From 75ec633805db108bfddb6454ff7f8d812475feaf Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Mon, 11 Apr 2022 23:29:30 +0200
Subject: kernel: implement `cpu_pause()` in assembly, remove
 `irq_interrupt_flag()`

---
 src/kernel/arch/generic.h             | 3 +++
 src/kernel/arch/i386/boot.s           | 9 +++++++++
 src/kernel/arch/i386/interrupts/irq.c | 5 -----
 src/kernel/arch/i386/interrupts/irq.h | 2 --
 src/kernel/arch/i386/sysenter.c       | 3 ---
 src/kernel/arch/i386/sysenter.s       | 2 ++
 src/kernel/proc.c                     | 7 +++----
 7 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/src/kernel/arch/generic.h b/src/kernel/arch/generic.h
index fcc228e..01a3826 100644
--- a/src/kernel/arch/generic.h
+++ b/src/kernel/arch/generic.h
@@ -18,6 +18,9 @@ void halt_cpu(void);
 __attribute__((noreturn))
 void cpu_shutdown(void);
 
+/** on x86: waits for an IRQ */
+void cpu_pause(void);
+
 // src/arch/i386/sysenter.s
 _Noreturn void sysexit(struct registers);
 
diff --git a/src/kernel/arch/i386/boot.s b/src/kernel/arch/i386/boot.s
index ea31aa1..24c076f 100644
--- a/src/kernel/arch/i386/boot.s
+++ b/src/kernel/arch/i386/boot.s
@@ -23,3 +23,12 @@ halt_cpu:
 	cli
 1:	hlt
 	jmp 1b
+
+
+.global cpu_pause
+.type cpu_pause, @function
+cpu_pause:
+	sti
+	hlt
+	cli
+	ret
diff --git a/src/kernel/arch/i386/interrupts/irq.c b/src/kernel/arch/i386/interrupts/irq.c
index 7b8c166..5918169 100644
--- a/src/kernel/arch/i386/interrupts/irq.c
+++ b/src/kernel/arch/i386/interrupts/irq.c
@@ -31,8 +31,3 @@ void irq_eoi(uint8_t line) {
 	if (line >= 8)
 		port_out8(PIC2, 0x20);
 }
-
-void irq_interrupt_flag(bool flag) {
-	if (flag)	asm("sti" : : : "memory");
-	else		asm("cli" : : : "memory");
-}
diff --git a/src/kernel/arch/i386/interrupts/irq.h b/src/kernel/arch/i386/interrupts/irq.h
index 73d4af2..f523154 100644
--- a/src/kernel/arch/i386/interrupts/irq.h
+++ b/src/kernel/arch/i386/interrupts/irq.h
@@ -4,5 +4,3 @@
 
 void irq_init(void);
 void irq_eoi(uint8_t line);
-
-void irq_interrupt_flag(bool flag);
diff --git a/src/kernel/arch/i386/sysenter.c b/src/kernel/arch/i386/sysenter.c
index 1aee254..5712ee3 100644
--- a/src/kernel/arch/i386/sysenter.c
+++ b/src/kernel/arch/i386/sysenter.c
@@ -1,5 +1,4 @@
 #include <kernel/arch/generic.h>
-#include <kernel/arch/i386/interrupts/irq.h>
 #include <kernel/arch/i386/sysenter.h>
 #include <kernel/proc.h>
 #include <shared/syscalls.h>
@@ -22,8 +21,6 @@ _Noreturn void sysenter_stage2(void) {
 	regs->esp = (userptr_t) regs->ecx; // fix them up
 	regs->eip = (userptr_t) regs->edx;
 
-	irq_interrupt_flag(false);
-
 	val = _syscall(regs->eax, regs->ebx,
 	               regs->esi, regs->edi, (uintptr_t)regs->ebp);
 	if (process_current->state == PS_RUNNING) { // TODO move to _syscall()
diff --git a/src/kernel/arch/i386/sysenter.s b/src/kernel/arch/i386/sysenter.s
index db65a8c..ade69ec 100644
--- a/src/kernel/arch/i386/sysenter.s
+++ b/src/kernel/arch/i386/sysenter.s
@@ -48,6 +48,8 @@ sysenter_setup:
 	ret
 
 sysenter_stage1:
+	cli /* prevent random IRQs in the middle of kernel code */
+
 	//   disable paging
 	// I don't want to damage any of the registers passed in by the user,
 	// so i'm using ESP as a temporary register. At this point there's nothing
diff --git a/src/kernel/proc.c b/src/kernel/proc.c
index 1f012fa..944f5b9 100644
--- a/src/kernel/proc.c
+++ b/src/kernel/proc.c
@@ -6,7 +6,6 @@
 #include <kernel/vfs/mount.h>
 #include <shared/mem.h>
 #include <stdint.h>
-#include <kernel/arch/i386/interrupts/irq.h> // TODO move irq stuff to arch/generic
 #include <kernel/vfs/root.h> // TODO
 
 struct process *process_first;
@@ -86,13 +85,13 @@ _Noreturn void process_idle(void) {
 	for (;;) {
 		for (size_t i = 0; i < len; i++) {
 			if (procs[i]->waits4irq.ready()) {
+				/* if this is entered during the first iteration, it indicates a
+				 * kernel bug. this should be logged. TODO? */
 				vfs_root_handler(&procs[i]->waits4irq.req); // TODO this should be a function pointer too
 				process_switch_any();
 			}
 		}
-		irq_interrupt_flag(true);
-		asm("hlt" ::: "memory"); // TODO move to irq.c
-		irq_interrupt_flag(false);
+		cpu_pause();
 	}
 }
 
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