From e52268cd8e45c4b57ecbb4b111917125bb231a00 Mon Sep 17 00:00:00 2001
From: kamkow1 <kamkow256@gmail.com>
Date: Sat, 3 Jan 2026 02:04:09 +0100
Subject: [PATCH] First Hello world syscall

---
 .gdbinit                    |  2 ++
 amd64/link.ld               |  2 +-
 aux/qemu_amd64_debug.sh     |  5 ++++
 init/init.S                 |  3 +++
 kernel/amd64/bootmain.c     |  8 +++---
 kernel/amd64/debug.c        |  7 +++++
 kernel/amd64/flags.mk       |  3 ++-
 kernel/amd64/gdt.h          |  6 +++++
 kernel/amd64/init.c         |  9 +++----
 kernel/amd64/intr.c         |  9 ++++---
 kernel/amd64/intr_stub.S    | 52 +++----------------------------------
 kernel/amd64/proc.c         | 20 ++++++++------
 kernel/amd64/proc.h         |  4 +--
 kernel/amd64/regsasm.h      | 38 +++++++++++++++++++++++++++
 kernel/amd64/sched.S        | 24 ++---------------
 kernel/amd64/sched1.c       | 12 ++++++++-
 kernel/amd64/smp.c          | 23 ++++++++--------
 kernel/amd64/smp.h          | 26 +++++++++----------
 kernel/amd64/src.mk         | 10 ++++---
 kernel/amd64/syscall.c      | 19 ++++++++++++++
 kernel/amd64/syscallentry.S | 40 ++++++++++++++++++++++++++++
 kernel/irq/irq.h            |  3 ++-
 kernel/proc/proc.c          | 24 ++++++++---------
 kernel/sys/debug.h          |  8 +++++-
 kernel/sys/sched.h          |  5 ++--
 kernel/sys/syscall.h        |  6 +++++
 26 files changed, 228 insertions(+), 140 deletions(-)
 create mode 100644 .gdbinit
 create mode 100755 aux/qemu_amd64_debug.sh
 create mode 100644 kernel/amd64/regsasm.h
 create mode 100644 kernel/amd64/syscall.c
 create mode 100644 kernel/amd64/syscallentry.S
 create mode 100644 kernel/sys/syscall.h

diff --git a/.gdbinit b/.gdbinit
new file mode 100644
index 0000000..627235c
--- /dev/null
+++ b/.gdbinit
@@ -0,0 +1,2 @@
+file kernel/build/kernel.elf
+target remote :1234
diff --git a/amd64/link.ld b/amd64/link.ld
index 6f8fb8d..c426fc5 100644
--- a/amd64/link.ld
+++ b/amd64/link.ld
@@ -9,7 +9,7 @@ PHDRS {
 }
 
 SECTIONS {
-  . = 0x0000000050000000;
+  . = 0x0000500000000000;
 
   .text : {
     *(.text .text.*)
diff --git a/aux/qemu_amd64_debug.sh b/aux/qemu_amd64_debug.sh
new file mode 100755
index 0000000..5398848
--- /dev/null
+++ b/aux/qemu_amd64_debug.sh
@@ -0,0 +1,5 @@
+#!/bin/sh
+
+set -x
+
+qemu-system-x86_64 -M q35 -m 4G -serial stdio -cdrom mop3.iso -smp 4 -s -S $@
diff --git a/init/init.S b/init/init.S
index b7ce6f6..05375d1 100644
--- a/init/init.S
+++ b/init/init.S
@@ -2,4 +2,7 @@
 _start:
   pushq $123
   addq $8, %rsp
+
+  syscall
+
   jmp _start
diff --git a/kernel/amd64/bootmain.c b/kernel/amd64/bootmain.c
index 1fe0217..bc2bb16 100644
--- a/kernel/amd64/bootmain.c
+++ b/kernel/amd64/bootmain.c
@@ -5,6 +5,8 @@
 #include <amd64/hpet.h>
 #include <amd64/init.h>
 #include <amd64/intr_defs.h>
+#include <amd64/msr-index.h>
+#include <amd64/msr.h>
 #include <aux/compiler.h>
 #include <irq/irq.h>
 #include <libk/std.h>
@@ -16,6 +18,7 @@
 #include <sys/debug.h>
 #include <sys/mm.h>
 #include <sys/smp.h>
+#include <sys/syscall.h>
 #include <sys/time.h>
 #include <uacpi/uacpi.h>
 
