feat: initial scalable x86_64 microkernel skeleton with Limine, Rust, C HAL, and C++20 IPC

kernel/asm/context.S

@@ -0,0 +1,33 @@
+/* opencoreC - Thread Context Switch */
+.global switch_to
+
+.section .text
+/*
+ * void switch_to(uint64_t **prev_rsp_ptr, uint64_t *next_rsp);
+ * RDI = pointer to current thread's stored RSP
+ * RSI = target thread's RSP
+ */
+switch_to:
+    /* Push callee-saved registers of outgoing thread */
+    push rbp
+    push rbx
+    push r12
+    push r13
+    push r14
+    push r15
+
+    /* Save current stack pointer */
+    mov [rdi], rsp
+
+    /* Load target stack pointer */
+    mov rsp, rsi
+
+    /* Pop callee-saved registers of incoming thread */
+    pop r15
+    pop r14
+    pop r13
+    pop r12
+    pop rbx
+    pop rbp
+
+    ret

kernel/asm/syscall_entry.S

@@ -0,0 +1,53 @@
+/* opencoreC - Fast Syscall Entry Trampoline (x86_64) */
+.global syscall_entry
+.extern kernel_syscall_dispatcher
+
+.section .bss
+.align 16
+user_scratch_rsp:
+    .quad 0
+kernel_temp_stack:
+    .skip 4096
+kernel_temp_stack_top:
+
+.section .text
+syscall_entry:
+    /* Save user stack pointer */
+    mov [rip + user_scratch_rsp], rsp
+    lea rsp, [rip + kernel_temp_stack_top]
+
+    /* Save user RIP (in RCX) and user RFLAGS (in R11) */
+    push rcx
+    push r11
+
+    /* Save argument and volatile registers to construct SyscallRegisters */
+    push rax
+    push rdi
+    push rsi
+    push rdx
+    push r8
+    push r9
+    push r10
+
+    /* Pass pointer to SyscallRegisters struct in RDI */
+    mov rdi, rsp
+    call kernel_syscall_dispatcher
+
+    /* Restore registers (rax, rdx, r8 may have return values from dispatcher) */
+    pop r10
+    pop r9
+    pop r8
+    pop rdx
+    pop rsi
+    pop rdi
+    pop rax
+
+    /* Restore user RIP and RFLAGS */
+    pop r11
+    pop rcx
+
+    /* Restore user stack */
+    mov rsp, [rip + user_scratch_rsp]
+
+    /* Return to Ring 3 */
+    sysretq