From: Matthias Kruk <m@m10k.eu>
Date: Fri, 27 Sep 2019 07:51:46 +0000 (+0900)
Subject: Modify task_switch function so it can be used to switch to new tasks which have not... 
X-Git-Url: https://git.corax.cc/?a=commitdiff_plain;h=ff1e021c7aed7c38e03beda7b416cdc0e8a73015;p=corax

Modify task_switch function so it can be used to switch to new tasks which have not been executed before, but also to return to interrupted tasks
---

diff --git a/kernel/arch/task.S b/kernel/arch/task.S
index a041b72..43f3b12 100644
--- a/kernel/arch/task.S
+++ b/kernel/arch/task.S
@@ -28,6 +28,7 @@
 #define OFFSET_CR3    4
 #define OFFSET_KSTACK 8
 #define OFFSET_PRIVL  12
+#define OFFSET_STATE  16
 
 .extern _cpu
 
@@ -219,7 +220,31 @@ task_switch:
 	/* load new ESP */
 3:	movl	OFFSET_ESP0(%edi), %esp
 
-	/* pretend that we're returning from an interrupt */
+	/*
+	 * If this is a new task, we have to use _int_restore to return,
+	 * but if this task has been executed before, we can simply ret.
+	 * New tasks have state TASK_STATE_NEW, which is zero.
+	 */
+
+	movl	OFFSET_STATE(%edi), %eax
+	test	%eax, %eax
+	jz		4f
+	xorl	%eax, %eax
+
+	/*
+	 * If the context has previously executed, it was interrupted in this
+	 * very same function, so by switching back to its stack and page directory
+	 * we have done enough to restore it's context. Everything else will happen
+	 * when the task returns "naturally" to user-space
+	 */
+	ret
+
+4:	movl	$1, OFFSET_STATE(%edi)
+	/*
+	 * In the previous line, the task state is set to TASK_STATE_RUNNING.
+	 * This is the only place where a transition from NEW to any other state
+	 * should occur (excluding BROKEN)
+	 */
 	jmp		_int_restore
 
 task_get_current:
diff --git a/kernel/include/arch.h b/kernel/include/arch.h
index 7499bae..fec57bb 100644
--- a/kernel/include/arch.h
+++ b/kernel/include/arch.h
@@ -21,10 +21,11 @@
 
 #include <corax/types.h>
 
-#define TASK_STATE_BROKEN  0
+#define TASK_STATE_NEW     0
 #define TASK_STATE_RUNNING 1
 #define TASK_STATE_READY   2
 #define TASK_STATE_WAITING 3
+#define TASK_STATE_BROKEN  4
 
 typedef struct task task_t;
 
@@ -33,11 +34,10 @@ struct task {
 	u32_t t_pgdir;
 	void *t_kstack;
 	u32_t t_privl;
+	u32_t t_state;
 
 	u32_t t_tslice;
 	u32_t t_rslice;
-
-	u32_t t_state;
 } __attribute__((packed));
 
 int     cpu_get_id(void);