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Re: [Qemu-devel] [PATCH 0/9] valgrind/i386/s390x: memcheck false positiv
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 0/9] valgrind/i386/s390x: memcheck false positives |
Date: |
Mon, 03 Nov 2014 13:27:53 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
On 30/10/2014 14:20, Christian Borntraeger wrote:
> Am 30.10.2014 14:03, schrieb Paolo Bonzini:
>> On 10/30/2014 10:36 AM, Christian Borntraeger wrote:
>>> Some of these things could
>>> also be fixed in valgrind, but it will take a while until these changes
>>> hit a release or distros.
>>
>> Ok, it's sensible to have it fixed in QEMU if it's temporary. Which
>> could not be fixed in valgrind?
>
> This is a tricky question. A typical annotation in valgrind for an more
> complex ioctl looks like
>
> case VKI_SIOCGMIIREG: /* get hardware entry registers */
> PRE_MEM_RASCIIZ( "ioctl(SIOCGIFMIIREG)",
> (Addr)((struct vki_ifreq *)ARG3)->vki_ifr_name );
> PRE_MEM_READ( "ioctl(SIOCGIFMIIREG)",
> (Addr)&((struct vki_mii_ioctl_data *)&((struct vki_ifreq
> *)ARG3)->vki_ifr_data)->phy_id,
> sizeof(((struct vki_mii_ioctl_data *)&((struct vki_ifreq
> *)ARG3)->vki_ifr_data)->phy_id) );
> PRE_MEM_READ( "ioctl(SIOCGIFMIIREG)",
> (Addr)&((struct vki_mii_ioctl_data *)&((struct vki_ifreq
> *)ARG3)->vki_ifr_data)->reg_num,
> sizeof(((struct vki_mii_ioctl_data *)&((struct vki_ifreq
> *)ARG3)->vki_ifr_data)->reg_num) );
> PRE_MEM_WRITE( "ioctl(SIOCGIFMIIREG)", ARG3,
> sizeof(struct vki_ifreq));
> break;
>
> This scheme works fine as long as the ioctl is unchanged.
> So any ioctl that has padding and no flags this should be doable.
>
> For all KVM ioctls with reserved fields that might become used on certain
> flags, we have two options:
>
> a: we would instruct valgrind to not check the reserved fields
> Whenever we start using them, we would still not check those field
>
> b: we would instruct valgrind to not check the reserved fields if flags has a
> certain value (e.g. 0), otherwise all reserved fields would be checked.
> Whenever we start using the reserved fields, valgrind would complain unless
> we write all. So in that case we have to modify valgrind again
>
> In essence a will cause false negatives, b will cause false positives
>
> I think b is preferred
I agree.
Paolo
- Re: [Qemu-devel] [PATCH 0/9] valgrind/i386/s390x: memcheck false positives,
Paolo Bonzini <=