Differentiate syscall handler by number.

This causes us to panic on the unhandled exit syscall.

zion/CMakeLists.txt

@@ -11,6 +11,7 @@ add_executable(zion
   memory/paging_util.cpp
   memory/physical_memory.cpp
   scheduler/context_switch.s
+  scheduler/jump_user_space.s
   scheduler/process.cpp
   scheduler/scheduler.cpp
   scheduler/thread.cpp

zion/common/gdt.cpp

@@ -90,3 +90,5 @@ void InitGdt() {
       "ltr %%ax;" ::
           : "rax");
 }
+
+void SetRsp0(uint64_t rsp0) { gTaskStateSegment.rsp0 = rsp0; }

zion/common/gdt.h

@@ -1,3 +1,7 @@
 #pragma once
 
+#include <stdint.h>
+
 void InitGdt();
+
+void SetRsp0(uint64_t rsp0);

zion/loader/elf_loader.cpp

@@ -56,7 +56,7 @@ void badmemcpy(uint64_t base, uint64_t offset, uint64_t dest) {
 
 }  // namespace
 
-void LoadElfProgram(uint64_t base, uint64_t offset) {
+uint64_t LoadElfProgram(uint64_t base, uint64_t offset) {
   Elf64Header* header = reinterpret_cast<Elf64Header*>(base);
   dbgln("phoff: %u phnum: %u", header->phoff, header->phnum);
   Elf64ProgramHeader* programs =
@@ -71,4 +71,5 @@ void LoadElfProgram(uint64_t base, uint64_t offset) {
     EnsureResident(program.vaddr, program.memsz);
     badmemcpy(base + program.offset, program.filesz, program.vaddr);
   }
+  return header->entry;
 }

zion/loader/elf_loader.h

@@ -2,4 +2,5 @@
 
 #include <stdint.h>
 
-void LoadElfProgram(uint64_t base, uint64_t length);
+// Loads the elf program and returns its entry point.
+uint64_t LoadElfProgram(uint64_t base, uint64_t length);

zion/memory/paging_util.cpp

@@ -6,6 +6,7 @@
 
 #define PRESENT_BIT 0x1
 #define READ_WRITE_BIT 0x2
+#define USER_MODE_BIT 0x4;
 #define SIGN_EXT 0xFFFF0000'00000000
 #define RECURSIVE ((uint64_t)0x1FE)
 #define PML_OFFSET 39
@@ -79,23 +80,29 @@ void MapPage(uint64_t virt, uint64_t phys) {
     panic("Allocating Over Existing Page: %m", virt);
   }
 
+  uint64_t access_bits = PRESENT_BIT | READ_WRITE_BIT;
+  uint64_t higher_half = 0xffff8000'00000000;
+  if ((virt & higher_half) != higher_half) {
+    access_bits |= USER_MODE_BIT;
+  }
+
   if (!PageDirectoryPointerLoaded(virt)) {
     uint64_t page = phys_mem::AllocatePage();
-    *Pml4Entry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    *Pml4Entry(virt) = page | access_bits;
     ZeroOutPage(PageDirectoryPointerEntry(virt));
   }
   if (!PageDirectoryLoaded(virt)) {
     uint64_t page = phys_mem::AllocatePage();
-    *PageDirectoryPointerEntry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    *PageDirectoryPointerEntry(virt) = page | access_bits;
     ZeroOutPage(PageDirectoryEntry(virt));
   }
   if (!PageTableLoaded(virt)) {
     uint64_t page = phys_mem::AllocatePage();
-    *PageDirectoryEntry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    *PageDirectoryEntry(virt) = page | access_bits;
     ZeroOutPage(PageTableEntry(virt));
   }
 
-  *PageTableEntry(virt) = PageAlign(phys) | PRESENT_BIT | READ_WRITE_BIT;
+  *PageTableEntry(virt) = PageAlign(phys) | access_bits;
   ZeroOutPage(reinterpret_cast<uint64_t*>(virt));
 }
 

zion/scheduler/jump_user_space.s

@@ -0,0 +1,16 @@
+.global jump_user_space
+// rdi - entry point, rsi - user stack
+jump_user_space:
+  cli
+  mov $0x23, %ax
+  mov %ax, %ds
+  mov %ax, %es
+  mov %ax, %fs
+  mov %ax, %gs
+
+  pushq $0x23 # ss
+  pushq %rsi
+  pushf  # Can we just push 0 for flags?
+  pushq $0x1B # cs
+  pushq %rdi
+  iretq

zion/scheduler/thread.cpp

@@ -1,12 +1,16 @@
 #include "scheduler/thread.h"
 
+#include "common/gdt.h"
 #include "debug/debug.h"
 #include "loader/elf_loader.h"
+#include "memory/paging_util.h"
 #include "scheduler/process.h"
 #include "scheduler/scheduler.h"
 
 namespace {
 
+extern "C" void jump_user_space(uint64_t rip, uint64_t rsp);
+
 extern "C" void thread_init() {
   asm("sti");
   sched::CurrentThread().Init();
@@ -36,9 +40,10 @@ Thread::Thread(Process* proc, uint64_t tid, uint64_t elf_ptr)
 uint64_t Thread::pid() { return process_->id(); }
 
 void Thread::Init() {
-  LoadElfProgram(elf_ptr_, 0);
-  while (true) {
-    dbgln("[%u.%u]", pid(), id_);
-    sched::Yield();
-  }
+  dbgln("[%u.%u]", pid(), id_);
+  uint64_t rip = LoadElfProgram(elf_ptr_, 0);
+  uint64_t rsp = 0x80000000;
+  EnsureResident(rsp - 1, 1);
+  SetRsp0(rsp0_start_);
+  jump_user_space(rip, rsp);
 }

zion/syscall/syscall.cpp

@@ -3,6 +3,7 @@
 #include <stdint.h>
 
 #include "debug/debug.h"
+#include "include/zcall.h"
 #include "scheduler/scheduler.h"
 
 #define EFER 0xC0000080
@@ -53,5 +54,12 @@ void InitSyscall() {
 }
 
 extern "C" void SyscallHandler(uint64_t call_id, char* message) {
-  dbgln(message);
+  Thread& thread = sched::CurrentThread();
+  switch (call_id) {
+    case Z_DEBUG_PRINT:
+      dbgln("[%u.%u] %s", thread.pid(), thread.tid(), message);
+      break;
+    default:
+      panic("Unhandled syscall number: %u", call_id);
+  }
 }