From 7d9800f1ebaa1da1804d0ec8b2f739080f276a74 Mon Sep 17 00:00:00 2001
From: shockrah <alejandros714@protonmail.com>
Date: Sun, 13 Oct 2019 23:14:49 -0700
Subject: [PATCH] starting point for interrupt handlers though some of this
 code isn't ready to be used, it serves as a reference point for later

---
 idt.h             |  3 ++
 idt.s             |  7 ++++
 interrupt_entry.s | 96 +++++++++++++++++++++++++++++++++++++++++++++++
 interrupts.c      |  5 +++
 interrupts.h      | 34 +++++++++++++++++
 kernel.c          | 14 +++++++
 kernel.h          |  8 ++++
 7 files changed, 167 insertions(+)
 create mode 100644 idt.h
 create mode 100644 idt.s
 create mode 100644 interrupt_entry.s
 create mode 100644 interrupts.c
 create mode 100644 interrupts.h
 create mode 100644 kernel.c
 create mode 100644 kernel.h

diff --git a/idt.h b/idt.h
new file mode 100644
index 0000000..dd3c685
--- /dev/null
+++ b/idt.h
@@ -0,0 +1,3 @@
+#include "types.h"
+
+void load_idt(void* idt_addr);
diff --git a/idt.s b/idt.s
new file mode 100644
index 0000000..69d0f46
--- /dev/null
+++ b/idt.s
@@ -0,0 +1,7 @@
+global load_idt
+
+load_idt:
+	; takes the address of the first element in the Interrupt descriptor table
+	mov eax, [esp+4]
+	lidt eax
+	ret
diff --git a/interrupt_entry.s b/interrupt_entry.s
new file mode 100644
index 0000000..da7f767
--- /dev/null
+++ b/interrupt_entry.s
@@ -0,0 +1,96 @@
+; Dispatching to our interrupt handler code from assembly because some of this is 
+; enourmous pain in C
+
+; Save the register state
+; call the C handler
+; executes iret(expects the stack to look like struct stack_state)
+
+
+; If the interrupt we need to handle doesn't produce an error code then must provide a 0
+; for consistency
+
+extern interrupt_handler
+
+%macro no_err_handler 1
+global interrupt_handler_%1 	; defined in interrupts.h
+interrupt_handler_%1:
+	push dword 0
+	push dword %1
+	jmp common_int_handler
+%endmacro
+
+; deals with the intterrupts that do give us an error code
+%macro err_code_handler 1
+global interrupt_handler_%1
+interrupt_handler_%1:
+	push dword %1
+	jmp common_int_handler
+%endmacro
+
+common_int_handler:
+	; save thigns before do our C-call
+	push eax
+	push ebx
+	push ecx
+	push edx
+
+	push cs
+	push ds
+	push es 
+	push fs 
+	push gs
+	push ss
+
+	push esi
+	push edi
+	push ebp
+	push esp
+
+	call interrupt_handler
+	; restore state to the function
+	pop eax
+	pop ebx
+	pop ecx
+	pop edx
+
+	pop cs
+	pop ds
+	pop es 
+	pop fs 
+	pop gs
+	pop ss
+
+	pop esi
+	pop edi
+	pop ebp
+	pop esp
+	
+	add esp, 8
+	; special instruction which lets us jump back to code
+	; which was previously interrupted
+	iret 	
+
+
+no_err_handler 1
+no_err_handler 2
+no_err_handler 3
+no_err_handler 4
+no_err_handler 5
+no_err_handler 6
+no_err_handler 7
+
+err_code_handler 8
+
+no_err_handler 9
+
+err_code_handler 10
+err_code_handler 11
+err_code_handler 12
+err_code_handler 13
+err_code_handler 14
+
+no_err_handler 15
+no_err_handler 16
+
+err_code_handler 17
+
diff --git a/interrupts.c b/interrupts.c
new file mode 100644
index 0000000..d12c4d9
--- /dev/null
+++ b/interrupts.c
@@ -0,0 +1,5 @@
+#include "interrupts.h"
+#include "types.h"
+
+void interrupt_handler(struct cpu_reg_state cpu, struct stack_state stack, u32 interrupt_code) {
+}
diff --git a/interrupts.h b/interrupts.h
new file mode 100644
index 0000000..fd27eb2
--- /dev/null
+++ b/interrupts.h
@@ -0,0 +1,34 @@
+#include "types.h"
+
+struct cpu_reg_state {
+	u32 eax;
+	u32 ebx;
+	u32 ecx;
+	u32 edx;
+
+	u16 cs;
+	u16 ds;
+	u16 es; 
+	u16 fs; 
+	u16 gs;
+	u16 ss;
+
+	u32 esi;
+	u32 edi;
+	u32 ebp;
+	u32 eip;
+	u32 esp;
+
+	u32 eflags;
+}__attribute__((packed));
+
+// Populated by the interrupt handler itself
+struct stack_state {
+	u32 error_code; 	// 8 10 11 12 13 14 17 <= ony interrupts that actually use the error code
+	u32 eip;
+	u16 cs;
+	u32 eflags;
+};
+
+
+void interrupt_handler(struct cpu_reg_state, struct stack_state, u32);
diff --git a/kernel.c b/kernel.c
new file mode 100644
index 0000000..0076ed2
--- /dev/null
+++ b/kernel.c
@@ -0,0 +1,14 @@
+#include "kernel.h"
+#include "types.h"
+#include "gdt.h"
+#include "idt.h"
+
+GDT GDT_PTR;
+GDT _GDT[6]; 	// because there are only 6 segments we care about
+
+u32 kinit() {
+	init_segment_selectors(); 	// found in gdt.s
+}
+void kmain() {
+}
+
diff --git a/kernel.h b/kernel.h
new file mode 100644
index 0000000..bf7a4ff
--- /dev/null
+++ b/kernel.h
@@ -0,0 +1,8 @@
+#include "types.h"
+#include "interrupts.h"
+
+
+// handles the main initialization things for the main kernel routine later on
+u32 kinit();
+
+void kmain();