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-rw-r--r--kernel/trap.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/kernel/trap.c b/kernel/trap.c
index 06fc4b3..835a3b0 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -37,7 +37,7 @@ void
usertrap(void)
{
int which_dev = 0;
-
+
if((r_sstatus() & SSTATUS_SPP) != 0)
panic("usertrap: not from user mode");
@@ -49,8 +49,6 @@ usertrap(void)
// save user program counter.
p->tf->epc = r_sepc();
-
- intr_on();
if(r_scause() == 8){
// system call
@@ -59,11 +57,15 @@ usertrap(void)
// but we want to return to the next instruction.
p->tf->epc += 4;
+ // an interrupt will change sstatus &c registers,
+ // so don't enable until done with those registers.
+ intr_on();
+
syscall();
} else if((which_dev = devintr()) != 0){
// ok
} else {
- printf("usertrap(): unexpected scause 0x%p pid=%d\n", r_scause(), p->pid);
+ printf("usertrap(): unexpected scause %p pid=%d\n", r_scause(), p->pid);
printf(" sepc=%p stval=%p\n", r_sepc(), r_stval());
p->killed = 1;
}