[Webkit-unassigned] [Bug 198518] REGRESSION(r245586): static assertion failed: Match result and EncodedMatchResult should be the same size

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=198518

--- Comment #11 from Keith Miller <keith_miller at apple.com> ---
(In reply to Mark Lam from comment #10)
> Comment on attachment 372782 [details]
> proposed patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=372782&action=review
> 
> Also missing ChangeLog.
> 
> > Source/JavaScriptCore/runtime/MatchResult.h      2019-06-24 18:36:36.947345256 +0000:43
> >  #if CPU(ARM64) || CPU(X86_64)
> > +#define ENCODEDMATCHRESULT_IS_MATCHRESULT 1
> >  using EncodedMatchResult = MatchResult;
> > -#else
> > +#elif (defined(SIZE_WIDTH) && (SIZE_WIDTH == 32)) || (SIZE_MAX == 0xffffffff)
> > +#define ENCODEDMATCHRESULT_IS_MATCHRESULT 0
> >  using EncodedMatchResult = uint64_t;
> > +#else
> > +#define ENCODEDMATCHRESULT_IS_MATCHRESULT 1
> > +using EncodedMatchResult = MatchResult;
> >  #endif
> 
> This fix is invalid.
> 
> The issue is that MatchResult contains 2 size_t values.  This means, on
> 32-bit platforms, sizeof(MatchResult) is 64-bit, but on 64-bit platforms,
> sizeof(MatchResult) is 128-bit.
> 
> The proper fix is simply:
> 
> #if CPU(ADDRESS32)
> using EncodedMatchResult = uint64_t;
> static_assert(sizeof(size_t) == sizeof(uint32_t), "");
> #else
> using EncodedMatchResult = MatchResult;
> #endif

I think a better assertion would be static_assert(sizeof(EncodedMatchResult) == 2 * sizeof(size_t)), which should be true on all platforms. I like the rest of your change though.

The point of the EncodedMatchResult type is to ensure that the C calling convention will return the result in the two return registers rather than on the stack.

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