akesterson · January 25, 2015 02:26
diff --git a/gistfile1.txt b/gistfile1.txt
 ##### First we build from scratch ...
 #######################################

 akesterson@akesterson-pc:~/source/upstream/git/akesterson/piquant$ make clean all
 rm -f boot.bin asm/*o src/*o
 bcc -ansi -3 -c -o src/kernel.o src/kernel.c
 ld86 -T0x1000 -M -o kernel.bin src/kernel.o
              kernel          _printString  0  0000101b  R
              kernel                 _main  0  00001049  R
              kernel            _printChar  0  00001000  R
 Total memory used: 00000108
 objdump86 kernel.bin | \
 		grep -E "^[0-9]+ T _.*" | \
 		python -c "import sys; print '\n'.join([\"_extern_c%s:\n    jmp 0x1000:0x%04x\" % (x.split(' ')[2].strip('\n'), int(x.split(' ')[0].lstrip('0'), 16)-0x1000) for x in sys.stdin.readlines()])" > asm/kernel_syms.S
 cd asm && nasm bootloader.S -f bin -o ../boot.bin
 cat boot.bin kernel.bin > boot.img

 #######################################
 #### TL;DR bootloader.S is supposed to load the 
 #### kernel.bin (from kernel.c) off the floppy
 #### and jump to it.
 #######################################

        mov al, 0x1            ; read the remaining 16 tracks                                                                                                                                   
        mov ch, 0x0            ; .... on track 0 ....                                                                                                                                           
        mov cl, 0x2            ; .... starting at sector 2                                                                                                                                      
        mov bx, 0x1000         ; 0x1000 is a standard kernel start location                                                                                                                     
        mov es, bx
        mov bx, 0x0            ; bx = 0, es:bx = 0x1000:0                                                                                                                                       
        call loadFloppyDiskSectors
        ;; ... snip ...
        jmp _extern_c_main

 #######################################
 #### _extern_c_main is constructed from the symbol table of kernel.bin
 #### and contains the (or what should be) the addresses of all functions
 #### built into kernel.bin from kernel.c
 ####
 #### Here's the contents of asm/kernel_syms.S, the Makefile rebuilds it
 #### every time kernel.bin changes:
 #######################################
 _extern_c_main:
    jmp 0x1000:0x0049
 _extern_c_printCh:
    jmp 0x1000:0x0000

 ########################################
 ##### But instead of jumping to main() and looping forever (as expected),
 ##### Bochs reaches what appears to be uninitialized RAM, and I'm not sure
 ##### my code is doing what I expect. Consider:
 #########################################

 bochs -f bochsrc -q
 ( .... snip .. )
 Next at t=0
 (0) [0x0000fffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b         ; ea5be000f0
 <bochs:1> break 0x7c00
 <bochs:2> c
 ( ... snip ... )
 (0) Breakpoint 1, 0x00007c00 in ?? ()
 Next at t=14040381
 ( ... snip ... )

 ####################################################
 #### THe disk load goes as expected, or appears to,
 #### loading the kernel.bin into 0x1000:0000 (es:bx)
 ####################################################

 (0) [0x000000007c16] 0000:7c16 (unk. ctxt): mov al, 0x01              ; b001
 <bochs:11> 
 Next at t=15548283
 (0) [0x000000007c18] 0000:7c18 (unk. ctxt): mov ch, 0x00              ; b500
 <bochs:12> 
 Next at t=15548284
 (0) [0x000000007c1a] 0000:7c1a (unk. ctxt): mov cl, 0x02              ; b102
 <bochs:13> 
 Next at t=15548285
 (0) [0x000000007c1c] 0000:7c1c (unk. ctxt): mov bx, 0x1000            ; bb0010
 <bochs:14> 
 Next at t=15548286
 (0) [0x000000007c1f] 0000:7c1f (unk. ctxt): mov es, bx                ; 8ec3
 <bochs:15> 
 Next at t=15548287
 (0) [0x000000007c21] 0000:7c21 (unk. ctxt): mov bx, 0x0000            ; bb0000
 <bochs:16> 
 Next at t=15548288
 (0) [0x000000007c24] 0000:7c24 (unk. ctxt): call .+24 (0x00007c3f)    ; e81800
 <bochs:17> 
 00015548964i[FDD  ] partial read() on floppy image returns 168/512
 Next at t=17014567
 (0) [0x000000007c27] 0000:7c27 (unk. ctxt): mov dh, 0x01              ; b601

 ######## So let's dump the memory there and check it out...

