File mozilla-bigendian_bit_flags_alias.patch of Package MozillaFirefox.9789

# HG changeset patch
# User Steve Fink <sfink@mozilla.com>
# Date 1536603384 25200
#      Mon Sep 10 11:16:24 2018 -0700
# Node ID 510eb23f4e213733136e875e11a48c5acf463792
# Parent  c7cfa9a530264a25b095f0da337e035051e5075e
# EXP-Topic b1488552.enD
Bug 1488552 - JSString flags bit must alias the low 32 bits of JSObject.group_, not the high 32. r=tcampbell

diff --git a/js/src/gc/Marking-inl.h b/js/src/gc/Marking-inl.h
--- a/js/src/gc/Marking-inl.h
+++ b/js/src/gc/Marking-inl.h
@@ -87,20 +87,20 @@ MaybeForwarded(T t)
 }
 
 inline void
 RelocationOverlay::forwardTo(Cell* cell)
 {
     MOZ_ASSERT(!isForwarded());
     // The location of magic_ is important because it must never be valid to see
     // the value Relocated there in a GC thing that has not been moved.
-    static_assert(offsetof(RelocationOverlay, magic_) == offsetof(JSObject, group_) + sizeof(uint32_t),
-                  "RelocationOverlay::magic_ is in the wrong location");
-    static_assert(offsetof(RelocationOverlay, magic_) == offsetof(js::Shape, base_) + sizeof(uint32_t),
-                  "RelocationOverlay::magic_ is in the wrong location");
+    //static_assert(offsetof(RelocationOverlay, magic_) == offsetof(JSObject, group_) + sizeof(uint32_t),
+    //              "RelocationOverlay::magic_ is in the wrong location");
+    //static_assert(offsetof(RelocationOverlay, magic_) == offsetof(js::Shape, base_) + sizeof(uint32_t),
+    //              "RelocationOverlay::magic_ is in the wrong location");
     static_assert(offsetof(RelocationOverlay, magic_) == offsetof(JSString, d.u1.length),
                   "RelocationOverlay::magic_ is in the wrong location");
     magic_ = Relocated;
     newLocation_ = cell;
 }
 
 #ifdef JSGC_HASH_TABLE_CHECKS
 
diff --git a/js/src/gc/RelocationOverlay.h b/js/src/gc/RelocationOverlay.h
--- a/js/src/gc/RelocationOverlay.h
+++ b/js/src/gc/RelocationOverlay.h
@@ -29,24 +29,35 @@ struct Cell;
  * This structure overlays a Cell that has been moved and provides a way to find
  * its new location. It's used during generational and compacting GC.
  */
 class RelocationOverlay
 {
     /* See comment in js/public/HeapAPI.h. */
     static const uint32_t Relocated = js::gc::Relocated;
 
+#if MOZ_LITTLE_ENDIAN
     /*
-     * Keep the low 32 bits untouched. Use them to distinguish strings from
+     * Keep the first 32 bits untouched. Use them to distinguish strings from
      * objects in the nursery.
      */
     uint32_t preserve_;
 
     /* Set to Relocated when moved. */
     uint32_t magic_;
+#elif JS_BITS_PER_WORD == 64
+    /*
+     * On big-endian, we need to reorder to keep preserve_ lined up with the
+     * low 32 bits of the aligned group_ pointer in JSObject.
+     */
+    uint32_t magic_;
+    uint32_t preserve_;
+#else
+#  error "Support for 32-bit big-endian architectures is untested. See bug 1488552."
+#endif
 
     /* The location |this| was moved to. */
     Cell* newLocation_;
 
     /* A list entry to track all relocated things. */
     RelocationOverlay* next_;
 
   public:
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -635,18 +635,25 @@ struct Function {
 struct String
 {
     static const uint32_t NON_ATOM_BIT     = JS_BIT(0);
     static const uint32_t LINEAR_BIT       = JS_BIT(1);
     static const uint32_t INLINE_CHARS_BIT = JS_BIT(3);
     static const uint32_t LATIN1_CHARS_BIT = JS_BIT(6);
     static const uint32_t EXTERNAL_FLAGS   = LINEAR_BIT | NON_ATOM_BIT | JS_BIT(5);
     static const uint32_t TYPE_FLAGS_MASK  = JS_BIT(6) - 1;
+#if MOZ_LITTLE_ENDIAN
     uint32_t flags;
     uint32_t length;
+#elif JS_BITS_PER_WORD == 64
+    uint32_t length;
+    uint32_t flags;
+#else
+#  error "Support for 32-bit big-endian architectures is untested. See bug 1488552."
+#endif
     union {
         const JS::Latin1Char* nonInlineCharsLatin1;
         const char16_t* nonInlineCharsTwoByte;
         JS::Latin1Char inlineStorageLatin1[1];
         char16_t inlineStorageTwoByte[1];
     };
     const JSStringFinalizer* externalFinalizer;
 
diff --git a/js/src/vm/StringType.h b/js/src/vm/StringType.h
--- a/js/src/vm/StringType.h
+++ b/js/src/vm/StringType.h
@@ -2,16 +2,17 @@
  * vim: set ts=8 sts=4 et sw=4 tw=99:
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef vm_StringType_h
 #define vm_StringType_h
 
+#include "mozilla/EndianUtils.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/PodOperations.h"
 #include "mozilla/Range.h"
 
 #include "jsapi.h"
 #include "jsfriendapi.h"
 
 #include "builtin/String.h"
@@ -161,18 +162,30 @@ class JSString : public js::gc::Cell
     static const size_t NUM_INLINE_CHARS_LATIN1   = 2 * sizeof(void*) / sizeof(JS::Latin1Char);
     static const size_t NUM_INLINE_CHARS_TWO_BYTE = 2 * sizeof(void*) / sizeof(char16_t);
 
     /* Fields only apply to string types commented on the right. */
     struct Data
     {
         union {
             struct {
+#if MOZ_LITTLE_ENDIAN
                 uint32_t           flags;               /* JSString */
                 uint32_t           length;              /* JSString */
+#elif JS_BITS_PER_WORD == 64
+                /*
+                 * On big-endian, we need to reorder to keep flags lined up
+                 * with the low 32 bits of the aligned group_ pointer in
+                 * JSObject.
+                 */
+                uint32_t           length;              /* JSString */
+                uint32_t           flags;               /* JSString */
+#else
+#  error "Support for 32-bit big-endian architectures is untested. See bug 1488552."
+#endif
             };
             uintptr_t              flattenData;         /* JSRope (temporary while flattening) */
         } u1;
         union {
             union {
                 /* JS(Fat)InlineString */
                 JS::Latin1Char     inlineStorageLatin1[NUM_INLINE_CHARS_LATIN1];
                 char16_t           inlineStorageTwoByte[NUM_INLINE_CHARS_TWO_BYTE];