@@ -32,9 +35,10 @@ ALIGNED (16) static uint8_t uacpi_memory_buffer[UACPI_MEMORY_BUFFER_MAX];
  */
 void bootmain (void) {
   struct cpu* bsp_cpu = cpu_make ();
-  cpu_assign (bsp_cpu->id);
+  amd64_thiscpu_set_init ();
 
   amd64_init (bsp_cpu, false);
+  syscall_init ();
   amd64_debug_init ();
   pmm_init ();
   mm_init ();
@@ -54,8 +58,6 @@ void bootmain (void) {
 
   mm_init2 ();
 
-  __asm__ volatile ("sti");
-
   proc_init ();
 
   for (;;)
diff --git a/kernel/amd64/debug.c b/kernel/amd64/debug.c
index 1a073f6..cdfc3d6 100644
--- a/kernel/amd64/debug.c
+++ b/kernel/amd64/debug.c
@@ -13,6 +13,8 @@
 /// Lock, which ensures that prints to the serial port are atomic
 static spin_lock_t serial_lock = SPIN_LOCK_INIT;
 
+static bool debug_init = false;
+
 /// Block until TX buffer is empty
 static bool amd64_debug_serial_tx_empty (void) {
   return (bool)(amd64_io_inb (PORT_COM1 + 5) & 0x20);
@@ -30,6 +32,9 @@ static void amd64_debug_serial_write (char x) {
  * all prints are atomic.
  */
 void debugprintf (const char* fmt, ...) {
+  if (!debug_init)
+    return;
+
   char buffer[BUFFER_SIZE];
   memset (buffer, 0, sizeof (buffer));
 
@@ -61,4 +66,6 @@ void amd64_debug_init (void) {
   amd64_io_outb (PORT_COM1 + 3, 0x03);
   amd64_io_outb (PORT_COM1 + 2, 0xC7);
   amd64_io_outb (PORT_COM1 + 4, 0x0B);
+
+  debug_init = true;
 }
diff --git a/kernel/amd64/flags.mk b/kernel/amd64/flags.mk
index 07c4f10..407b543 100644
--- a/kernel/amd64/flags.mk
+++ b/kernel/amd64/flags.mk
@@ -4,7 +4,8 @@ cflags += --target=x86_64-pc-none-elf \
 					-mno-avx \
 					-mno-mmx \
 					-mno-80387 \
-					-mno-red-zone
+					-mno-red-zone \
+					-fno-omit-frame-pointer
 
 ldflags += --target=x86_64-pc-none-elf \
 					 -Wl,-zmax-page-size=0x1000
diff --git a/kernel/amd64/gdt.h b/kernel/amd64/gdt.h
index cb6180e..3a5aba8 100644
--- a/kernel/amd64/gdt.h
+++ b/kernel/amd64/gdt.h
@@ -5,6 +5,12 @@
 #include <libk/std.h>
 #include <proc/proc.h>
 
+#define GDT_KCODE 0x08
+#define GDT_KDATA 0x10
+#define GDT_UCODE 0x18
+#define GDT_UDATA 0x20
+#define GDT_TSS   0x28
+
 /// Size of kernel stack
 #define KSTACK_SIZE (32 * 1024)
 
diff --git a/kernel/amd64/init.c b/kernel/amd64/init.c
index 422ac51..539f4f7 100644
--- a/kernel/amd64/init.c
+++ b/kernel/amd64/init.c
@@ -1,3 +1,4 @@
+#include <amd64/gdt.h>
 #include <amd64/init.h>
 #include <amd64/intr.h>
 #include <amd64/smp.h>
@@ -5,12 +6,6 @@
 #include <libk/std.h>
 #include <libk/string.h>
 
-#define GDT_KCODE 0x08
-#define GDT_KDATA 0x10
-#define GDT_UCODE 0x18
-#define GDT_UDATA 0x20
-#define GDT_TSS   0x28
-
 #define TSS         0x80
 #define TSS_PRESENT 0x89
 
