MFi386: handle PSL_T properly across fork. Typo fix.

1 files changed, 13 insertions, 1 deletions

diff --git a/sys/amd64/amd64/vm_machdep.c b/sys/amd64/amd64/vm_machdep.c
index d784d02f80b2..9b9981234aef 100644
--- a/sys/amd64/amd64/vm_machdep.c
+++ b/sys/amd64/amd64/vm_machdep.c
@@ -57,6 +57,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/malloc.h>
 #include <sys/mbuf.h>
 #include <sys/mutex.h>
+#include <sys/pioctl.h>
 #include <sys/proc.h>
 #include <sys/sf_buf.h>
 #include <sys/smp.h>
@@ -133,6 +134,17 @@ cpu_fork(td1, p2, td2, flags)
 	td2->td_frame->tf_rdx = 1;
 
 	/*
+	 * If the parent process has the trap bit set (i.e. a debugger had
+	 * single stepped the process to the system call), we need to clear
+	 * the trap flag from the new frame unless the debugger had set PF_FORK
+	 * on the parent.  Otherwise, the child will receive a (likely
+	 * unexpected) SIGTRAP when it executes the first instruction after
+	 * returning  to userland.
+	 */
+	if ((p1->p_pfsflags & PF_FORK) == 0)
+		td2->td_frame->tf_rflags &= ~PSL_T;
+
+	/*
 	 * Set registers for trampoline to user mode.  Leave space for the
 	 * return address on stack.  These are the kernel mode register values.
 	 */
@@ -227,7 +239,7 @@ cpu_thread_setup(struct thread *td)
 
 /*
  * Initialize machine state (pcb and trap frame) for a new thread about to
- * upcall. Pu t enough state in the new thread's PCB to get it to go back 
+ * upcall. Put enough state in the new thread's PCB to get it to go back 
  * userret(), where we can intercept it again to set the return (upcall)
  * Address and stack, along with those from upcals that are from other sources
  * such as those generated in thread_userret() itself.