 <bochs:18> writemem "bum   dump.com   bin" 0x1000 6555 35          00010000 65535

 00000000  01 03 10 10 20 00 00 00  58 00 00 00 00 00 00 00  |.... ...X.......|
 00000010  00 00 00 00 00 00 00 00  58 90 00 00 30 00 00 00  |........X...0...|
 00000020  66 89 e3 67 66 8b 77 02  b4 0e b7 00 b3 07 cd 10  |f..gf.w.........|
 00000030  55 89 e5 57 56 53 5b 5e  5f 5d c3 55 89 e5 57 56  |U..WVS[^_].U..WV|
 00000040  53 eb 18 8b 5d 08 8a 03  0f b6 c0 50 e8 cf ff ff  |S...]......P....|
 00000050  ff 83 c4 04 8b 5d 08 43  89 5d 08 8b 5d 08 8a 03  |.....].C.]..]...|
 00000060  84 c0 75 df 5b 5e 5f 5d  c3 55 89 e5 57 56 53 eb  |..u.[^_].U..WVS.|
 00000070  fe 5b 5e 5f 5d c3 00 00  5f 70 72 69 6e 74 53 74  |.[^_]..._printSt|
 00000080  1b 10 00 00 12 00 00 00  5f 6d 61 69 6e 00 00 00  |........_main...|
 00000090  49 10 00 00 12 00 00 00  5f 70 72 69 6e 74 43 68  |I......._printCh|
 000000a0  00 10 00 00 12 00 00 00  00 00 00 00 00 00 00 00  |................|
 000000b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
 0000ffff

 ######################################################################
 ####### Yep, there's our kernel. So we should jump to main() directly ... right?
 ######################################################################

 (0) [0x000000007c34] 0000:7c34 (unk. ctxt): jmp .+66 (0x00007c78)     ; eb42
 <bochs:24> 
 Next at t=17024678
 (0) [0x000000007c78] 0000:7c78 (unk. ctxt): jmp far 1000:0049         ; ea49000010
 <bochs:25> 
 Next at t=17024679
 (0) [0x000000010049] 1000:0049 (unk. ctxt): mov dh, 0xc0              ; b6c0
 <bochs:26> 
 Next at t=17024680
 (0) [0x00000001004b] 1000:004b (unk. ctxt): push ax                   ; 50
 <bochs:27> 
 Next at t=17024681
 (0) [0x00000001004c] 1000:004c (unk. ctxt): call .-49 (0x0001001e)    ; e8cfff
 <bochs:28> 
 Next at t=17025395
 (0) [0x00000001004f] 1000:004f (unk. ctxt): (invalid)                 ; ffff

 ################################################
 #### What the hell? that was not my main() !!!!
 #### What am I doing wrong?
 ################################################
	##### First we build from scratch ...
	#######################################

	akesterson@akesterson-pc:~/source/upstream/git/akesterson/piquant$ make clean all
	rm -f boot.bin asm/o src/o
	bcc -ansi -3 -c -o src/kernel.o src/kernel.c
	ld86 -T0x1000 -M -o kernel.bin src/kernel.o
	kernel _printString 0 0000101b R
	kernel _main 0 00001049 R
	kernel _printChar 0 00001000 R
	Total memory used: 00000108
	objdump86 kernel.bin \| \
	grep -E "^[0-9]+ T _.*" \| \
	python -c "import sys; print '\n'.join([\"_extern_c%s:\n jmp 0x1000:0x%04x\" % (x.split(' ')[2].strip('\n'), int(x.split(' ')[0].lstrip('0'), 16)-0x1000) for x in sys.stdin.readlines()])" > asm/kernel_syms.S
	cd asm && nasm bootloader.S -f bin -o ../boot.bin
	cat boot.bin kernel.bin > boot.img

	#######################################
	#### TL;DR bootloader.S is supposed to load the
	#### kernel.bin (from kernel.c) off the floppy
	#### and jump to it.
	#######################################

	mov al, 0x1 ; read the remaining 16 tracks
	mov ch, 0x0 ; .... on track 0 ....
	mov cl, 0x2 ; .... starting at sector 2
	mov bx, 0x1000 ; 0x1000 is a standard kernel start location
	mov es, bx
	mov bx, 0x0 ; bx = 0, es:bx = 0x1000:0
	call loadFloppyDiskSectors
	;; ... snip ...
	jmp _extern_c_main

	#######################################
	#### _extern_c_main is constructed from the symbol table of kernel.bin
	#### and contains the (or what should be) the addresses of all functions
	#### built into kernel.bin from kernel.c
	####
	#### Here's the contents of asm/kernel_syms.S, the Makefile rebuilds it
	#### every time kernel.bin changes:
	#######################################
	_extern_c_main:
	jmp 0x1000:0x0049
	_extern_c_printCh:
	jmp 0x1000:0x0000

