Split hart0_boot in half, so stacks can be switched in the middle.

2 files changed, 71 insertions, 23 deletions

diff --git a/boards/qemu-virt/qemu-virt.s b/boards/qemu-virt/qemu-virt.s
index 0d69d4d..bd32676 100644
--- a/boards/qemu-virt/qemu-virt.s
+++ b/boards/qemu-virt/qemu-virt.s
@@ -1,5 +1,5 @@
-.extern main
-.extern CONSOLE_STRICT_FLUSH
+.extern hart0_boot
+.extern hart0_early_boot
 
 .section .text.start
 
@@ -11,18 +11,6 @@ _start:
 	csrr tp, mhartid
 	bnez tp, wait_for_hart0
 
-	## Set up hart0's stack.
-	la sp, hart0_initial_stack_top
-
-	## Write a canary to hart0's stack.
-	li t0, 0xdead0bad0defaced
-	la t1, hart0_initial_stack
-	sd t0, (t1)
-
-	## Put the address of the DeviceTree into the first argument position
-	## for hart0_boot.
-	c.mv a0, a1
-
 ### Set up trap handling.
 
 	## Set MENVCFG.STCE, to enable the Sstc extension, which will allow us
@@ -55,9 +43,9 @@ _start:
 	li t0, 0b01 << 11
 	csrs mstatus, t0
 
-	## Next, set MEPC to the address of hart0_boot, so that when we execute
-	## mret, execution will continue there.
-	la t0, hart0_boot
+	## Next, set MEPC to the address of hart0_full_boot, so that when we
+	## execute mret, execution will continue there.
+	la t0, hart0_full_boot
 	csrw mepc, t0
 
 	## Set SATP.MODE to Bare, and clear the rest of the bits. This disables
@@ -78,6 +66,34 @@ _start:
 
 .section .text
 
+.type hart0_full_boot, STT_FUNC
+hart0_full_boot:
+	## Set up hart0's stack.
+	la sp, hart0_initial_stack_top
+
+	## Write a canary to hart0's stack.
+	li t0, 0xdead0bad0defaced
+	la t1, hart0_initial_stack
+	sd t0, (t1)
+
+	## Call hart0_early_boot, passing it the DeviceTree we received and
+	## getting back the address of a stack to switch to.
+	mv a0, a1
+	call hart0_early_boot
+
+	## Switch to the returned stack.
+	mv sp, a0
+
+	## Load the canary back from hart0's stack.
+	la t0, hart0_initial_stack
+	ld a0, (t0)
+
+	## Jump to hart0_boot.
+	j hart0_boot
+.size hart0_full_boot, . - hart0_full_boot
+
+.section .text
+
 .type wait_for_hart0, STT_FUNC
 wait_for_hart0:
 	# TODO
diff --git a/crates/kernel/src/lib.rs b/crates/kernel/src/lib.rs
index 6e09d2b..c0da3bf 100644
--- a/crates/kernel/src/lib.rs
+++ b/crates/kernel/src/lib.rs
@@ -15,18 +15,26 @@ mod panic;
 pub mod arch;
 pub mod logger;
 
-/// The entrypoint to the kernel. This should be executed by hart0 alone. It performs some early
-/// boot tasks, then wakes up any other harts.
+/// The first stage of booting the kernel. This should be executed by hart0 alone. It runs with
+/// paging disabled, and:
+///
+/// - sets up a physical memory allocator
+/// - sets up paging
+/// - allocates some global structures in the higher half of memory:
+///   - a logger's buffer
+///   - a stack for this kernel thread
+///   - the DeviceTree in tree form
+///
+/// It returns the top address of the stack for this kernel thread.
 ///
 /// # Safety
 ///
 /// - The `device_tree` pointer must be a valid pointer into physical memory. See
 ///   `device_tree::FlattenedDeviceTree::from_ptr` for the precise requirements.
-/// - This must be called in supervisor mode with paging and traps disabled, but with all traps
-///   delegated to supervisor mode.
-/// - Any other harts must not be running concurrently with us. TODO: Define their state.
+/// - This must be called in supervisor mode with paging disabled.
+/// - Any other harts must not be running concurrently with us.
 #[no_mangle]
-pub unsafe extern "C" fn hart0_boot(device_tree: *const u8) -> ! {
+pub unsafe extern "C" fn hart0_early_boot(device_tree: *const u8) -> ! {
     // Set up the logger.
     logger::init();
 
@@ -79,6 +87,25 @@ pub unsafe extern "C" fn hart0_boot(device_tree: *const u8) -> ! {
             .expect("failed to configure the buddy allocator");
     dbg!(alloc_buddy.debug_free_lists());
 
+    todo!()
+}
+
+/// The entrypoint to the kernel, to be run after paging is set up. This should be executed by
+/// hart0 alone. It performs some early boot tasks, then wakes up any other harts.
+///
+/// It receives the stack canary from the initial stack, and validates it.
+///
+/// # Safety
+///
+/// - `hart0_early_boot` must have been called.
+/// - This must be called in supervisor mode with traps disabled, but with all traps delegated to
+///   supervisor mode.
+/// - Any other harts must not be running concurrently with us. TODO: Define their state.
+#[no_mangle]
+pub unsafe extern "C" fn hart0_boot(stack_canary: u64) -> ! {
+    assert_eq!(stack_canary, 0xdead0bad0defaced);
+
+    /*
     // After this point, everything else is for debugging.
     #[cfg(target_arch = "riscv64")]
     {
@@ -98,6 +125,11 @@ pub unsafe extern "C" fn hart0_boot(device_tree: *const u8) -> ! {
             .unwrap_or_else(|err| void::unreachable(err));
         arch::interrupts::example_timer();
     }
+    */
+
+    if true {
+        todo!();
+    }
     info!("sleeping forever...");
     sleep_forever();
 }