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Re: [Qemu-ppc] [PULL 00/40] ppc patch queue 2015-06-03

From: Paolo Bonzini
Subject: Re: [Qemu-ppc] [PULL 00/40] ppc patch queue 2015-06-03
Date: Fri, 05 Jun 2015 17:20:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/06/2015 17:08, Peter Maydell wrote:
>> > Can someone add a checkpatch rule that forbids shifting left U or UL
>> > constants (i.e. only ULL)?  That would alleviate my concerns with these
>> > ubsan warnings.
> ...but things like "(1U << 31)" are entirely valid.

They're only valid until someone does a ~ on them.  I think it's
reasonable to forbid them in our coding standards, if we want to fix
ubsan's warning of (1 << 31).

I don't think it's reasonable for compiler writers to exploit the
undefinedness of (1 << 31) anyway, and if it were possible to shut up
ubsan about this particular kind of undefined behavior, I would prefer it.


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