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From: Peter Maydell <peter.maydell@linaro.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
	John Snow <jsnow@redhat.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Michael Roth <mdroth@linux.vnet.ibm.com>
Subject: Re: [Qemu-devel] clang -fsanitize=undefined warnings in the string visitors
Date: Thu, 14 Jan 2016 12:52:51 +0000	[thread overview]
Message-ID: <CAFEAcA8Ac8R_+egy9opa-JfLtSh7ohmJ+gQRbx49UbiHa09tFA@mail.gmail.com> (raw)
In-Reply-To: <56979831.6070204@redhat.com>

On 14 January 2016 at 12:44, Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 14/01/2016 12:15, Peter Maydell wrote:
>> Not that I saw -- ping again, Paolo. This is the only warning
>> that clang's sanitizer currently produces for me, and arithmetic
>> overflows on addition seem genuinely worth investigation...
>
> It happens when the range is 2^64 in size.
>
> Does it still matter if we've decided to use -fwrapv because of left
> shifts?  Or are we still considering the possibility to use -std=gnu89
> (where left shifts give unspecified behavior rather than undefined)?

I think we agreed that we wanted signed shift behaviour if we
could get it, but this is all addition. The code looks a bit
odd to me anyway -- the Range type specifies ranges within a
64-bit address space and thus an unsigned start and end point,
but the code in string-output-visitor.c is specifically using
and feeding in signed values for the start and end.

thanks
-- PMM

  reply	other threads:[~2016-01-14 12:53 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-23 23:17 [Qemu-devel] clang -fsanitize=undefined warnings in the string visitors Peter Maydell
2015-02-05 17:03 ` Peter Maydell
2015-05-11  8:53   ` Peter Maydell
2015-05-11  9:07     ` Paolo Bonzini
2015-05-29 10:56       ` Peter Maydell
2015-05-29 11:12         ` Paolo Bonzini
2015-10-01 10:47           ` Peter Maydell
2015-10-01 13:38             ` Paolo Bonzini
2015-11-05 20:05               ` John Snow
2016-01-14 11:15                 ` Peter Maydell
2016-01-14 12:44                   ` Paolo Bonzini
2016-01-14 12:52                     ` Peter Maydell [this message]
2015-10-01 14:58             ` Eric Blake

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