@@ -70,6 +65,8 @@ static void amd64_gdt_init (struct cpu* cpu) {
                     "movw %%ax, %%ds\n"
                     "movw %%ax, %%es\n"
                     "movw %%ax, %%ss\n"
+                    "movw %%ax, %%fs\n"
+                    "movw %%ax, %%gs\n"
                     :
                     : [kcode] "i"(GDT_KCODE), [kdata] "i"(GDT_KDATA)
                     : "rax", "memory");
diff --git a/kernel/amd64/intr.c b/kernel/amd64/intr.c
index 3e3fc5d..00775eb 100644
--- a/kernel/amd64/intr.c
+++ b/kernel/amd64/intr.c
@@ -1,4 +1,5 @@
 #include <amd64/apic.h>
+#include <amd64/gdt.h>
 #include <amd64/intr.h>
 #include <amd64/intr_defs.h>
 #include <amd64/io.h>
@@ -90,7 +91,7 @@ static void amd64_init_pic (void) {
 static void amd64_idt_set (volatile struct idt_entry* ent, uint64_t handler, uint8_t flags,
                            uint8_t ist) {
   ent->intrlow = (handler & 0xFFFF);
-  ent->kernel_cs = 0x08; // GDT_KCODE (init.c)
+  ent->kernel_cs = GDT_KCODE;
   ent->ist = ist;
   ent->attrs = flags;
   ent->intrmid = ((handler >> 16) & 0xFFFF);
@@ -163,7 +164,7 @@ static void amd64_intr_exception (struct saved_regs* regs) {
                regs->error, regs->rip, regs->cs, regs->rflags, regs->rsp, regs->ss, cr2, cr3,
                regs->rbx);
 
-  if (regs->cs == (0x18 | 0x03)) {
+  if (regs->cs == (GDT_UCODE | 0x03)) {
     proc_kill (thiscpu->proc_current);
   } else {
     spin ();
@@ -182,12 +183,12 @@ void amd64_intr_handler (void* stack_ptr) {
     struct irq* irq = irq_find (regs->trap);
 
     if (irq != NULL) {
-      if (!(irq->flags & IRQ_INTERRUPT_SAFE))
+      if ((irq->flags & IRQ_INTERRUPT_SAFE))
         __asm__ volatile ("sti");
 
       irq->func (irq->arg, stack_ptr);
 
-      if (!(irq->flags & IRQ_INTERRUPT_SAFE))
+      if ((irq->flags & IRQ_INTERRUPT_SAFE))
         __asm__ volatile ("cli");
     }
   }
diff --git a/kernel/amd64/intr_stub.S b/kernel/amd64/intr_stub.S
index 1085dc7..3f34e02 100644
--- a/kernel/amd64/intr_stub.S
+++ b/kernel/amd64/intr_stub.S
@@ -1,4 +1,5 @@
 #include <amd64/intr_defs.h>
+#include <amd64/regsasm.h>
 
 .extern amd64_intr_handler
 
@@ -9,67 +10,20 @@
   pushq $0; \
   pushq $z;
 
-#define push_regs \
-  pushq %rax; \
-  pushq %rcx; \
-  pushq %rdx; \
-  pushq %rsi; \
-  pushq %rdi; \
-  pushq %rbp; \
-  pushq %rbx; \
-  pushq %r8; \
-  pushq %r9; \
-  pushq %r10; \
-  pushq %r11; \
-  pushq %r12; \
-  pushq %r13; \
-  pushq %r14; \
-  pushq %r15;
-
-#define pop_regs \
-  popq %r15; \
-  popq %r14; \
-  popq %r13; \
-  popq %r12; \
-  popq %r11; \
-  popq %r10; \
-  popq %r9; \
-  popq %r8; \
-  popq %rbx; \
-  popq %rbp; \
-  popq %rdi; \
-  popq %rsi; \
-  popq %rdx; \
-  popq %rcx; \
-  popq %rax;
-
 #define make_intr_stub(x, n) \
   .global amd64_intr ## n; \
   amd64_intr ## n:; \
   x(n); \
   cli; \
-  movq %rsp, %rax; \
-  movq 144(%rax), %rax; \
-  testb $3, %al; \
-  jz 1f; \
-  swapgs; \
-1:; \
   push_regs; \
   cld; \
   movq %rsp, %rdi; \
-  movq %rsp, %rax; \
+  movq %rsp, %rbp; \
   subq $8, %rsp; \
   andq $~0xF, %rsp; \
-  movq %rax, (%rsp); \
   callq amd64_intr_handler; \
-  movq (%rsp), %rsp; \
+  movq %rbp, %rsp; \
   pop_regs; \
-  movq %rsp, %rax; \
-  movq 144(%rax), %rax; \
-  testb $3, %al; \
-  jz 2f; \
-  swapgs; \
-2:; \
   addq $16, %rsp; \
   iretq;
   
