File xen.3fd3b266d4198c06e8e421ca515d9ba09ccd5155.patch of Package xen

From: Jan Beulich <jbeulich@suse.com>
Date: Mon, 13 May 2019 09:51:23 +0200
Subject: 3fd3b266d4198c06e8e421ca515d9ba09ccd5155
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trace: fix build with gcc9

While I've not observed this myself, gcc 9 (imo validly) reportedly may
complain

trace.c: In function '__trace_hypercall':
trace.c:826:19: error: taking address of packed member of 'struct <anonymous>' may result in an unaligned pointer value [-Werror=address-of-packed-member]
  826 |     uint32_t *a = d.args;

and the fix is rather simple - remove the __packed attribute. Introduce
a BUILD_BUG_ON() as replacement, for the unlikely case that Xen might
get ported to an architecture where array alignment higher that that of
its elements.

Reported-by: Martin Liška <martin.liska@suse.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>
---
 xen/common/trace.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/xen/common/trace.c
+++ b/xen/common/trace.c
@@ -814,30 +814,36 @@ unlock:
     spin_unlock_irqrestore(&this_cpu(t_lock), flags);
 
     /* Notify trace buffer consumer that we've crossed the high water mark. */
     if ( likely(buf!=NULL)
          && started_below_highwater
          && (calc_unconsumed_bytes(buf) >= t_buf_highwater) )
         tasklet_schedule(&trace_notify_dom0_tasklet);
 }
 
 void __trace_hypercall(uint32_t event, unsigned long op,
                        const xen_ulong_t *args)
 {
-    struct __packed {
+    struct {
         uint32_t op;
         uint32_t args[6];
     } d;
     uint32_t *a = d.args;
 
+    /*
+     * In lieu of using __packed above, which gcc9 legitimately doesn't
+     * like in combination with the address of d.args[] taken.
+     */
+    BUILD_BUG_ON(offsetof(typeof(d), args) != sizeof(d.op));
+
 #define APPEND_ARG32(i)                         \
     do {                                        \
         unsigned i_ = (i);                      \
         *a++ = args[(i_)];                      \
         d.op |= TRC_PV_HYPERCALL_V2_ARG_32(i_); \
     } while( 0 )
 
     /*
      * This shouldn't happen as @op should be small enough but just in
      * case, warn if the argument bits in the trace record would
      * clobber the hypercall op.
      */