From f3079e509c5cf60042ae2261499ee13b6b02498a Mon Sep 17 00:00:00 2001
From: Adam Jackson <ajax@redhat.com>
Date: Thu, 6 Feb 2020 13:45:35 -0500
Subject: [PATCH] xt: Work around a compiler issue with gcc 10

GRABEXT() is used to look up a pointer that sometimes lives just past
the end of an XtServerGrabRec. Whether it's really there or not depends
on XtServerGrabRec::hasExt. In a couple of places, we build those
structs on the stack and pass them to other functions; such structs
always have hasExt == 0, so GRABEXT would never get called in practice.
However, there exists a bug in gcc 10 - more or less difficult to hit,
depending on your compiler options and architecture - where it would not
notice that the dereference after GRABEXT is dead code, at which point
it looks like you're dereferencing one past the end of the array, which
is illegal, and you you get:

    PassivGrab.c:292:35: error: array subscript 0 is outside array bounds
    of 'XtServerGrabRec[1]' {aka 'struct _XtServerGrabRec[1]'}
    [-Werror=array-bounds]

As a completely stupid workaround, build those on-stack structs as
arrays of two, so that the (dead) dereference looks like it's pointing
into the dummy member of the array. This is almost certainly a compiler
bug and I don't encourage merging this patch upstream, but if you need
to build libXt with gcc 10 absolutely right this second, here it is.

For details on the gcc issue, see:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93582
---
 src/PassivGrab.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/PassivGrab.c b/src/PassivGrab.c
index bece0d9..b174d40 100644
--- a/src/PassivGrab.c
+++ b/src/PassivGrab.c
@@ -553,7 +553,7 @@ XtServerGrabPtr _XtCheckServerGrabsOnWidget (
     _XtBoolean		isKeyboard)
 {
     register XtServerGrabPtr grab;
-    XtServerGrabRec 	tempGrab;
+    XtServerGrabRec 	tempGrab[2];
     XtServerGrabPtr	*passiveListPtr;
     XtPerWidgetInput	pwi;
 
@@ -577,13 +577,13 @@ XtServerGrabPtr _XtCheckServerGrabsOnWidget (
     /* Take only the lower thirteen bits as modifier state.  The X Keyboard
      * Extension may be representing keyboard group state in two upper bits.
      */
-    tempGrab.widget = widget;
-    tempGrab.keybut = (KeyCode) event->xkey.keycode; /* also xbutton.button */
-    tempGrab.modifiers = event->xkey.state & 0x1FFF; /*also xbutton.state*/
-    tempGrab.hasExt = False;
+    tempGrab[0].widget = widget;
+    tempGrab[0].keybut = (KeyCode) event->xkey.keycode; /* also xbutton.button */
+    tempGrab[0].modifiers = event->xkey.state & 0x1FFF; /*also xbutton.state*/
+    tempGrab[0].hasExt = False;
 
     for (grab = *passiveListPtr; grab; grab = grab->next) {
-	if (GrabMatchesSecond(&tempGrab, grab))
+	if (GrabMatchesSecond(tempGrab, grab))
 	    return (grab);
     }
     return (XtServerGrabPtr)NULL;
@@ -775,17 +775,17 @@ void   UngrabKeyOrButton (
     Modifiers	modifiers,
     Boolean	isKeyboard)
 {
-    XtServerGrabRec 	tempGrab;
+    XtServerGrabRec 	tempGrab[2];
     XtPerWidgetInput	pwi;
 
     XtCheckSubclass(widget, coreWidgetClass,
 		    "in XtUngrabKey or XtUngrabButton");
 
     /* Build a temporary grab list entry */
-    tempGrab.widget = widget;
-    tempGrab.modifiers = (unsigned short) modifiers;
-    tempGrab.keybut = (KeyCode) keyOrButton;
-    tempGrab.hasExt = False;
+    tempGrab[0].widget = widget;
+    tempGrab[0].modifiers = (unsigned short) modifiers;
+    tempGrab[0].keybut = (KeyCode) keyOrButton;
+    tempGrab[0].hasExt = False;
 
     LOCK_PROCESS;
     pwi = _XtGetPerWidgetInput(widget, FALSE);
@@ -817,7 +817,7 @@ void   UngrabKeyOrButton (
 
     /* Delete all entries which are encompassed by the specified grab. */
     DeleteServerGrabFromList(isKeyboard ? &pwi->keyList : &pwi->ptrList,
-			     &tempGrab);
+			     tempGrab);
 }
 
 void  XtGrabKey (
-- 
2.23.0