diff --git a/kernel/amd64/proc.c b/kernel/amd64/proc.c
index 6fcd58f..f7cd89d 100644
--- a/kernel/amd64/proc.c
+++ b/kernel/amd64/proc.c
@@ -1,12 +1,17 @@
+#include <amd64/gdt.h>
 #include <aux/elf.h>
 #include <libk/std.h>
 #include <libk/string.h>
+#include <limine/requests.h>
 #include <mm/liballoc.h>
 #include <mm/pmm.h>
 #include <proc/proc.h>
 #include <sync/spin_lock.h>
+#include <sys/debug.h>
 
 struct proc* proc_from_elf (uint8_t* elf_contents) {
+  struct limine_hhdm_response* hhdm = limine_hhdm_request.response;
+
   struct proc* proc = malloc (sizeof (*proc));
   if (proc == NULL)
     return NULL;
@@ -20,22 +25,21 @@ struct proc* proc_from_elf (uint8_t* elf_contents) {
     return NULL;
   }
 
-  proc->pdata.syscall_stack = pmm_alloc (KSTACK_SIZE / PAGE_SIZE);
-  if (proc->pdata.syscall_stack == PMM_ALLOC_ERR) {
+  proc->pdata.kernel_stack = pmm_alloc (KSTACK_SIZE / PAGE_SIZE);
+  if (proc->pdata.kernel_stack == PMM_ALLOC_ERR) {
     free (proc);
     return NULL;
   }
+  uintptr_t kernel_stack = proc->pdata.kernel_stack;
+  proc->pdata.kernel_stack += (uintptr_t)hhdm->offset + KSTACK_SIZE;
 
   proc->pdata.user_stack = pmm_alloc (USTACK_SIZE / PAGE_SIZE);
   if (proc->pdata.user_stack == PMM_ALLOC_ERR) {
     free (proc);
-    pmm_free (proc->pdata.syscall_stack, USTACK_SIZE / PAGE_SIZE);
+    pmm_free (kernel_stack, USTACK_SIZE / PAGE_SIZE);
     return NULL;
   }
-
   uintptr_t user_stack = proc->pdata.user_stack;
-
-  proc->pdata.syscall_stack += KSTACK_SIZE;
   proc->pdata.user_stack += USTACK_SIZE;
 
   proc_map (proc, user_stack, PROC_USTACK_TOP - USTACK_SIZE, USTACK_SIZE / PAGE_SIZE,
@@ -43,10 +47,10 @@ struct proc* proc_from_elf (uint8_t* elf_contents) {
 
   struct elf_aux aux = proc_load_segments (proc, elf_contents);
 
-  proc->pdata.regs.ss = 0x20 | 0x03;
+  proc->pdata.regs.ss = GDT_UDATA | 0x03;
   proc->pdata.regs.rsp = (uint64_t)PROC_USTACK_TOP;
   proc->pdata.regs.rflags = 0x202;
-  proc->pdata.regs.cs = 0x18 | 0x03;
+  proc->pdata.regs.cs = GDT_UCODE | 0x03;
   proc->pdata.regs.rip = aux.entry;
   proc->lock = SPIN_LOCK_INIT;
   atomic_store (&proc->state, PROC_READY);
diff --git a/kernel/amd64/proc.h b/kernel/amd64/proc.h
index c900f7a..fb85fbc 100644
--- a/kernel/amd64/proc.h
+++ b/kernel/amd64/proc.h
@@ -12,9 +12,9 @@
 /// Platform-dependent process data
 struct proc_platformdata {
   struct saved_regs regs;
-  uintptr_t syscall_stack;
   uintptr_t user_stack;
-  uint64_t fsbase;
+  uintptr_t kernel_stack;
+  uint64_t gs_base;
 };
 
