Bug 103000

Created attachment 134493 [details]
Client X errors and backtraces

Setup:
- Ubuntu 17.04 with Unity
- Latest X server built from git:
  git://anongit.freedesktop.org/git/xorg/xserver

Use-case:
- Boot

Expected output:
- Unity comes up like with earlier X server versions

Actual outcome:
- Desktop dies because unity-settings-daemon dies to X error

Notes:
- Backtraces attached, showing that issues is with X sync functionality
- Haven't seen this on machines with Ubuntu 16.04, but that could be just luck


Initial bisecting showed the issue to start between commits de3b618691 and d770f92932.

Manual review of the changes, showed few likely errors in following commit:
--------------------------------------------------
commit e0f872207aa203adb85e825c311ed50fe3a3af60
Author:     Eric Anholt <eric@anholt.net>
AuthorDate: Mon Sep 18 17:34:32 2017 -0700
Commit:     Adam Jackson <ajax@redhat.com>
CommitDate: Wed Sep 20 13:19:27 2017 -0400

    sync: Convert from "CARD64" to int64_t.
    
    The extension was using the name CARD64 to represent 64-bit values,
    with a #define from CARD64 to XSyncValue, a struct with a pair of
    32-bit values representing a signed 64-bit value.  This interfered
    with protocol headers using CARD64 to try to actually store a
    uint64_t.  Now that stdint.h exists, let's just use that here,
    instead.
    
    v2: Fix alarm delta changes.
    v3: Do the potentially overflowing math as uint and convert to int
        afterward, out of C spec paranoia.
    
    Signed-off-by: Eric Anholt <eric@anholt.net>
    Reviewed-by: Keith Packard <keithp@keithp.com>
--------------------------------------------------

At least following changes seem to be obviously wrong:
--------------------------------------------------
diff --git a/Xext/sync.c b/Xext/sync.c
...
@@ -655,16 +652,16 @@ SyncAwaitTriggerFired(SyncTrigger * pTrigger)
...
-            diffgreater = XSyncValueGreaterThan(diff, pAwait->event_threshold);
-            diffequal = XSyncValueEqual(diff, pAwait->event_threshold);
+            diffgreater = diff >= pAwait->event_threshold;
+            diffequal = diff == pAwait->event_threshold;
...
@@ -862,16 +859,13 @@ SyncChangeAlarmAttributes(ClientPtr client, SyncAlarm * pAlarm, Mask mask,
...
-             && XSyncValueGreaterThan(pAlarm->delta, zero))
+             && pAlarm->delta >= 0)
--------------------------------------------------