Changeset 247281 in webkit

Timestamp:

Jul 9, 2019 2:49:21 PM (5 years ago)

Author:

commit-queue@webkit.org

Message:

WKObject's minimum object alignment needs to be larger
​https://bugs.webkit.org/show_bug.cgi?id=199523

Patch by Saagar Jha <​saagarjha@apple.com> on 2019-07-09
Reviewed by Alex Christensen.

WKObject's wrapped objects are currently constructed at addresses aligned to 8-byte boundaries, but some
classes have more stringent requirements. By querying std::aligned_storage for the alignment of an object
larger than anything we can construct, we should be able to satisfy alignment for any of WebKit's types.

• Shared/Cocoa/APIObject.mm: Use std::aligned_storage in conjunction with alignof to determine

minimumObjectAlignment, instead of hardcoding 8.

Location:

trunk/Source/WebKit

Files:

• ChangeLog (modified) (1 diff)
• Shared/Cocoa/APIObject.mm (modified) (1 diff)

trunk/Source/WebKit/ChangeLog

@@ +1 @@
+2019-07-09  Saagar Jha  <saagarjha@apple.com>
+
+        WKObject's minimum object alignment needs to be larger
+        https://bugs.webkit.org/show_bug.cgi?id=199523
+
+        Reviewed by Alex Christensen.
+
+        WKObject's wrapped objects are currently constructed at addresses aligned to 8-byte boundaries, but some
+        classes have more stringent requirements. By querying std::aligned_storage for the alignment of an object
+        larger than anything we can construct, we should be able to satisfy alignment for any of WebKit's types.
+
+        * Shared/Cocoa/APIObject.mm: Use std::aligned_storage in conjunction with alignof to determine
+        minimumObjectAlignment, instead of hardcoding 8.
+
 2019-07-09  Megan Gardner  <megan_gardner@apple.com>
 

trunk/Source/WebKit/Shared/Cocoa/APIObject.mm

@@ -91 +91 @@
 #endif
 
-static const size_t minimumObjectAlignment = 8;
+static const size_t minimumObjectAlignment = alignof(std::aligned_storage<std::numeric_limits<size_t>::max()>::type);
 static_assert(minimumObjectAlignment >= alignof(void*), "Objects should always be at least pointer-aligned.");
 static const size_t maximumExtraSpaceForAlignment = minimumObjectAlignment - alignof(void*);