 #endif // _KERNEL_AMD64_PROC_H
diff --git a/kernel/amd64/regsasm.h b/kernel/amd64/regsasm.h
new file mode 100644
index 0000000..a8998fd
--- /dev/null
+++ b/kernel/amd64/regsasm.h
@@ -0,0 +1,38 @@
+#ifndef _KERNEL_AMD64_REGSASM_H
+#define _KERNEL_AMD64_REGSASM_H
+
+#define push_regs                                                                                  \
+  pushq % rax;                                                                                     \
+  pushq % rcx;                                                                                     \
+  pushq % rdx;                                                                                     \
+  pushq % rsi;                                                                                     \
+  pushq % rdi;                                                                                     \
+  pushq % rbp;                                                                                     \
+  pushq % rbx;                                                                                     \
+  pushq % r8;                                                                                      \
+  pushq % r9;                                                                                      \
+  pushq % r10;                                                                                     \
+  pushq % r11;                                                                                     \
+  pushq % r12;                                                                                     \
+  pushq % r13;                                                                                     \
+  pushq % r14;                                                                                     \
+  pushq % r15;
+
+#define pop_regs                                                                                   \
+  popq % r15;                                                                                      \
+  popq % r14;                                                                                      \
+  popq % r13;                                                                                      \
+  popq % r12;                                                                                      \
+  popq % r11;                                                                                      \
+  popq % r10;                                                                                      \
+  popq % r9;                                                                                       \
+  popq % r8;                                                                                       \
+  popq % rbx;                                                                                      \
+  popq % rbp;                                                                                      \
+  popq % rdi;                                                                                      \
+  popq % rsi;                                                                                      \
+  popq % rdx;                                                                                      \
+  popq % rcx;                                                                                      \
+  popq % rax;
+
+#endif // _KERNEL_AMD64_REGSASM_H
diff --git a/kernel/amd64/sched.S b/kernel/amd64/sched.S
index e21941c..c44f1cc 100644
--- a/kernel/amd64/sched.S
+++ b/kernel/amd64/sched.S
@@ -1,30 +1,10 @@
-#define pop_regs \
-  popq %r15; \
-  popq %r14; \
-  popq %r13; \
-  popq %r12; \
-  popq %r11; \
-  popq %r10; \
-  popq %r9; \
-  popq %r8; \
-  popq %rbx; \
-  popq %rbp; \
-  popq %rdi; \
-  popq %rsi; \
-  popq %rdx; \
-  popq %rcx; \
-  popq %rax;
+#include <amd64/regsasm.h>
 
 .global amd64_do_sched
 amd64_do_sched:
+  cli
   movq %rsi, %cr3
   movq %rdi, %rsp
   pop_regs
-
-  movq 144(%rsp), %rax
-  testb $3, %al
-  jz 1f
-  swapgs
-1:
   add $16, %rsp
   iretq
diff --git a/kernel/amd64/sched1.c b/kernel/amd64/sched1.c
index 270d253..248b3ba 100644
--- a/kernel/amd64/sched1.c
+++ b/kernel/amd64/sched1.c
@@ -1,4 +1,14 @@
+#include <amd64/msr-index.h>
+#include <amd64/msr.h>
 #include <amd64/sched.h>
+#include <libk/std.h>
+#include <proc/proc.h>
 #include <sys/mm.h>
+#include <sys/smp.h>
 
-void do_sched (void* regs, struct pd* pd) { amd64_do_sched (regs, (void*)pd->cr3_paddr); }
+void do_sched (struct proc* proc) {
+  thiscpu->tss.rsp0 = proc->pdata.kernel_stack;
+  thiscpu->syscall_kernel_stack = proc->pdata.kernel_stack;
+  amd64_wrmsr (MSR_GS_BASE, proc->pdata.gs_base);
+  amd64_do_sched ((void*)&proc->pdata.regs, (void*)proc->pd.cr3_paddr);
+}
diff --git a/kernel/amd64/smp.c b/kernel/amd64/smp.c
index 6b07909..acdbe80 100644
--- a/kernel/amd64/smp.c
+++ b/kernel/amd64/smp.c
@@ -10,6 +10,7 @@
 #include <sync/spin_lock.h>
 #include <sys/debug.h>
 #include <sys/smp.h>
+#include <sys/syscall.h>
 
