From 03f2b2b4c9dcfc6d88d95f2c9e6a8b806d5e578e Mon Sep 17 00:00:00 2001
From: Dan Cross <cross@gajendra.net>
Date: Wed, 23 Aug 2023 20:05:47 +0000
Subject: [PATCH] proc: add Label and swtch

Add a `Label` structure that encapsulates kernel thread
register state, and a `swtch` to jump between threads (as
defined by labels).

Signed-off-by: Dan Cross <cross@gajendra.net>
---
 x86_64/src/dat.rs  |  1 +
 x86_64/src/main.rs | 28 ++++++++++++++++++++++++++
 x86_64/src/proc.rs | 50 ++++++++++++++++++++++++++++++++++++++++++++++
 xtask/src/main.rs  |  1 +
 4 files changed, 80 insertions(+)
 create mode 100644 x86_64/src/dat.rs
 create mode 100644 x86_64/src/proc.rs

diff --git a/x86_64/src/dat.rs b/x86_64/src/dat.rs
new file mode 100644
index 0000000..ab0c014
--- /dev/null
+++ b/x86_64/src/dat.rs
@@ -0,0 +1 @@
+//
\ No newline at end of file
diff --git a/x86_64/src/main.rs b/x86_64/src/main.rs
index db7f7ec..f0a312a 100644
--- a/x86_64/src/main.rs
+++ b/x86_64/src/main.rs
@@ -1,25 +1,53 @@
 #![feature(alloc_error_handler)]
 #![feature(asm_const)]
+#![feature(naked_functions)]
 #![cfg_attr(not(any(test, feature = "cargo-clippy")), no_std)]
 #![cfg_attr(not(test), no_main)]
 #![allow(clippy::upper_case_acronyms)]
 #![forbid(unsafe_op_in_unsafe_fn)]
 
+mod dat;
 mod devcons;
 mod pio;
+mod proc;
 mod uart16550;
 
+use proc::{swtch, Label};
+
 #[cfg(not(test))]
 core::arch::global_asm!(include_str!("l.S"), options(att_syntax));
 
 use port::println;
 
+static mut THRSTACK: [u64; 1024] = [0; 1024];
+static mut CTX: u64 = 0;
+static mut THR: u64 = 0;
+
+fn jumpback() {
+    println!("in a thread");
+    unsafe {
+        let thr = &mut *(THR as *mut Label);
+        let ctx = &mut *(CTX as *mut Label);
+        swtch(thr, ctx);
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn main9() {
     devcons::init();
     println!();
     println!("r9 from the Internet");
     println!("looping now");
+    let mut ctx = Label::new();
+    let mut thr = Label::new();
+    thr.pc = jumpback as u64;
+    unsafe {
+        thr.sp = &mut THRSTACK[1023] as *mut _ as u64;
+        CTX = &mut ctx as *mut _ as u64;
+        THR = &mut thr as *mut _ as u64;
+        swtch(&mut ctx, &mut thr);
+    }
+    println!("came out the other side of a context switch");
     #[allow(clippy::empty_loop)]
     loop {}
 }
diff --git a/x86_64/src/proc.rs b/x86_64/src/proc.rs
new file mode 100644
index 0000000..6d5d204
--- /dev/null
+++ b/x86_64/src/proc.rs
@@ -0,0 +1,50 @@
+use core::arch::asm;
+
+#[repr(C)]
+pub struct Label {
+    pub pc: u64,
+    pub sp: u64,
+    pub fp: u64,
+    rbx: u64,
+    r12: u64,
+    r13: u64,
+    r14: u64,
+    r15: u64,
+}
+
+impl Label {
+    pub const fn new() -> Label {
+        Label { pc: 0, sp: 0, fp: 0, rbx: 0, r12: 0, r13: 0, r14: 0, r15: 0 }
+    }
+}
+
+#[naked]
+pub unsafe extern "C" fn swtch(save: &mut Label, next: &mut Label) {
+    unsafe {
+        asm!(
+            r#"
+            movq (%rsp), %rax
+            movq %rax, 0(%rdi)
+            movq %rsp, 8(%rdi)
+            movq %rbp, 16(%rdi)
+            movq %rbx, 24(%rdi)
+            movq %r12, 32(%rdi)
+            movq %r13, 40(%rdi)
+            movq %r14, 48(%rdi)
+            movq %r15, 56(%rdi)
+
+            movq 0(%rsi), %rax
+            movq 8(%rsi), %rsp
+            movq 16(%rsi), %rbp
+            movq 24(%rsi), %rbx
+            movq 32(%rsi), %r12
+            movq 40(%rsi), %r13
+            movq 48(%rsi), %r14
+            movq 56(%rsi), %r15
+            movq %rax, (%rsp)
+            xorl %eax, %eax
+            ret"#,
+            options(att_syntax, noreturn)
+        );
+    }
+}
diff --git a/xtask/src/main.rs b/xtask/src/main.rs
index b8442d9..a241593 100644
--- a/xtask/src/main.rs
+++ b/xtask/src/main.rs
@@ -517,6 +517,7 @@ fn run(build_params: &BuildParams) -> Result<()> {
             cmd.arg("qemu64,pdpe1gb,xsaveopt,fsgsbase,apic,msr");
             cmd.arg("-smp");
             cmd.arg("8");
+            cmd.arg("-s");
             cmd.arg("-m");
             cmd.arg("8192");
             if build_params.wait_for_gdb {