kernel: trap-dependent state restore, trace fixes

. restore state depends on how saving of state was done;
	  also remember trap style in sig context
	. actually set and restore TRACEBIT with new trap styles;
	  have to remove it once process enters kernel though, done
	  in debug trap exception handler
	. introduce MF_STEP that makes arch-specific code
	  turn on trace bit instead of setting TRACEBIT directly,
	  a bit more arch-friendly and avoids keeping precious
	  state in per-process PSW arch-dependently

kernel/arch/arm/arch_system.c

@@ -48,7 +48,8 @@ void arch_proc_reset(struct proc *pr)
         	pr->p_reg.psr = INIT_PSR;
 }
 
-void arch_proc_setcontext(struct proc *p, struct stackframe_s *state, int isuser)
+void arch_proc_setcontext(struct proc *p, struct stackframe_s *state,
+	int isuser, int trapstyle)
 {
 }
 

kernel/arch/i386/arch_system.c

@@ -182,7 +182,7 @@ void arch_proc_reset(struct proc *pr)
 	pr->p_reg.ds = USER_DS_SELECTOR;
 
 	/* set full context and make sure it gets restored */
-	arch_proc_setcontext(pr, &reg, 0);
+	arch_proc_setcontext(pr, &reg, 0, KTS_FULLCONTEXT);
 }
 
 void arch_set_secondary_ipc_return(struct proc *p, u32_t val)
@@ -511,14 +511,21 @@ struct proc * arch_finish_switch_to_user(void)
 	*((reg_t *)stk) = (reg_t) p;
 
 	/* make sure IF is on in FLAGS so that interrupts won't be disabled
-	 * once p's context is restored. this should not be possible.
+	 * once p's context is restored.
 	 */
-        assert(p->p_reg.psw & (1L << 9));
+        p->p_reg.psw |= IF_MASK;
+
+	/* Set TRACEBIT state properly. */
+	if(p->p_misc_flags & MF_STEP)
+        	p->p_reg.psw |= TRACEBIT;
+	else
+        	p->p_reg.psw &= ~TRACEBIT;
 
 	return p;
 }
 
-void arch_proc_setcontext(struct proc *p, struct stackframe_s *state, int isuser)
+void arch_proc_setcontext(struct proc *p, struct stackframe_s *state,
+	int isuser, int trap_style)
 {
 	if(isuser) {
 		/* Restore user bits of psw from sc, maintain system bits
@@ -555,7 +562,7 @@ void arch_proc_setcontext(struct proc *p, struct stackframe_s *state, int isuser
 	}
 	if(p->p_seg.p_kern_trap_style == KTS_NONE)
 		printf("WARNINIG: setting full context of out-of-kernel process\n");
-	p->p_seg.p_kern_trap_style = KTS_FULLCONTEXT;
+	p->p_seg.p_kern_trap_style = trap_style;
 }
 
 void restore_user_context(struct proc *p)
@@ -666,4 +673,3 @@ static void ser_init(void)
 	outb(COM1_LCR, lcr);
 }
 #endif
-

kernel/arch/i386/exception.c

@@ -228,6 +228,26 @@ void exception_handler(int is_nested, struct exception_frame * frame)
 		frame->eip = (reg_t) __frstor_failure;
 		return;
 	}
+
+  	if(frame->vector == DEBUG_VECTOR
+		&& (saved_proc->p_reg.psw & TRACEBIT)
+		&& (saved_proc->p_seg.p_kern_trap_style == KTS_NONE)) {
+		/* Getting a debug trap in the kernel is legitimate
+		 * if a traced process entered the kernel using sysenter
+		 * or syscall; the trap flag is not cleared then.
+		 *
+		 * It triggers on the first kernel entry so the trap
+		 * style is still KTS_NONE.
+		 */
+
+		frame->eflags &= ~TRACEBIT;
+
+		return;
+
+		/* If control passes, this case is not recognized as legitimate
+		 * and we panic later on after all.
+		 */
+	}
   }
 
   if(frame->vector == PAGE_FAULT_VECTOR) {

kernel/arch/i386/mpx.S

@@ -240,6 +240,11 @@ syscall_sysenter_common:
 	mov	%esi, SPREG(%ebp)	/* esi is return esp */
 	mov	%edx, PCREG(%ebp)	/* edx is return eip */
 
+	/* save PSW */
+	pushf
+	pop	%edx
+	mov	%edx, PSWREG(%ebp)
+
 	/* check for call type; do_ipc? */
 	cmp	$IPCVEC_UM, %edi
 	jz	ipc_entry_common
@@ -396,6 +401,7 @@ ENTRY(restore_user_context_sysenter)
 	mov	SPREG(%ebp), %ecx	/* sysexit restores ESP using ECX */
 	mov	AXREG(%ebp), %eax	/* trap return value */
 	mov	BXREG(%ebp), %ebx	/* secondary return value */
+	movl	PSWREG(%ebp), %edi	/* load desired PSW to EDI */
 	sti				/* enable interrupts */
 	sysexit				/* jump to EIP in user */
 
@@ -410,6 +416,7 @@ ENTRY(restore_user_context_syscall)
 	mov	SPREG(%ebp), %esp	/* restore ESP directly */
 	mov	AXREG(%ebp), %eax	/* trap return value */
 	mov	BXREG(%ebp), %ebx	/* secondary return value */
+	movl	PSWREG(%ebp), %edi	/* load desired PSW to EDI */
 	sysret				/* jump to EIP in user */
 
 ENTRY(restore_user_context_int)

kernel/arch/i386/usermapped_glo_ipc.S

@@ -35,6 +35,8 @@ ENTRY(usermapped_ ## name ## _sysenter)					;\
 	SETARGS			/* call-specific register setup */	;\
 	sysenter		/* disappear into kernel */		;\
 0:									;\
+	push	%edi		/* kernel has desired PSW in %edi */	;\
+	popf			/* set PSW kernel wants us to have */	;\
 	mov	%ebx, %ecx	/* return w. state mangled; save %ebx */;\
 	pop	%edi							;\
 	pop	%esi							;\
@@ -59,6 +61,8 @@ ENTRY(usermapped_ ## name ## _syscall)					;\
 	SETARGS			/* call-specific register setup */	;\
 	movl	%ecx, %edx	/* %ecx is clobbered by SYSCALL */	;\
 	syscall			/* disappear into kernel */		;\
+	push	%edi		/* kernel has desired PSW in %edi */	;\
+	popf			/* set PSW kernel wants us to have */	;\
 	mov	%ebx, %ecx	/* return w. state mangled; save %ebx */;\
 	pop	%edi							;\
 	pop	%esi							;\