 /// Cpu ID counter
 static uint32_t cpu_counter = 0;
@@ -18,6 +19,10 @@ static spin_lock_t cpu_counter_lock = SPIN_LOCK_INIT;
 /// The CPUs
 static struct cpu cpus[CPUS_MAX];
 
+static bool thiscpu_init = false;
+
+void amd64_thiscpu_set_init (void) { thiscpu_init = true; }
+
 /// Allocate a CPU structure
 struct cpu* cpu_make (void) {
   spin_lock (&cpu_counter_lock);
@@ -30,30 +35,26 @@ struct cpu* cpu_make (void) {
   cpu->lock = SPIN_LOCK_INIT;
   cpu->id = id;
 
-  return cpu_get (id);
+  amd64_wrmsr (MSR_SHADOW_GS_BASE, (uint64_t)cpu);
+
+  return cpu;
 }
 
-struct cpu* cpu_get (uint32_t id) {
-  if (id >= CPUS_MAX)
+struct cpu* cpu_get (void) {
+  if (!thiscpu_init)
     return NULL;
 
-  return &cpus[id];
+  return (struct cpu*)amd64_rdmsr (MSR_SHADOW_GS_BASE);
 }
 
-/// Get ID of current running CPU
-uint32_t cpu_id (void) { return (uint32_t)amd64_rdmsr (MSR_SHADOW_GS_BASE); }
-
-/// Assign an ID to the current running CPU
-void cpu_assign (uint32_t id) { amd64_wrmsr (MSR_SHADOW_GS_BASE, (uint64_t)id); }
-
 /// Bootstrap code for non-BSP CPUs
 static void amd64_smp_bootstrap (struct limine_mp_info* mp_info) {
   amd64_load_kernel_cr3 ();
 
   struct cpu* cpu = cpu_make ();
-  cpu_assign (cpu->id);
 
   amd64_init (cpu, true); /* gdt + idt */
+  syscall_init ();
 
   thiscpu->lapic_ticks = amd64_lapic_init (2500);
   amd64_lapic_tick (thiscpu->lapic_ticks);
diff --git a/kernel/amd64/smp.h b/kernel/amd64/smp.h
index df4b0db..33a3318 100644
--- a/kernel/amd64/smp.h
+++ b/kernel/amd64/smp.h
@@ -10,6 +10,15 @@
 #define CPUS_MAX 32
 
 struct cpu {
+  /* for syscall instruction */
+  uintptr_t syscall_user_stack;
+  uintptr_t syscall_kernel_stack;
+  volatile uint8_t kernel_stack[KSTACK_SIZE] ALIGNED (16);
+  volatile uint8_t except_stack[KSTACK_SIZE] ALIGNED (16);
+  volatile uint8_t irq_stack[KSTACK_SIZE] ALIGNED (16);
+  volatile struct gdt_extended gdt ALIGNED (16);
+  volatile struct tss tss;
+
   uint64_t lapic_ticks;
   uint32_t id;
 
@@ -18,25 +27,16 @@ struct cpu {
     atomic_int nesting;
   } irq_ctx;
 
-  uint8_t user_stack[USTACK_SIZE] ALIGNED (16);
-
-  volatile uint8_t kernel_stack[KSTACK_SIZE] ALIGNED (16);
-  volatile uint8_t except_stack[KSTACK_SIZE] ALIGNED (16);
-  volatile uint8_t irq_stack[KSTACK_SIZE] ALIGNED (16);
-  volatile struct gdt_extended gdt ALIGNED (16);
-  volatile struct tss tss;
-
   spin_lock_t lock;
 
   struct proc* proc_run_q;
   struct proc* proc_current;
-};
+} PACKED;
 
 struct cpu* cpu_make (void);
-struct cpu* cpu_get (uint32_t id);
-void cpu_assign (uint32_t id);
-uint32_t cpu_id (void);
+struct cpu* cpu_get (void);
+void amd64_thiscpu_set_init (void);
 
-#define thiscpu (cpu_get (cpu_id ()))
+#define thiscpu (cpu_get ())
 
