Fixed & Improved Makefile, Made V86 GPF handler not directly dereference

a null pointer - due to optimization breaking.

Makefile

@@ -1,17 +1,20 @@
-#TODO make the makefile use targets instead of this mess
+objects = entry.o kernel.o handler.o interrupt.o v86.o print.o
-all:
+CFLAGS = -target "i686-elf" -m32 -ffreestanding -march=pentium-m -fno-stack-protector -nostdlib -c
+
+%.o: %.nasm
+	nasm -f elf32 -o $@ $<
+
+%.o: %.c
+	clang $(CFLAGS) -O2 $<
+
+all: $(objects)
 	nasm boot.nasm -o boot.bin
-	nasm -f elf32 -o entry.o entry.nasm
-	nasm -f elf32 -o handler.o handler.nasm
-	nasm -f elf32 -o v86.o v86.nasm
-	clang -target "i686-elf" -ffreestanding -m32 -O2 -march=pentium-m -fno-stack-protector -nostdlib -c kernel.c
-	clang -target "i686-elf" -ffreestanding -m32 -O2 -mgeneral-regs-only -march=pentium-m -fno-stack-protector -nostdlib -c print.c
 	# not sure why but if interrupt.c has any optimization everything just breaks immediately
-	clang -target "i686-elf" -ffreestanding -m32 -mgeneral-regs-only -march=pentium-m -fno-stack-protector -nostdlib -c interrupt.c
+	gcc -Tlink.ld -m32 -ffreestanding -nostartfiles -nostdlib -o kernel.bin\
-	#clang -target "i686-elf" -ffreestanding -m32 -mgeneral-regs-only -march=i386 -fno-stack-protector -nostdlib -c -o kernel.o kernel.c
+		$(objects)
-	gcc -Tlink.ld -m32 -ffreestanding -nostartfiles -nostdlib -o kernel.bin entry.o v86.o handler.o kernel.o print.o interrupt.o
 	dd bs=256 count=1 conv=notrunc if=boot.bin of=virtdisk.bin
 	dd bs=512 seek=1 conv=notrunc if=kernel.bin of=virtdisk.bin
 virtdisk:
 	dd bs=1M count=32 if=/dev/zero of=virtdisk.bin
 	echo -n -e '\x55\xaa' | dd bs=1 seek=510 conv=notrunc of=virtdisk.bin
+

entry.nasm

@@ -93,6 +93,9 @@ ret
 
 extern tss_data
 
+global ivt
+ivt: dd 0x00000000
+
 gdt_desc:
     dw gdt_end - gdt
     dd gdt

interrupt.c

@@ -66,18 +66,20 @@ void IRQ_clear_mask(char IRQline) {
 }
 
 char v86_if = 0;
+extern uint16_t *ivt;
 extern void real_test();
+__attribute((__no_caller_saved_registers__))
 extern void kbd_wait();
+extern void jmp_usermode_test();
 #define VALID_FLAGS 0xDFF
 __attribute__ ((interrupt))
 void gpf_handler_v86(struct interrupt_frame *frame, unsigned long error_code) {
     asm volatile("mov %%ax,%%ds"::"a"(0x10));
     uint8_t *ip;
-    uint16_t *stack, *ivt;
+    uint16_t *stack;
     uint32_t *stack32;
     char is_operand32 = 0, is_address32 = 0;
-    ip = (size_t)(((frame->cs << 4) + frame->eip) & 0xFFFFF);
+    ip = (uint8_t*)(size_t)(((frame->cs << 4) + frame->eip) & 0xFFFFF);
-    ivt = (uint16_t*)0x0000;
     stack = FP_TO_LINEAR(frame->ss, frame->esp);
     stack32 = (uint32_t*)stack;
 
@@ -156,37 +158,28 @@ void gpf_handler_v86(struct interrupt_frame *frame, unsigned long error_code) {
                 goto done;
             case 0xCD: // INT n
                 vga[0] = 'I'; vga[2]++; if (vga[2] < '0') vga[2] = '0';
-                asm volatile("nop\nnop");
                 switch (ip[1]) {
-                    case 0x30: // Exit V86 Mode?
+                    case 0x30:
-                        asm volatile("nop\nnop");
+                        asm("jmp jmp_usermode_test");
-                        asm volatile("jmp jmp_usermode_test");
+                        for(;;);
-                        //__builtin_unreachable();
+                    case 0x3:
-                        break;
-                    //case 0x20: // ???
-                    //case 0x21: // ???
-                    case 0x3:  // Debugger trap
                         kbd_wait();
-                        asm volatile("nop");
                     default:
-                        stack -= 3;
+                        stack = &stack[-3];
                         frame->esp = ((frame->esp & 0xffff) - 6) & 0xffff;
 
                         stack[0] = (uint16_t) (frame->eip + 2);
                         stack[1] = frame->cs;
                         stack[2] = (uint16_t) frame->eflags;
                         
-                        if (v86_if)
+                        //if (v86_if)
-                            stack[2] |= EFLAG_IF;
+                        //    stack[2] |= EFLAG_IF;
-                        else
+                        //else
-                            stack[2] &= ~EFLAG_IF;
+                        //    stack[2] &= ~EFLAG_IF;
 
                         frame->cs = ivt[ip[1] * 2 + 1];
                         frame->eip = ivt[ip[1] * 2];
-                        asm volatile("nop");
+                        break;
-                        //frame->cs = 0;
-                        //frame->eip = real_test;
-                        goto done;
                 }
                 goto done;
             case 0xCF: // IRET
@@ -206,7 +199,6 @@ void gpf_handler_v86(struct interrupt_frame *frame, unsigned long error_code) {
                 goto done;
             default:
                 for(;;);
-                goto done;
         }
     }
     done:

kernel.c

@@ -98,6 +98,7 @@ void start() {
     if (!sse) return;
     enable_sse();
 
+    // edit
     setup_interrupts();
     setup_tss();
     print_flags();

print.c

@@ -1,20 +1,24 @@
 #include "print.h"
 
 __attribute((__always_inline__))
+__attribute((__no_caller_saved_registers__))
 char nibbleToHex(uint8_t n) {
     return n > 9 ? (n - 10) + 'A' : n + '0';
 }
 __attribute((__always_inline__))
+__attribute((__no_caller_saved_registers__))
 void printByte(uint8_t v, uint16_t *buff) {
     *(char *)&buff[0] = nibbleToHex((v >> 4) & 0xF);
     *(char *)&buff[1] = nibbleToHex(v & 0xF);
 }
 __attribute((__always_inline__))
+__attribute((__no_caller_saved_registers__))
 void printWord(uint16_t v, uint16_t *buff) {
     printByte(v >> 8, buff);
     printByte(v, &buff[2]);
 }
 __attribute((__always_inline__))
+__attribute((__no_caller_saved_registers__))
 void printDword(uint32_t v, uint16_t *buff) {
     printWord(v >> 16, buff);
     printWord(v, &buff[4]);

print.h

@@ -1,6 +1,9 @@
 #pragma once
 #include <stdint.h>
 
+__attribute((__no_caller_saved_registers__))
 void printByte(uint8_t v, uint16_t *buff);
+__attribute((__no_caller_saved_registers__))
 void printWord(uint16_t v, uint16_t *buff);
+__attribute((__no_caller_saved_registers__))
 void printDword(uint32_t v, uint16_t *buff);

v86.nasm

@@ -54,6 +54,7 @@ inc byte [0]
 ;mov ax, 0x6666
 ;mov sp, ax
 int 3
+int 3
 ;jmp .loop
 mov ax, 0x13
 int 0x10