fix(x86_64): don't use boot info in SMP start

Author: mkroening

src/arch/x86_64/kernel/apic.rs

@@ -728,7 +728,7 @@ pub fn init_x2apic() {
 	}
 }
 
-/// Initialize the required _start variables for the next CPU to be booted.
+/// Initialize the required `smp::start` variables for the next CPU to be booted.
 #[cfg(feature = "smp")]
 pub fn init_next_processor_variables() {
 	use alloc::alloc::alloc;
@@ -751,7 +751,6 @@ pub fn init_next_processor_variables() {
 /// This is partly confirmed by <https://wiki.osdev.org/Symmetric_Multiprocessing>
 #[cfg(all(target_os = "none", feature = "smp"))]
 pub fn boot_application_processors() {
-	use hermit_entry::boot_info::RawBootInfo;
 	use x86_64::structures::paging::Translate;
 
 	let smp_boot_code = include_bytes!(concat!(core::env!("OUT_DIR"), "/boot.bin"));
@@ -797,11 +796,11 @@ pub fn boot_application_processors() {
 		// Set entry point
 		debug!(
 			"Set entry point for application processor to {:p}",
-			arch::start::hermit_entry::_start as *const ()
+			arch::start::smp::start as *const ()
 		);
 		(SMP_BOOT_CODE_ADDRESS + SMP_BOOT_CODE_OFFSET_ENTRY)
-			.as_mut_ptr::<unsafe extern "C" fn(Option<&'static RawBootInfo>, cpu_id: u32) -> !>()
-			.write_unaligned(arch::start::hermit_entry::_start);
+			.as_mut_ptr::<unsafe extern "C" fn() -> !>()
+			.write_unaligned(arch::start::smp::start);
 	}
 
 	// Now wake up each application processor.

src/arch/x86_64/start/mod.rs

@@ -1 +1,3 @@
 pub mod hermit_entry;
+#[cfg(feature = "smp")]
+pub mod smp;

src/arch/x86_64/start/smp.rs

@@ -0,0 +1,33 @@
+use x86_64::registers::control::{Cr0, Cr0Flags};
+
+use crate::arch::kernel::scheduler::TaskStacks;
+use crate::config::KERNEL_STACK_SIZE;
+use crate::kernel::CURRENT_STACK_ADDRESS;
+
+#[unsafe(naked)]
+pub unsafe extern "C" fn start() -> ! {
+	core::arch::naked_asm!(
+		// Overwrite RSP with `CURRENT_STACK_ADDRESS`
+		"mov rax, qword ptr [rip + {current_stack_address}@GOTPCREL]",
+		"mov rsp, qword ptr [rax]",
+
+		// Add top stack offset
+		"add rsp, {stack_top_offset}",
+
+		// Jump into Rust code
+		"jmp {start_rust}",
+
+		current_stack_address = sym CURRENT_STACK_ADDRESS,
+		stack_top_offset = const KERNEL_STACK_SIZE - TaskStacks::MARKER_SIZE,
+		start_rust = sym start_rust,
+	)
+}
+
+unsafe extern "C" fn start_rust() -> ! {
+	// Enable caching
+	unsafe {
+		Cr0::update(|flags| flags.remove(Cr0Flags::CACHE_DISABLE | Cr0Flags::NOT_WRITE_THROUGH));
+	}
+
+	crate::application_processor_main();
+}