 #endif // _KERNEL_AMD64_SMP_H
diff --git a/kernel/amd64/src.mk b/kernel/amd64/src.mk
index 17a6e03..8ec4433 100644
--- a/kernel/amd64/src.mk
+++ b/kernel/amd64/src.mk
@@ -11,11 +11,13 @@ c += amd64/bootmain.c \
 		 amd64/time.c \
 		 amd64/smp.c \
 		 amd64/sched1.c \
-		 amd64/proc.c
+		 amd64/proc.c \
+		 amd64/syscall.c
 
 S += amd64/intr_stub.S \
 		 amd64/spin.S \
-		 amd64/sched.S
+		 amd64/sched.S \
+		 amd64/syscallentry.S
 
 o += amd64/bootmain.o \
 		 amd64/init.o \
@@ -33,4 +35,6 @@ o += amd64/bootmain.o \
 		 amd64/smp.o \
 		 amd64/sched.o \
 		 amd64/sched1.o \
-		 amd64/proc.o
+		 amd64/proc.o \
+		 amd64/syscall.o \
+		 amd64/syscallentry.o
diff --git a/kernel/amd64/syscall.c b/kernel/amd64/syscall.c
new file mode 100644
index 0000000..21d3022
--- /dev/null
+++ b/kernel/amd64/syscall.c
@@ -0,0 +1,19 @@
+#include <amd64/gdt.h>
+#include <amd64/intr.h>
+#include <amd64/msr-index.h>
+#include <amd64/msr.h>
+#include <sys/debug.h>
+
+extern void amd64_syscall_entry (void);
+
+void amd64_syscall_dispatch (void* stack_ptr) {
+  struct saved_regs* regs = stack_ptr;
+  DEBUG ("hello syscall\n");
+}
+
+void syscall_init (void) {
+  amd64_wrmsr (MSR_STAR, ((uint64_t)GDT_KCODE << 32) | ((uint64_t)(GDT_UCODE - 16) << 48));
+  amd64_wrmsr (MSR_LSTAR, (uint64_t)&amd64_syscall_entry);
+  amd64_wrmsr (MSR_SYSCALL_MASK, (1ULL << 9));
+  amd64_wrmsr (MSR_EFER, amd64_rdmsr (MSR_EFER) | EFER_SCE);
+}
diff --git a/kernel/amd64/syscallentry.S b/kernel/amd64/syscallentry.S
new file mode 100644
index 0000000..724c123
--- /dev/null
+++ b/kernel/amd64/syscallentry.S
@@ -0,0 +1,40 @@
+#include <amd64/regsasm.h>
+
+.extern amd64_syscall_dispatch
+
+dupa:
+jmp dupa
+
+.global amd64_syscall_entry
+amd64_syscall_entry:
+  cli
+  swapgs
+
+  movq %rsp, %gs:0
+  movq %gs:8, %rsp
+ 
+  pushq $0x23
+  pushq %gs:0
+  pushq %r11
+  pushq $0x1b
+  pushq %rcx
+  pushq $0
+  pushq $0
+  push_regs
+  cld
+  movq %rsp, %rdi
+  movq %rsp, %rbp
+  subq $8, %rsp
+  andq $~0xF, %rsp
+  callq amd64_syscall_dispatch
+  movq %rbp, %rsp
+  pop_regs
+  cli
+  addq $16, %rsp
+  popq %rcx
+  addq $8, %rsp
+  popq %r11
+  addq $16, %rsp
+  movq %gs:0, %rsp
+  swapgs
+  sysretq
diff --git a/kernel/irq/irq.h b/kernel/irq/irq.h
index 7771ae5..3123dad 100644
--- a/kernel/irq/irq.h
+++ b/kernel/irq/irq.h
@@ -3,7 +3,8 @@
 
 #include <libk/std.h>
 
-#define IRQ_INTERRUPT_SAFE (1 << 0)
+#define IRQ_INTERRUPT_SAFE   (1 << 0)
+#define IRQ_INTERRUPT_UNSAFE (1 << 1)
 
 typedef void (*irq_func_t) (void* arg, void* regs);
 
diff --git a/kernel/proc/proc.c b/kernel/proc/proc.c
index 96a039e..65b8b70 100644
--- a/kernel/proc/proc.c
+++ b/kernel/proc/proc.c
@@ -108,25 +108,26 @@ static struct proc* proc_spawn_rd (char* name) {
   return proc_from_elf (rd_file->content);
 }
 
