry->c, geometry->h, geometry->s);
+
+
+  puts("e820map_init ");
   e820map_init();		/* Initialize memory data structure */
+  puts("get_mem ");
   get_mem();			/* Query BIOS for memory map */
+  puts("parse_mem\n");
   parse_mem();			/* Parse memory map */
 
   printf("dos_mem  = %#10x (%u K)\n"
@@ -251,7 +264,7 @@ uint32_t setup(void)
      2 additional ranges plus the terminating range, over what
      nranges currently show. */
 
-  total_size = hptr->total_size + (nranges+3)*12;
+  total_size = hptr->total_size + (nranges+3)*12 + STACK_NEEDED;
   printf("Total size needed = %u bytes\n", total_size);
 
   if ( total_size > dos_mem ) {
@@ -262,10 +275,14 @@ uint32_t setup(void)
   driveraddr  = stddosmem - total_size;
   driveraddr &= ~0x3FF;
 
+  /* Anything beyond the end is for the stack */
+  pptr->mystack = (uint16_t)(stddosmem-driveraddr);
+
   printf("Old dos memory at 0x%05x (map says 0x%05x), loading at 0x%05x\n",
 	 stddosmem, dos_mem, driveraddr);
 
   /* Reserve this range of memory */
+  wrz_16(BIOS_BASEMEM, driveraddr >> 10);
   insertrange(driveraddr, dos_mem-driveraddr, 2);
   parse_mem();
 
@@ -281,8 +298,13 @@ uint32_t setup(void)
   pptr->oldint13 = rdz_32(BIOS_INT13);
   pptr->oldint15 = rdz_32(BIOS_INT15);
 
-  /* Claim the memory and copy the driver into place */
-  wrz_16(BIOS_BASEMEM, dos_mem >> 10);
+  /* Adjust the E820 table: if there are null ranges (type 0)
+     at the end, change them to type end of list (-1).
+     This is necessary for the driver to be able to report end
+     of list correctly. */
+  while ( nranges && ranges[nranges-1].type == 0 ) {
+    ranges[--nranges].type = -1;
+  }
 
   /* Copy driver followed by E820 table */
   asm volatile("pushw %%es ; "
@@ -294,16 +316,23 @@ uint32_t setup(void)
 	       "rep ; movsl %%ds:(%%si), %%es:(%%di) ; "
 	       "popw %%es"
 	       :: "r" (driverseg),
-	       "g" ((uint16_t)((nranges+1)*3)), /* 3 dwords/range */
-	       "g" ((uint16_t)ranges),
+	       "r" ((uint16_t)((nranges+1)*3)), /* 3 dwords/range */
+	       "r" ((uint16_t)ranges),
 	       "c" (bin_size >> 2),
 	       "S" (&_binary_memdisk_bin_start),
-	       "D" (0));
+	       "D" (0)
+	       : "esi", "edi", "ecx");
 
   /* Install the interrupt handlers */
+  printf("old: int13 = %08x  int15 = %08x\n",
+	 rdz_32(BIOS_INT13), rdz_32(BIOS_INT15));
+
   wrz_32(BIOS_INT13, driverptr+hptr->int13_offs);
   wrz_32(BIOS_INT15, driverptr+hptr->int15_offs);
 
+  printf("new: int13 = %08x  int15 = %08x\n",
+	 rdz_32(BIOS_INT13), rdz_32(BIOS_INT15));
+
   /* Reboot into the new "disk" */
   asm volatile("pushw %%es ; "
 	       "xorw %%cx,%%cx ; "
@@ -312,9 +341,9 @@ uint32_t setup(void)
 	       "movw $0x0201,%%ax ; "
 	       "movw $0x7c00,%%bx ; "
 	       "int $0x13 ; "
-	       "setc %0 ; "
-	       "popw %%es"
-	       : "=r" (status), "=a" (exitcode)
+	       "popw %%es ; "
+	       "setc %0 "
+	       : "=rm" (status), "=a" (exitcode)
 	       : "d" ((uint16_t)driveno)
 	       : "ebx", "ecx", "edx", "esi", "edi", "ebp");
 
@@ -323,6 +352,8 @@ uint32_t setup(void)
     die();
   }
   
+  puts("Booting...\n");
+
   /* On return the assembly code will jump to the boot vector */
   return driveno;
 }