Import the "gerbert" kernel I worked on earlier this year.

It's a lot crappier than I remembered it. It's gonna need a lot of work.
2025-07-26 18:37:36 +00:00 · 2018-10-16 11:01:38 +02:00 · 2018-10-16 11:01:38 +02:00 · 9396108034
commit 9396108034
parent f608629704
55 changed files with 4600 additions and 0 deletions
--- a/Kernel/i386.cpp
+++ b/Kernel/i386.cpp
@ -0,0 +1,180 @@
+#include "types.h"
+#include "kmalloc.h"
+#include "VGA.h"
+#include "i386.h"
+#include "Assertions.h"
+#include "Task.h"
+
+struct DescriptorTablePointer {
+    WORD size;
+    void* address;
+} PACKED;
+
+static DescriptorTablePointer s_idtr;
+static DescriptorTablePointer s_gdtr;
+static Descriptor* s_idt;
+static Descriptor* s_gdt;
+
+static WORD s_gdtLength;
+
+WORD allocateGDTEntry()
+{
+    // FIXME: This should not grow indefinitely.
+    ASSERT(s_gdtLength < 256);
+    WORD newGDTEntry = s_gdtLength * 8;
+    s_gdtLength++;
+    return newGDTEntry;
+}
+
+#define EH(i, msg) \
+    static void _exception ## i () \
+    { \
+        vga_set_attr(0x0a); \
+        kprintf(msg"\n"); \
+        DWORD cr0, cr2, cr3, cr4; \
+        asm ("movl %%cr0, %%eax":"=a"(cr0)); \
+        asm ("movl %%cr2, %%eax":"=a"(cr2)); \
+        asm ("movl %%cr3, %%eax":"=a"(cr3)); \
+        asm ("movl %%cr4, %%eax":"=a"(cr4)); \
+        kprintf("CR0=%x CR2=%x CR3=%x CR4=%x\n", cr0, cr2, cr3, cr4); \
+        HANG; \
+    }
+
+EH(0, "Divide error")
+EH(1, "Debug exception")
+EH(2, "Unknown error")
+EH(3, "Breakpoint")
+EH(4, "Overflow")
+EH(5, "Bounds check")
+EH(6, "Invalid opcode")
+EH(7, "Coprocessor not available")
+EH(8, "Double fault")
+EH(9, "Coprocessor segment overrun")
+EH(10, "Invalid TSS")
+EH(11, "Segment not present")
+EH(12, "Stack exception")
+EH(13, "General protection fault")
+EH(14, "Page fault")
+EH(15, "Unknown error")
+EH(16, "Coprocessor error")
+
+static void writeRawGDTEntry(WORD selector, DWORD low, DWORD high)
+{
+    WORD i = (selector & 0xfffc) >> 3;
+    s_gdt[i].low = low;
+    s_gdt[i].high = high;
+
+    if (i > s_gdtLength) {
+        s_gdtr.size = (s_gdtLength + 1) * 8;
+    }
+}
+
+void writeGDTEntry(WORD selector, Descriptor& descriptor)
+{
+    writeRawGDTEntry(selector, descriptor.low, descriptor.high);
+}
+
+Descriptor& getGDTEntry(WORD selector)
+{
+    WORD i = (selector & 0xfffc) >> 3;
+    return *(Descriptor*)(&s_gdt[i]);
+}
+
+void flushGDT()
+{
+    s_gdtr.address = s_gdt;
+    s_gdtr.size = (s_gdtLength * 8) - 1;
+    asm("lgdt %0"::"m"(s_gdtr));
+}
+
+void gdt_init()
+{
+    s_gdt = new Descriptor[256];
+    s_gdtLength = 5;
+
+    s_gdtr.address = s_gdt;
+    s_gdtr.size = (s_gdtLength * 8) - 1;
+
+    writeRawGDTEntry(0x0000, 0x00000000, 0x00000000);
+    writeRawGDTEntry(0x0008, 0x0000ffff, 0x00cf9a00);
+    writeRawGDTEntry(0x0010, 0x0000ffff, 0x00cf9200);
+    writeRawGDTEntry(0x0018, 0x0000ffff, 0x00cffa00);
+    writeRawGDTEntry(0x0020, 0x0000ffff, 0x00cff200);
+
+    flushGDT();
+}
+
+static void unimp_trap()
+{
+    kprintf("Unhandled IRQ.");
+    HANG;
+}
+
+void registerInterruptHandler(BYTE index, void (*f)())
+{
+    s_idt[index].low = 0x00080000 | LSW((f));
+    s_idt[index].high = ((DWORD)(f) & 0xffff0000) | 0x8e00;
+    flushIDT();
+}
+
+void registerUserCallableInterruptHandler(BYTE index, void (*f)())
+{
+    s_idt[index].low = 0x00080000 | LSW((f));
+    s_idt[index].high = ((DWORD)(f) & 0xffff0000) | 0xee00;
+    flushIDT();
+}
+
+void flushIDT()
+{
+    asm("lidt %0"::"m"(s_idtr));
+}
+
+/* If an 8259 gets cranky, it'll generate a spurious IRQ7.
+ * ATM I don't have a clear grasp on when/why this happens,
+ * so I ignore them and assume it makes no difference.
+ */
+
+extern "C" void irq7_handler();
+asm(
+    ".globl irq7_handler \n"
+    "irq7_handler: \n"
+    "   iret\n"
+);
+
+void idt_init()
+{
+    s_idt = new Descriptor[256];
+
+    s_idtr.address = s_idt;
+    s_idtr.size = 0x100 * 8;
+
+    for (BYTE i = 0xff; i > 0x10; --i)
+        registerInterruptHandler(i, unimp_trap);
+
+    registerInterruptHandler(0x00, _exception0);
+    registerInterruptHandler(0x01, _exception1);
+    registerInterruptHandler(0x02, _exception2);
+    registerInterruptHandler(0x03, _exception3);
+    registerInterruptHandler(0x04, _exception4);
+    registerInterruptHandler(0x05, _exception5);
+    registerInterruptHandler(0x06, _exception6);
+    registerInterruptHandler(0x07, _exception7);
+    registerInterruptHandler(0x08, _exception8);
+    registerInterruptHandler(0x09, _exception9);
+    registerInterruptHandler(0x0a, _exception10);
+    registerInterruptHandler(0x0b, _exception11);
+    registerInterruptHandler(0x0c, _exception12);
+    registerInterruptHandler(0x0d, _exception13);
+    registerInterruptHandler(0x0e, _exception14);
+    registerInterruptHandler(0x0f, _exception15);
+    registerInterruptHandler(0x10, _exception16);
+
+    registerInterruptHandler(0x57, irq7_handler);
+
+    flushIDT();
+}
+
+void loadTaskRegister(WORD selector)
+{
+    asm("ltr %0"::"r"(selector));
+}