first version to support the FPU

- seems to work
- currently, we didn't support SIMD instructions

arch/x86/include/asm/tasks_types.h

@@ -55,11 +55,15 @@ typedef struct i387_fxsave_struct {
 	long	padding[56];
 } i387_fxsave_t __attribute__ ((aligned (16)));
 
-union fpu_union {
+union fpu_state {
 	i387_fsave_t	fsave;
 	i387_fxsave_t	fxsave;
 };
 
+static inline void save_fpu_state(union fpu_state* state) {
+	asm volatile ("fsave %0; fwait" : "=m"((*state).fsave));
+}
+
 #ifdef __cplusplus
 }
 #endif

arch/x86/kernel/entry.asm

@@ -64,16 +64,19 @@ ALIGN 4
 stublet:
 ; initialize stack pointer.
     mov esp, default_stack_pointer
-; enable cache and turn on FPU exceptions
     mov eax, cr0
-    ; enable cache
-    and eax, 0x9fffffff
-    ; ...and turn on FPU exceptions
-    or eax, 0x20
+; enable cache, disable paging and fpu emulation
+    and eax, 0x3ffffffb
+; ...monitor coprocessor and turn on FPU exceptions
+    or eax, 0x22
     mov cr0, eax
 ; clears the current pgd entry
     xor eax, eax
     mov cr3, eax
+; disable SSE support (TODO)
+    mov eax, cr4
+    and eax, 0xfffbf9ff
+    mov cr4, eax
 ; interpret multiboot information
     extern multiboot_init
     push ebx

arch/x86/kernel/isrs.c

@@ -74,6 +74,7 @@ extern void isr30(void);
 extern void isr31(void);
 
 static void fault_handler(struct state *s);
+static void fpu_handler(struct state *s);
 
 /* 
  * This is a very repetitive function... it's not hard, it's
@@ -158,6 +159,23 @@ void isrs_install(void)
 	// install the default handler
 	for(i=0; i<32; i++)
 		irq_install_handler(i, fault_handler);
+
+	// set hanlder for fpu exceptions
+	irq_uninstall_handler(7);
+	irq_install_handler(7, fpu_handler);
+}
+
+static void fpu_handler(struct state *s)
+{
+	task_t* task = per_core(current_task);
+
+	kputs("got FPU exception\n");
+	asm volatile ("clts"); // clear the TS flag of cr0
+	if (!task->fpu_used)  {
+		task->fpu_used = 1;
+		asm volatile ("finit");
+	} else 
+		asm volatile ("frstor %0" :: "m"(task->fpu.fsave)); // restore fpu state
 }
 
 /** @brief Exception messages
@@ -189,7 +207,7 @@ static void fault_handler(struct state *s)
 {
 	if (s->int_no < 32) {
 		kputs(exception_messages[s->int_no]);
-		kputs(" Exception.\n");
+		kprintf(" Exception. (%d)\n", s->int_no);
 		
 		/* Now, we signalize that we have handled the interrupt */
 		if (apic_is_enabled())

include/metalsvm/tasks_types.h

@@ -66,12 +66,14 @@ typedef struct task {
 	spinlock_t		vma_lock;
 	/// List of VMAs
 	vma_t*			vma_list;
+	/// Is set, when the FPU is used
+	uint32_t		fpu_used;
 	/// Mail inbox
 	mailbox_wait_msg_t	inbox;	
 	/// Mail outbox array
 	mailbox_wait_msg_t*	outbox[MAX_TASKS];
 	/// FPU state
-	union fpu_union		fpu_state;
+	union fpu_state		fpu;
 } __attribute__((packed))  task_t;
 
 #ifdef __cplusplus

kernel/tasks.c

@@ -48,7 +48,7 @@ DEFINE_PER_CORE(task_t*, current_task, NULL);
  * A task's id will be its position in this array.
  */
 static task_t task_table[MAX_TASKS] = {[0 ... MAX_TASKS-1] = {0, TASK_INVALID, ATOMIC_INIT(0), \
-			 SPINLOCK_INIT, NULL, SPINLOCK_INIT, NULL}};
+			 SPINLOCK_INIT, NULL, SPINLOCK_INIT, NULL, 0}};
 static spinlock_irqsave_t table_lock = SPINLOCK_IRQSAVE_INIT;
 
 /** @brief helper function for the assembly code to determine the current task
@@ -67,6 +67,7 @@ int multitasking_init(void) {
 		memset(task_table[0].outbox, 0x00, sizeof(mailbox_wait_msg_t*)*MAX_TASKS);
 		per_core(current_task) = task_table+0;
 		per_core(current_task)->pgd = get_boot_pgd();
+		task_table[0].fpu_used = 0;
 		return 0;
 	}
 
@@ -189,6 +190,7 @@ static int create_task(tid_t* id, entry_point_t ep, void* arg)
 
 			ret = create_default_frame(task_table+i, ep, arg);
 
+			task_table[i].fpu_used = 0;
 			task_table[i].status = TASK_READY;
 			break;
 		}
@@ -250,6 +252,7 @@ int sys_fork(void)
 			mailbox_wait_msg_init(&task_table[i].inbox);
 			memset(task_table[i].outbox, 0x00, sizeof(mailbox_wait_msg_t*)*MAX_TASKS);
 			task_table[i].outbox[per_core(current_task)->id] = &per_core(current_task)->inbox; 
+			task_table[i].fpu_used = 0x00;
 
 			ret = arch_fork(task_table+i);
 
@@ -707,7 +710,9 @@ void scheduler(void)
 			if (per_core(current_task)->status == TASK_RUNNING)
 				per_core(current_task)->status = TASK_READY;
 			task_table[new_id].status = TASK_RUNNING;
-	
+
+			if (per_core(current_task)->fpu_used)
+				save_fpu_state(&(per_core(current_task)->fpu));	
 			per_core(current_task) = task_table+new_id;
 			goto get_task_out;
 		}