commit f326d68d762edf4b0e9604daa446b6f8ca25725a
Author: Mark Wielaard <mark@klomp.org>
Date:   Sun Jul 26 22:40:22 2020 +0200

    epoll_ctl warns for uninitialized padding on non-amd64 64bit arches
    
    struct vki_epoll_event is packed on x86_64, but not on other 64bit
    arches. This means that on 64bit arches there can be padding in the
    epoll_event struct. Seperately the data field is only used by user
    space (which might not set the data field if it doesn't need to).
    
    Only check the events field on epoll_ctl. But assume both events
    and data are both written to by epoll_[p]wait (exclude padding).
    
    https://bugs.kde.org/show_bug.cgi?id=422623

diff --git a/coregrind/m_syswrap/syswrap-linux.c b/coregrind/m_syswrap/syswrap-linux.c
index 5b5b7eee6..929a4d9af 100644
--- a/coregrind/m_syswrap/syswrap-linux.c
+++ b/coregrind/m_syswrap/syswrap-linux.c
@@ -2099,8 +2099,29 @@ PRE(sys_epoll_ctl)
          SARG1, ( ARG2<3 ? epoll_ctl_s[ARG2] : "?" ), SARG3, ARG4);
    PRE_REG_READ4(long, "epoll_ctl",
                  int, epfd, int, op, int, fd, struct vki_epoll_event *, event);
-   if (ARG2 != VKI_EPOLL_CTL_DEL)
-      PRE_MEM_READ( "epoll_ctl(event)", ARG4, sizeof(struct vki_epoll_event) );
+   if (ARG2 != VKI_EPOLL_CTL_DEL) {
+      /* Just check the events field, the data field is for user space and
+         unused by the kernel.  */
+      struct vki_epoll_event *event = (struct vki_epoll_event *) ARG4;
+      PRE_MEM_READ( "epoll_ctl(event)", (Addr) &event->events,
+                    sizeof(__vki_u32) );
+   }
+}
+
+/* RES event records have been written (exclude padding).  */
+static void epoll_post_helper ( ThreadId tid, SyscallArgs* arrghs,
+                                SyscallStatus* status )
+{
+   vg_assert(SUCCESS);
+   if (RES > 0) {
+      Int i;
+      struct vki_epoll_event **events = (struct vki_epoll_event**)(Addr)ARG2;
+      for (i = 0; i < RES; i++) {
+         /* Assume both events and data are set (data is user space only). */
+         POST_FIELD_WRITE(events[i]->events);
+         POST_FIELD_WRITE(events[i]->data);
+      }
+   }
 }
 
 PRE(sys_epoll_wait)
@@ -2111,13 +2132,12 @@ PRE(sys_epoll_wait)
    PRE_REG_READ4(long, "epoll_wait",
                  int, epfd, struct vki_epoll_event *, events,
                  int, maxevents, int, timeout);
+   /* Assume all (maxevents) events records should be (fully) writable. */
    PRE_MEM_WRITE( "epoll_wait(events)", ARG2, sizeof(struct vki_epoll_event)*ARG3);
 }
 POST(sys_epoll_wait)
 {
-   vg_assert(SUCCESS);
-   if (RES > 0)
-      POST_MEM_WRITE( ARG2, sizeof(struct vki_epoll_event)*RES ) ;
+   epoll_post_helper (tid, arrghs, status);
 }
 
 PRE(sys_epoll_pwait)
@@ -2130,15 +2150,14 @@ PRE(sys_epoll_pwait)
                  int, epfd, struct vki_epoll_event *, events,
                  int, maxevents, int, timeout, vki_sigset_t *, sigmask,
                  vki_size_t, sigsetsize);
+   /* Assume all (maxevents) events records should be (fully) writable. */
    PRE_MEM_WRITE( "epoll_pwait(events)", ARG2, sizeof(struct vki_epoll_event)*ARG3);
    if (ARG5)
       PRE_MEM_READ( "epoll_pwait(sigmask)", ARG5, sizeof(vki_sigset_t) );
 }
 POST(sys_epoll_pwait)
 {
-   vg_assert(SUCCESS);
-   if (RES > 0)
-      POST_MEM_WRITE( ARG2, sizeof(struct vki_epoll_event)*RES ) ;
+   epoll_post_helper (tid, arrghs, status);
 }
 
 PRE(sys_eventfd)