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
