fix(x86_64): make CoreLocal #[repr(Rust)] again

src/arch/x86_64/kernel/core_local.rs

@@ -2,8 +2,8 @@ use alloc::boxed::Box;
 use alloc::vec::Vec;
 use core::arch::asm;
 use core::cell::{Cell, RefCell, RefMut};
-use core::ptr;
 use core::sync::atomic::Ordering;
+use core::{mem, ptr};
 
 #[cfg(feature = "smp")]
 use hermit_sync::InterruptTicketMutex;
@@ -18,7 +18,6 @@ use crate::executor::task::AsyncTask;
 use crate::scheduler::SchedulerInput;
 use crate::scheduler::{CoreId, PerCoreScheduler};
 
-#[repr(C)]
 pub(crate) struct CoreLocal {
 	this: *const Self,
 	/// Sequential ID of this CPU Core.
@@ -81,7 +80,7 @@ impl CoreLocal {
 		debug_assert_ne!(VirtAddr::zero(), GsBase::read());
 		unsafe {
 			let raw: *const Self;
-			asm!("mov {}, gs:0", out(reg) raw, options(nomem, nostack, preserves_flags));
+			asm!("mov {}, gs:{}", out(reg) raw, const mem::offset_of!(Self, this), options(nomem, nostack, preserves_flags));
 			&*raw
 		}
 	}

src/arch/x86_64/kernel/mod.rs

@@ -314,7 +314,7 @@ where
 	if tls_size > 0 {
 		// To access TLS blocks on x86-64, TLS offsets are *subtracted* from the thread register value.
 		// So the thread pointer needs to be `block_ptr + tls_offset`.
-		// GNU style TLS requires `gs:0` to represent the same address as the thread pointer.
+		// GNU style TLS requires `fs:0` to represent the same address as the thread pointer.
 		// Since the thread pointer points to the end of the TLS blocks, we need to store it there.
 		let tcb_size = core::mem::size_of::<*mut ()>();
 		let tls_offset = tls_size as usize;

src/arch/x86_64/kernel/scheduler.rs

@@ -273,7 +273,7 @@ impl TaskTLS {
 		let mut block = {
 			// To access TLS blocks on x86-64, TLS offsets are *subtracted* from the thread register value.
 			// So the thread pointer needs to be `block_ptr + tls_offset`.
-			// GNU style TLS requires `gs:0` to represent the same address as the thread pointer.
+			// GNU style TLS requires `fs:0` to represent the same address as the thread pointer.
 			// Since the thread pointer points to the end of the TLS blocks, we need to store it there.
 			let tcb_size = mem::size_of::<*mut ()>();
 

src/arch/x86_64/kernel/syscall.rs

@@ -1,5 +1,7 @@
 use core::arch::asm;
+use core::mem;
 
+use super::core_local::CoreLocal;
 use crate::syscalls::table::SYSHANDLER_TABLE;
 
 #[no_mangle]
@@ -19,7 +21,7 @@ pub(crate) unsafe extern "C" fn syscall_handler() -> ! {
 			// switch to kernel stack
 			"swapgs",
 			"mov rcx, rsp",
-			"mov rsp, gs:32",
+			"mov rsp, gs:{core_local_kernel_stack}",
 			// save user stack pointer
 			"push rcx",
 			// copy 4th argument to rcx to adhere x86_64 ABI
@@ -42,6 +44,7 @@ pub(crate) unsafe extern "C" fn syscall_handler() -> ! {
 			"pop rdx",
 			"pop rcx",
 			"sysretq",
+			core_local_kernel_stack = const mem::offset_of!(CoreLocal, kernel_stack),
 			table = sym SYSHANDLER_TABLE,
 			options(noreturn)
 		);