From 50e58765b107c908bf42e875b4c98f0fc4cf3b1b Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Fri, 18 Oct 2019 13:50:42 +0000
Subject: [PATCH] Improve debug rom to catch common exception conditions

---
 Makefile                        |  10 +-
 debug/debug.asm                 | 127 -------------------
 debug/main.asm => rom/debug.asm | 216 ++++++++++++++++++++++----------
 3 files changed, 152 insertions(+), 201 deletions(-)
 delete mode 100644 debug/debug.asm
 rename debug/main.asm => rom/debug.asm (61%)

diff --git a/Makefile b/Makefile
index 5229dd6..2adb2f3 100644
--- a/Makefile
+++ b/Makefile
@@ -18,7 +18,7 @@ QEMU_ARGS += --enable-kvm
 endif
 
 ifdef DEBUG
-ROMS += debug.rom
+ROMS += rom/debug.rom
 NASM_ARGS += -l $(basename $@).lst
 endif
 
@@ -33,15 +33,15 @@ default: fdimage.img
 rdos.bin: kernel/*.asm lib/*.asm
 	$(NASM) $(NASM_ARGS) -o $@ -I kernel kernel/main.asm
 
-debug.rom: debug/*.asm lib/*.asm
-	$(NASM) $(NASM_ARGS) -o $@ -I debug debug/main.asm && utils/fix-rom.sh $@
-
 boot/%.bs: boot/%.asm
 	$(NASM) $(NASM_ARGS) -DFLOPPY=$(FLOPPY) -o $@ $<
 
 programs/%.com: programs/%.asm
 	$(NASM) $(NASM_ARGS) -o $@ $<
 
+rom/%.rom: rom/%.asm
+	$(NASM) $(NASM_ARGS) -o $@ $< && utils/fix-rom.sh $@
+
 fdimage.img: boot/fat.bs $(DISTFILES)
 	mformat -C -i $@ -f $(FLOPPY) -B boot/fat.bs ::
 	mcopy -i $@ $(DISTFILES) ::
@@ -51,7 +51,7 @@ hdimage.img: boot/mbr.bs fdimage.img
 
 clean:
 	find -name '*.lst' -delete
-	rm -f $$(cat .gitignore) programs/*.com boot/*.bs utils/emul
+	rm -f $$(cat .gitignore) programs/*.com boot/*.bs rom/*.rom utils/emul
 
 qemu-floppy: fdimage.img $(ROMS)
 	$(QEMU) $(QEMU_ARGS) -boot c -fda fdimage.img
diff --git a/debug/debug.asm b/debug/debug.asm
deleted file mode 100644
index 05c7910..0000000
--- a/debug/debug.asm
+++ /dev/null
@@ -1,127 +0,0 @@
-; Names for words in debug frame
-; Two characters per word, 14 words total
-debug_frame_names:
-  ; general-purpose registers
-  db "AXCXDXBXSPBPSIDI"
-  ; extra registers
-  db "DSESSSIPCSFL"
-
-; Names for bits in debug_frame+26 (FL/Flags register)
-; One character per bit, 16 bits total
-debug_frame_flags:
-  db "++++ODIT"
-  db "SZ+A+P+C"
-
-; Print a single register from the frame
-; in	SI	frame offset for register
-debug_frame_register_print:
-  mov bx, debug_frame_names
-  mov al, [cs:bx+si] ; first name char load
-  call putc
-  mov al, [cs:bx+si+1] ; second name char load
-  call putc
-  mov al, '='
-  call putc
-  mov ax, [ss:bp+si] ; value load
-  ; prepare call to print_number
-  push bx
-  push cx
-  mov bx, 0x0010
-  mov cx, 3
-  call print_number_padded
-  pop cx
-  pop bx
-  mov al, ' '
-  call putc
-  ret
-
-debug_frame_print:
-  mov si, 0
-  mov cx, 8
-.reg1loop:
-  call debug_frame_register_print
-  add si, 2
-  loop .reg1loop
-
-  mov dx, [ss:bp+26]
-  mov di, debug_frame_flags
-  mov cx, 0x0010
-.flag_loop:
-  mov al, [cs:di]
-  inc di
-  cmp al, '+'
-  je .next
-  test dx, 0x8000
-  jnz .write
-  mov al, '-'
-.write:
-  call putc
-.next:
-  sal dx, 1
-  loop .flag_loop
-
-  call printf
-  db 0x0A, 0x0D, 0
-
-  mov si, 16
-  mov cx, 3
-.reg2loop:
-  call debug_frame_register_print
-  add si, 2
-  loop .reg2loop
-
-  mov ax, [bp+24]
-  mov bx, 0x0010
-  mov cx, 3
-  call print_number_padded
-
-  mov al, ':'
-  call putc
-
-  mov ax, [bp+22]
-  mov bx, 0x0010
-  mov cx, 3
-  call print_number_padded
-
-  call printf
-  db 0x0A, 0x0D, 0
-
-  ret
-
-; this prints registers
-; expect to be called as interrupt routine
-isr_debug:
-  push ss
-  push es
-  push ds
-  push di
-  push si
-  push bp
-  push sp
-  push bx
-  push dx
-  push cx
-  push ax
-
-  mov bp, sp
-  mov [bp+08], bp
-  add WORD [bp+08], 28
-
-  call printf
-  db 0x0A, 0x0D, 0
-
-  call debug_frame_print
-
-  pop ax
-  pop cx
-  pop dx
-  pop bx
-  add sp, 2 ; ignore SP
-  pop bp
-  pop bp
-  pop si
-  pop di
-  pop ds
-  pop es
-  add sp, 2 ; ignore SS
-  iret
diff --git a/debug/main.asm b/rom/debug.asm
similarity index 61%
rename from debug/main.asm
rename to rom/debug.asm
index 5ca7610..68b4737 100644
--- a/debug/main.asm
+++ b/rom/debug.asm
@@ -1,19 +1,49 @@
 cpu 8086
 org 0x0000
+
+%macro push8086 0
+  push ss
+  push es
+  push ds
+  push di
+  push si
+  push bp
+  push sp
+  push bx
+  push dx
+  push cx
+  push ax
+
+  ; adjust stored SP to be value before interrupt
+  mov bp, sp
+  mov [bp+08], bp
+  add WORD [bp+08], 28
+%endmacro
+
+%macro pop8086 0
+  pop ax
+  pop cx
+  pop dx
+  pop bx
+  add sp, 2 ; skip SP
+  pop bp
+  pop si
+  pop di
+  pop ds
+  pop es
+  add sp, 2 ; skip SS
+%endmacro
+
 rom:
   db 0x55, 0xAA
 .sectors:
   db 0x00
 .init:
-  mov dx, isr_debug
-  mov al, 0x1
-  call intr_register
-  mov al, 0x03
-  call intr_register
-  retf
+  jmp init
+  nop
 
