kernel: Save floating-point environment when switching in and out of userspace threads

kernel/src/arch/x86_64/CPU.cpp

@@ -23,6 +23,18 @@ extern void pic_eoi(unsigned char irq);
 extern void pic_eoi(Registers* regs);
 extern void setup_idt();
 
+void FPData::save()
+{
+    asm volatile("fxsave (%0)" : : "r"(m_data));
+    m_already_saved = true;
+}
+
+void FPData::restore()
+{
+    if(!m_already_saved) return;
+    asm volatile("fxrstor (%0)" : : "r"(m_data));
+}
+
 // Interrupt handling
 
 #define FIXME_UNHANDLED_INTERRUPT(name)                                                                                \

kernel/src/arch/x86_64/CPU.h

@@ -9,6 +9,16 @@ struct Registers // Saved CPU registers for x86-64
     u64 rip, cs, rflags, rsp, ss;
 };
 
+struct FPData
+{
+    void save();
+    void restore();
+
+  private:
+    char m_data[512] alignas(16);
+    bool m_already_saved;
+};
+
 struct [[gnu::packed]] TSS
 {
     u32 reserved0;

kernel/src/thread/Scheduler.cpp

@@ -219,10 +219,12 @@ namespace Scheduler
         if (old_thread != new_thread)
         {
             switch_context(old_thread, new_thread, regs);
+            if (!old_thread->is_kernel) old_thread->fp_data.save();
             if (!new_thread->is_kernel)
             {
                 MMU::switch_page_directory(new_thread->directory);
                 CPU::switch_kernel_stack(new_thread->kernel_stack.top());
+                new_thread->fp_data.restore();
             }
         }
 

kernel/src/thread/Thread.h

@@ -21,8 +21,6 @@ enum class ThreadState
     Dying
 };
 
-// FIXME: Save floating point state. (SSE registers on x86_64 using FXSAVE and FXRSTOR)
-
 struct Thread : public LinkedListNode<Thread>
 {
     Registers regs;
@@ -41,6 +39,8 @@ struct Thread : public LinkedListNode<Thread>
 
     OwnedPtr<UserVM> vm_allocator;
 
+    FPData fp_data;
+
     ThreadState state = ThreadState::Runnable;
 
     bool is_kernel { true };