ARMv8, GCC 4.9 and necessary code optimized away?
Wed Jun 1 07:32:00 GMT 2016
On 31/05/16 21:37, Jeffrey Walton wrote:
>> Like Florian said, 'w' is not being used so the compiler may optimise the
>> whole sequence away.
> I'm pretty sure this is another instance of a language defect. The
> C/C++ language does not allow us to properly express ourselves, and
> the result is the removal of critical code.
The problem here is that GCC knows that the CRC instructions have
no side effects beyond their operands. So GCC doesn't generate
> This is at least the third or fourth time. The one prior to this
> resulted in CVE-2016-3995.
Of course GCC deletes dead code. That's one of the most basic
In your case I'd just use the result as an input operand into an
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