kernel: add a basic thread scheduler

Add a basic thread scheduler. This should allow the kernel to schedule
threads according to the round robin algorithm.

Signed-off-by: Danny Holman <dholman@gymli.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/arch/i386/kernel/switch_thread.s b/arch/i386/kernel/switch_thread.s
new file mode 100644
index 0000000..f1168d5
--- /dev/null
+++ b/arch/i386/kernel/switch_thread.s
@@ -0,0 +1,28 @@
+.global switch_thread
+.type switch_thread, @function
+switch_thread:
+        pushl %ebp
+        movl %esp, %ebp
+
+        pushl %ebx
+        pushl %esi
+        pushl %edi
+        pushl %ebp
+
+        movl 8(%ebp), %esi
+        movl 12(%ebp), %edi
+
+        movl %esp, (%edi);
+        movl %cr3, %ecx
+        movl %ecx, 4(%edi)
+
+        movl (%esi), %esp
+        movl 4(%esi), %ecx
+        movl %ecx, %cr3
+
+        popl %ebp
+        popl %edi
+        popl %esi
+        popl %ebx
+        popl %ebp
+        ret