[Webkit-unassigned] [Bug 147393] Parse the entire WebAssembly modules

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=147393

--- Comment #13 from Sukolsak Sakshuwong <sukolsak at gmail.com> ---
Thanks.

(In reply to comment #10)
> 1. Use a do-while loop because it is more succinct and easier to read.

Done.

> 2. Use a uint64_t local value instead of storing into the result directly.
> Using the local allows the compiler to put it in a register, and register
> operations are cheap.  We only incur the memory write to result at the end.

Used a local value.

> 3. When the computation is done,
>     (1) break out of the loop,
>     (2) validate that the computed value is within size of a uint32,  and
>     (3) copy the local value into the result.  
> 
> 4. The loop can loop while (value < numeric_limits<uint32_t>::max()).  This
> ensures that we don't overflow our uint64_t local value and that the
> validation check in 3.2 will work as expected.

As discussed on IRC, checking that (value < numeric_limits<uint32_t>::max()) is not enough, because the bytes could be 0x80 0x80 0x80 0x80 0x80 ... . Checking that the number of bytes doesn't exceed 5 and that the fifth byte is <= 0b00001111 should prevent that and also eliminate the need for uint64_t.

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