-static void proc_register (struct proc* proc) {
+static void proc_register_for_cpu (struct proc* proc, struct cpu* cpu) {
   /* make available globally. */
   struct procw* procw = malloc (sizeof (*procw));
   if (procw == NULL)
     return;
   procw->proc = proc;
   proc->procw = procw;
+  proc->cpu = cpu;
 
   spin_lock (&procs_lock);
 
-  spin_lock (&thiscpu->lock);
+  spin_lock (&cpu->lock);
 
   linklist_append (struct procw*, procs, procw);
-  linklist_append (struct proc*, thiscpu->proc_run_q, proc);
+  linklist_append (struct proc*, cpu->proc_run_q, proc);
 
-  if (thiscpu->proc_current == NULL)
-    thiscpu->proc_current = proc;
+  if (cpu->proc_current == NULL)
+    cpu->proc_current = proc;
 
-  spin_unlock (&thiscpu->lock);
+  spin_unlock (&cpu->lock);
 
   spin_unlock (&procs_lock);
 }
@@ -170,9 +171,8 @@ void proc_sched (void) {
 
   spin_unlock (&thiscpu->lock);
 
-  if (next != NULL && atomic_load (&next->state) == PROC_READY) {
-    do_sched (&next->pdata.regs, &next->pd);
-  }
+  if (next != NULL && atomic_load (&next->state) == PROC_READY)
+    do_sched (next);
 
 idle:
   spin ();
@@ -190,11 +190,11 @@ static void proc_irq_sched (void* arg, void* regs) {
 
 void proc_init (void) {
   struct proc* init = proc_spawn_rd ("init.exe");
-  proc_register (init);
+  proc_register_for_cpu (init, thiscpu);
 
 #if defined(__x86_64__)
-  irq_attach (&proc_irq_sched, NULL, SCHED_PREEMPT_TIMER, 0);
+  irq_attach (&proc_irq_sched, NULL, SCHED_PREEMPT_TIMER, IRQ_INTERRUPT_SAFE);
 #endif
 
-  do_sched (&init->pdata.regs, &init->pd);
+  do_sched (init);
 }
diff --git a/kernel/sys/debug.h b/kernel/sys/debug.h
index c2fcf1b..9144e7f 100644
--- a/kernel/sys/debug.h
+++ b/kernel/sys/debug.h
@@ -1,11 +1,17 @@
 #ifndef _KERNEL_SYS_DEBUG_H
 #define _KERNEL_SYS_DEBUG_H
 
+#include <sys/smp.h>
+
 void debugprintf (const char* fmt, ...);
 
 #define DEBUG(fmt, ...)                                                                            \
   do {                                                                                             \
-    debugprintf ("%s: " fmt, __func__, ##__VA_ARGS__);                                             \
+    if (thiscpu != NULL) {                                                                         \
+      debugprintf ("(CPU %u) %s:%d: " fmt, thiscpu->id, __func__, __LINE__, ##__VA_ARGS__);        \
+    } else {                                                                                       \
+      debugprintf ("%s:%d: " fmt, __func__, __LINE__, ##__VA_ARGS__);                              \
+    }                                                                                              \
   } while (0)
 
 #endif // _KERNEL_SYS_DEBUG_H
diff --git a/kernel/sys/sched.h b/kernel/sys/sched.h
index 57c39d4..09254f4 100644
--- a/kernel/sys/sched.h
+++ b/kernel/sys/sched.h
@@ -1,8 +1,9 @@
 #ifndef _KERNEL_SYS_SCHED_H
 #define _KERNEL_SYS_SCHED_H
 
-#include <sys/mm.h>
+#include <libk/std.h>
+#include <proc/proc.h>
 
-void do_sched (void* regs, struct pd* pd);
+void do_sched (struct proc* proc);
 
 #endif // _KERNEL_SYS_SCHED_H
diff --git a/kernel/sys/syscall.h b/kernel/sys/syscall.h
new file mode 100644
index 0000000..3f5ca53
--- /dev/null
+++ b/kernel/sys/syscall.h
@@ -0,0 +1,6 @@
+#ifndef _KERNEL_SYS_SYSCALL_H
+#define _KERNEL_SYS_SYSCALL_H
+
+void syscall_init (void);
+
+#endif // _KERNEL_SYS_SYSCALL_H