From 9e223ca5d020102ee55121b018fa7ca1dd99e964 Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Sun, 8 Feb 2026 12:47:28 +0000
Subject: [PATCH] x86_64: implement syscall instruction init and dispatch

---
 arch/x86_64/irq.c | 79 +++++++++++++++++++++++++++++++----------------
 1 file changed, 52 insertions(+), 27 deletions(-)

diff --git a/arch/x86_64/irq.c b/arch/x86_64/irq.c
index f16c748..320bd8e 100644
--- a/arch/x86_64/irq.c
+++ b/arch/x86_64/irq.c
@@ -1,4 +1,5 @@
 #include <arch/irq.h>
+#include <arch/msr.h>
 #include <arch/ports.h>
 #include <mango/cpu.h>
 #include <mango/libc/string.h>
@@ -20,6 +21,27 @@ static struct idt idt;
 static int idt_initialised = 0;
 static uintptr_t int_entry_points[NR_IDT_ENTRIES];
 
+static void set_syscall_gate(uintptr_t rip)
+{
+	uint64_t user_cs = 0x13;
+	uint64_t kernel_cs = 0x8;
+
+	uintptr_t star_reg = 0xC0000081;
+	uintptr_t lstar_reg = 0xC0000082;
+	uintptr_t sfmask_reg = 0xC0000084;
+
+	uint64_t selectors = 0;
+	selectors |= (user_cs) << 48;
+	selectors |= (kernel_cs) << 32;
+
+	/* disable interrupts */
+	uint64_t flag_mask = 0x200;
+
+	wrmsr(star_reg, selectors);
+	wrmsr(lstar_reg, rip);
+	wrmsr(sfmask_reg, flag_mask);
+}
+
 static void set_idt_gate(
 	struct idt *idt,
 	uint8_t index,
@@ -65,33 +87,6 @@ static void pf_handler(struct ml_cpu_context *regs)
 		regs->err_no);
 }
 
-#if 0
-static void set_syscall_gate(uintptr_t rip)
-{
-	/* sysret adds 0x10 to this to get cs, and 0x8 to get ss
-	 * note that the CPU should force the RPL to 3 when loading
-	 * the selector by using user_cs | 3. However, this doesn't happen
-	 * in certain scenarios (specifically, QEMU + KVM on a Ryzen 5 1600X). */
-	uint64_t user_cs = 0x13;
-	uint64_t kernel_cs = 0x8;
-
-	uintptr_t star_reg = 0xC0000081;
-	uintptr_t lstar_reg = 0xC0000082;
-	uintptr_t sfmask_reg = 0xC0000084;
-
-	uint64_t selectors = 0;
-	selectors |= (user_cs) << 48;
-	selectors |= (kernel_cs) << 32;
-
-	/* disable interrupts */
-	uint64_t flag_mask = 0x200;
-
-	write_msr(star_reg, selectors);
-	write_msr(lstar_reg, rip);
-	write_msr(sfmask_reg, flag_mask);
-}
-#endif
-
 static void init_pic(void)
 {
 	// Remap the PIC
@@ -180,6 +175,36 @@ void irq_dispatch(struct ml_cpu_context *regs)
 
 void syscall_dispatch(struct ml_cpu_context *regs)
 {
+	unsigned int sysid = regs->rax;
+	virt_addr_t syscall_impl = 0;   // TODO
+
+	if (syscall_impl == 0) {
+		regs->rax = KERN_UNSUPPORTED;
+		return;
+	}
+
+#define SYSCALL_SIGNATURE(...)                                                 \
+	intptr_t (*__VA_ARGS__)(                                               \
+		uintptr_t,                                                     \
+		uintptr_t,                                                     \
+		uintptr_t,                                                     \
+		uintptr_t,                                                     \
+		uintptr_t,                                                     \
+		uintptr_t,                                                     \
+		uintptr_t,                                                     \
+		uintptr_t)
+
+	SYSCALL_SIGNATURE(fn) = (SYSCALL_SIGNATURE())syscall_impl;
+
+	regs->rax
+		= fn(regs->rdi,
+	             regs->rsi,
+	             regs->rdx,
+	             regs->r12,
+	             regs->r8,
+	             regs->r9,
+	             regs->r13,
+	             regs->r14);
 }
 
 void hook_irq(enum irq_vector vec, struct irq_hook *hook)