Re: [libvirt] [PATCH 11/11] hypervisor: Revisit Coverity issues regarding cpumap
On 01/30/2013 11:51 AM, John Ferlan wrote:
Turns out the issue regarding ptr_arith and sign_exension weren't
false
positives. When shifting an 'unsigned char' as a target, it gets promoted
to an 'int'; however, that 'int' cannot be shifted 32 bits which was how
the algorithm was written. For the ptr_arith rather than index into the
cpumap, change the to address as necessary and assign directly.
---
src/xen/xen_hypervisor.c | 10 +++++-----
for (j = 0; j < maplen; j++) {
- /* coverity[ptr_arith] */
- /* coverity[sign_extension] */
- *(pm + (j / 8)) |= cpumap[j] << (8 * (j & 7));
+ if ((j & 7) == 0)
+ pm = (uint64_t *)((uint64_t)&xen_cpumap + (j & ~0x7UL));
I'm not happy with how this turned out. We are turning an address into
a pointer but not via intptr_t (probably warnings on mingw); then doing
math on that pointer, then turning the result back into a uint64_t
pointer. It looks like we are risking alignment errors.
+ *pm |= (uint64_t)cpumap[j] << (8 * (j & 7));
This part looks better, although I can see why you had to push a
followup to silence a false negative compiler warning about pm
potentially being used uninitialized.
I still think we can do a better job; the whole goal of this code is to
write an endian-specific ordering of a multiple of 8 bytes; I can't help
but wonder if my concurrent work on a new virendian.h header would be a
nicer-looking solution here.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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