Bug 196959 – DOMMatrixReadOnly and WebKitCSSMatrix should have padding to make TransformationMatrix 16byte aligned

• Status: NEW
• Component: DOM

[Yusuke Suzuki]

This issue is found in IsoHeap extension patch[1].

[1]: https://bugs.webkit.org/show_bug.cgi?id=196837

[Yusuke Suzuki]

Related to IsoHeap.

[Yusuke Suzuki]

Created attachment 367505 [details]
Patch

[Yusuke Suzuki]

Created attachment 367506 [details]
Patch

[Yusuke Suzuki]

Comment on attachment 367506 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=367506&action=review

> Source/WebCore/css/DOMMatrixReadOnly.h:152
> +    std::aligned_storage<sizeof(TransformationMatrix), 8>::type m_storage;

aligned_storage just adds alignment information, not adding appropriate padding. So we need to have a padding manually.
https://en.cppreference.com/w/cpp/types/aligned_storage
Typical aligned_storage implementation.
```
template<std::size_t Len, std::size_t Align /* default alignment not implemented */>
struct aligned_storage {
    struct type {
        alignas(Align) unsigned char data[Len];
    };
};
```

[Yusuke Suzuki]

Let's extract this storage part as PaddedAlignedStorage.

[Yusuke Suzuki]

Created attachment 367512 [details]
Patch

[Yusuke Suzuki]

Created attachment 367513 [details]
Patch

[Yusuke Suzuki]

The patch becomes not so much related to bmalloc. Remove bmalloc keyword.

[Yusuke Suzuki]

Created attachment 367514 [details]
Patch

[Yusuke Suzuki]

Comment on attachment 367514 [details]
Patch

Still considering

[EWS Watchlist]

Comment on attachment 367514 [details]
Patch

Attachment 367514 [details] did not pass win-ews (win):
Output: https://webkit-queues.webkit.org/results/11885059

New failing tests:
js/dom/custom-constructors.html

[EWS Watchlist]

Created attachment 367532 [details]
Archive of layout-test-results from ews202 for win-future

The attached test failures were seen while running run-webkit-tests on the win-ews.
Bot: ews202  Port: win-future  Platform: CYGWIN_NT-6.1-2.10.0-0.325-5-3-x86_64-64bit

[Ahmad Saleem]

This patch was adding new WTF - PaddedAlignedStorage.h

Also modifying this, which is not modified:

https://github.com/WebKit/WebKit/blob/64f843f962fd4b62b95fb3c3c53127b6f526fbcd/Source/WTF/wtf/StdLibExtras.h#L89

https://github.com/WebKit/WebKit/blob/64f843f962fd4b62b95fb3c3c53127b6f526fbcd/Source/WTF/wtf/StdLibExtras.h#L107

In DOMMatrix.cpp, it is still referring old (some examples below):

https://github.com/WebKit/WebKit/blob/edb309e77f7aa09b0799c4508214dbbf75ae0117/Source/WebCore/css/DOMMatrix.cpp#L142

https://github.com/WebKit/WebKit/blob/edb309e77f7aa09b0799c4508214dbbf75ae0117/Source/WebCore/css/DOMMatrix.cpp#L129

https://github.com/WebKit/WebKit/blob/edb309e77f7aa09b0799c4508214dbbf75ae0117/Source/WebCore/css/DOMMatrix.cpp#L151

_________

[e-mail] - These above are just few examples, is this needed anymore? Thanks!