 .name:
-  db "rDebug", 0
+  db "RDOS debug rom", 0
 
   times (0x18 - ($-$$)) db 0
 .pcir_ptr:
@@ -44,6 +74,48 @@ pnp:
   dw 0 ; reserved
   dw 0
 
+init:
+  mov bx, 0
+  mov dx, isr_divide_error
+  call hook_int
+
+  mov bx, 1
+  mov dx, isr_singlestep
+  call hook_int
+
+  mov bx, 2
+  mov dx, isr_nmi
+  call hook_int
+
+  mov bx, 3
+  mov dx, isr_breakpoint
+  call hook_int
+
+  mov bx, 4
+  mov dx, isr_overflow
+  call hook_int
+
+  ; 5 left out
+
+  mov bx, 6
+  mov dx, isr_invalid_opcode
+  call hook_int
+  retf
+
+; Hook interrupt
+hook_int:
+  ; bx times 4
+  add bx, bx
+  add bx, bx
+  ; store offset
+  mov [bx], dx
+  ; store segment
+  push ax
+  mov ax, cs
+  mov [bx+2], ax
+  pop ax
+  ret
+
 putc:
   push bx
   push cx
@@ -54,26 +126,6 @@ putc:
   pop bx
   ret
 
-intr_register:
-  ; DI = AL * 4
-  mov ah, 4
-  mul ah
-  mov di, ax
-
-  ; ES = 0
-  xor ax, ax
-  mov es, ax
-
-  ; store offset
-  mov ax, dx
-  stosw
-
-  ; store segment
-  mov ax, cs
-  stosw
-
-  ret
-
 ; Names for words in debug frame
 ; Two characters per word, 14 words total
 debug_frame_names:
@@ -140,67 +192,93 @@ debug_frame_print:
   db 0x0A, 0x0D, 0
 
   mov si, 16
-  mov cx, 3
+  mov cx, 5
 .reg2loop:
   call debug_frame_register_print
   add si, 2
   loop .reg2loop
 
-  mov ax, [bp+24]
-  mov bx, 0x0010
-  mov cx, 3
-  call print_number_padded
-
-  mov al, ':'
-  call putc
-
-  mov ax, [bp+22]
-  mov bx, 0x0010
-  mov cx, 3
-  call print_number_padded
-
   call printf
   db 0x0A, 0x0D, 0
 
   ret
 
-; this prints registers
-; expect to be called as interrupt routine
-isr_debug:
-  push ss
-  push es
-  push ds
-  push di
-  push si
-  push bp
-  push sp
-  push bx
-  push dx
-  push cx
-  push ax
+isr_divide_error:
+  push8086
 
-  mov bp, sp
-  mov [bp+08], bp
-  add WORD [bp+08], 28
+  call printf
+  db 0x0A, 0x0D, "INT 0 - DIVIDE ERROR", 0x0A, 0x0D, 0
+
+  call debug_frame_print
+
+  jmp halt
+
+isr_singlestep:
+  push8086
 
   call printf
   db 0x0A, 0x0D, 0
 
   call debug_frame_print
 
-  pop ax
-  pop cx
-  pop dx
-  pop bx
-  pop bp
-  pop bp
-  pop si
-  pop di
-  pop ds
-  pop es
-  pop ss
+  ; wait for keypress
+  xor ax, ax
+  int 0x16
+
+  ; enable trace flag so we fire again after next instruction
+  or word [ss:bp+26], 0x0100
+
+  pop8086
   iret
 
+isr_nmi:
+  push8086
+
+  call printf
+  db 0x0A, 0x0D, "INT 2 - NON-MASKABLE INTERRUPT", 0x0A, 0x0D, 0
+
+  call debug_frame_print
+
+  jmp halt
+
+isr_breakpoint:
+  push8086
+
+  call printf
+  db 0x0A, 0x0D, 0
+
+  call debug_frame_print
+
+  pop8086
+  iret
+
+isr_overflow:
+  push8086
+
+  call printf
+  db 0x0A, 0x0D, "INT 4 - OVERFLOW", 0x0A, 0x0D, 0
+
+  call debug_frame_print
+
+  jmp halt
+
+isr_invalid_opcode:
+  push8086
+
+  call printf
+  db 0x0A, 0x0D, "INT 6 - INVALID OPCODE", 0x0A, 0x0D, 0
+
+  call debug_frame_print
+
+  jmp halt
+
+halt:
+  call printf
+  db "HALTED", 0x0A, 0x0D, 0
+.loop:
+  hlt
+  jmp halt
+
 %include "printf.asm"
 
 align 512