	########################################
	##### But instead of jumping to main() and looping forever (as expected),
	##### Bochs reaches what appears to be uninitialized RAM, and I'm not sure
	##### my code is doing what I expect. Consider:
	#########################################

	bochs -f bochsrc -q
	( .... snip .. )
	Next at t=0
	(0) [0x0000fffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b ; ea5be000f0
	<bochs:1> break 0x7c00
	<bochs:2> c
	( ... snip ... )
	(0) Breakpoint 1, 0x00007c00 in ?? ()
	Next at t=14040381
	( ... snip ... )

	####################################################
	#### THe disk load goes as expected, or appears to,
	#### loading the kernel.bin into 0x1000:0000 (es:bx)
	####################################################

	(0) [0x000000007c16] 0000:7c16 (unk. ctxt): mov al, 0x01 ; b001
	<bochs:11>
	Next at t=15548283
	(0) [0x000000007c18] 0000:7c18 (unk. ctxt): mov ch, 0x00 ; b500
	<bochs:12>
	Next at t=15548284
	(0) [0x000000007c1a] 0000:7c1a (unk. ctxt): mov cl, 0x02 ; b102
	<bochs:13>
	Next at t=15548285
	(0) [0x000000007c1c] 0000:7c1c (unk. ctxt): mov bx, 0x1000 ; bb0010
	<bochs:14>
	Next at t=15548286
	(0) [0x000000007c1f] 0000:7c1f (unk. ctxt): mov es, bx ; 8ec3
	<bochs:15>
	Next at t=15548287
	(0) [0x000000007c21] 0000:7c21 (unk. ctxt): mov bx, 0x0000 ; bb0000
	<bochs:16>
	Next at t=15548288
	(0) [0x000000007c24] 0000:7c24 (unk. ctxt): call .+24 (0x00007c3f) ; e81800
	<bochs:17>
	00015548964i[FDD ] partial read() on floppy image returns 168/512
	Next at t=17014567
	(0) [0x000000007c27] 0000:7c27 (unk. ctxt): mov dh, 0x01 ; b601

	######## So let's dump the memory there and check it out...

	<bochs:18> writemem "bum dump.com bin" 0x1000 6555 35 00010000 65535

	00000000 01 03 10 10 20 00 00 00 58 00 00 00 00 00 00 00 \|.... ...X.......\|
	00000010 00 00 00 00 00 00 00 00 58 90 00 00 30 00 00 00 \|........X...0...\|
	00000020 66 89 e3 67 66 8b 77 02 b4 0e b7 00 b3 07 cd 10 \|f..gf.w.........\|
	00000030 55 89 e5 57 56 53 5b 5e 5f 5d c3 55 89 e5 57 56 \|U..WVS[^_].U..WV\|
	00000040 53 eb 18 8b 5d 08 8a 03 0f b6 c0 50 e8 cf ff ff \|S...]......P....\|
	00000050 ff 83 c4 04 8b 5d 08 43 89 5d 08 8b 5d 08 8a 03 \|.....].C.]..]...\|
	00000060 84 c0 75 df 5b 5e 5f 5d c3 55 89 e5 57 56 53 eb \|..u.[^_].U..WVS.\|
	00000070 fe 5b 5e 5f 5d c3 00 00 5f 70 72 69 6e 74 53 74 \|.[^_]..._printSt\|
	00000080 1b 10 00 00 12 00 00 00 5f 6d 61 69 6e 00 00 00 \|........_main...\|
	00000090 49 10 00 00 12 00 00 00 5f 70 72 69 6e 74 43 68 \|I......._printCh\|
	000000a0 00 10 00 00 12 00 00 00 00 00 00 00 00 00 00 00 \|................\|
	000000b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \|................\|
	*
	0000ffff

	######################################################################
	####### Yep, there's our kernel. So we should jump to main() directly ... right?
	######################################################################

	(0) [0x000000007c34] 0000:7c34 (unk. ctxt): jmp .+66 (0x00007c78) ; eb42
	<bochs:24>
	Next at t=17024678
	(0) [0x000000007c78] 0000:7c78 (unk. ctxt): jmp far 1000:0049 ; ea49000010
	<bochs:25>
	Next at t=17024679
	(0) [0x000000010049] 1000:0049 (unk. ctxt): mov dh, 0xc0 ; b6c0
	<bochs:26>
	Next at t=17024680
	(0) [0x00000001004b] 1000:004b (unk. ctxt): push ax ; 50
	<bochs:27>
	Next at t=17024681
	(0) [0x00000001004c] 1000:004c (unk. ctxt): call .-49 (0x0001001e) ; e8cfff
	<bochs:28>
	Next at t=17025395
	(0) [0x00000001004f] 1000:004f (unk. ctxt): (invalid) ; ffff

	################################################
	#### What the hell? that was not my main() !!!!
	#### What am I doing wrong?
	################################################