ptos/amd64+ke: Add system call groundwork + exit syscall

Signed-off-by: Chloe M. <chloe@mensia.org>

service/ptos/arch/amd64/cpu/init.c

@@ -38,6 +38,7 @@ InitInterrupts(VOID)
     MdIdtSetGate(0x0C, (UPTR)TrapStackSegmentFault, IDT_TRAP_GATE, 0);
     MdIdtSetGate(0x0D, (UPTR)TrapGeneralProtection, IDT_TRAP_GATE, 0);
     MdIdtSetGate(0x0E, (UPTR)TrapPageFault, IDT_TRAP_GATE, 0);
+    MdIdtSetGate(0x2E, (UPTR)TrapLegacySyscall, IDT_USER_GATE, 0);
     MdIdtLoad();
 }
 

service/ptos/arch/amd64/cpu/vector.S

@@ -151,3 +151,10 @@ LapicTmrIsr:
     call HalContextSwitch
     call MdLapicSendEoi
     INTR_EXIT()
+
+    .globl TrapLegacySyscall
+TrapLegacySyscall:
+    INTR_ENTRY($0x2C)
+    mov %rsp, %rdi
+    call MdSyscallDispatch
+    INTR_EXIT()

service/ptos/arch/amd64/ke/syscall.c

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: System call dispatch
+ * Author:      Chloe M.
+ */
+
+#include <ke/syscall.h>
+#include <machine/frame.h>
+
+/*
+ * Dispatch incoming system calls
+ *
+ * @Frame:  Trapframe snapshot
+ */
+VOID
+MdSyscallDispatch(TRAP_FRAME *Frame)
+{
+    SYSCALL_ARGS ScArgs;
+
+    if (Frame == NULL) {
+        return;
+    }
+
+    /* Is this system call number valid? */
+    if (Frame->Rax == 0 || Frame->Rax >= _SYSCALL_MAX) {
+        Frame->Rax = STATUS_INVALID_PARAM;
+        return;
+    }
+
+    ScArgs.Arg[0] = Frame->Rdi;
+    ScArgs.Arg[1] = Frame->Rsi;
+    ScArgs.Arg[2] = Frame->Rdx;
+    ScArgs.Arg[3] = Frame->Rcx;
+    ScArgs.Arg[4] = Frame->R8;
+    ScArgs.Arg[5] = Frame->R9;
+    SystemCallTable[Frame->Rax](&ScArgs);
+}