Clear thread pflags in _do_execve (#1394)

* sys/kern/exec.c: clear pflags right after mcontext_init
* include/sys/thread.h: add comment for TDP_* flags

Author: panantoni01

include/sys/thread.h

@@ -70,6 +70,8 @@ typedef enum {
 } td_flags_t;
 
 typedef enum {
+  /* After user context setup in execve TDP_* flags that should not be inherited
+   * should be cleared */
   TDP_OLDSIGMASK = 0x01,  /* Pass td_oldsigmask as return mask to send_sig(). */
   TDP_FPUCTXSAVED = 0x02, /* FPU context was saved by `ctx_switch`. */
   TDP_FPUINUSE = 0x04     /* FPU is in use and its context should be saved &

sys/kern/exec.c

@@ -411,6 +411,9 @@ static int _do_execve(exec_args_t *args) {
   /* Set up user context. */
   mcontext_init(td->td_uctx, (void *)eh.e_entry, (void *)stack_top);
 
+  /* All thread pflags that should not be inherited should be cleared */
+  td->td_pflags = 0;
+
   WITH_PROC_LOCK(p) {
     sig_onexec(p);
     /* Set new credentials if needed */