From 603a8064a3c851ea52adbbd3b5fafe9a2ffa470b Mon Sep 17 00:00:00 2001
From: Mark <alnyan@airmail.cc>
Date: Thu, 30 Jan 2020 12:07:15 +0200
Subject: [PATCH] Thread timer-based preemption

---
 sys/amd64/hw/irq0.S | 21 +++++++++++++++++++++
 sys/sched.c         |  4 ++++
 2 files changed, 25 insertions(+)

diff --git a/sys/amd64/hw/irq0.S b/sys/amd64/hw/irq0.S
index 909a96f..a176cce 100644
--- a/sys/amd64/hw/irq0.S
+++ b/sys/amd64/hw/irq0.S
@@ -17,9 +17,30 @@ _msg0: .string "CPU stopped!\n"
 
 amd64_irq0:
     cli
+
+    // Push caller-saved registers so it appears as if a thread just called yield()
+    pushq %r11
+    pushq %r10
+    pushq %r9
+    pushq %r8
+    pushq %rcx
+    pushq %rdx
+    pushq %rsi
+    pushq %rdi
     pushq %rax
     irq_eoi_lapic 0
+
+    call yield
+
     popq %rax
+    popq %rdi
+    popq %rsi
+    popq %rdx
+    popq %rcx
+    popq %r8
+    popq %r9
+    popq %r10
+    popq %r11
     iretq
 
 amd64_irq2_counting:
diff --git a/sys/sched.c b/sys/sched.c
index c2d3b00..3c05c91 100644
--- a/sys/sched.c
+++ b/sys/sched.c
@@ -1,4 +1,6 @@
 #include "sys/amd64/mm/phys.h"
+#include "sys/amd64/hw/irq.h"
+#include "sys/amd64/hw/idt.h"
 #include "sys/assert.h"
 #include "sys/thread.h"
 #include "sys/mm.h"
@@ -164,5 +166,7 @@ void sched_init(void) {
 }
 
 void sched_enter(void) {
+    extern void amd64_irq0(void);
+    amd64_idt_set(0, 32, (uintptr_t) amd64_irq0, 0x08, IDT_FLG_P | IDT_FLG_R0 | IDT_FLG_INT32);
     context_switch_first(&sched_threads[0]);
 }