On 04/26/2012 04:46 AM, Eric Blake wrote:
Eric, I ran Coverity on current commit 'f78024b util: fix crash when starting macvtap interfaces',On 04/25/2012 02:01 PM, Laine Stump wrote:This patch resolves https://bugzilla.redhat.com/show_bug.cgi?id=815270 The function virNetDevMacVLanVPortProfileRegisterCallback() takes an arg "virtPortProfile", and was checking it for non-NULL before using it. However, the prototype for virNetDevMacVLanPortProfileRegisterCallback had marked that arg with ATTRIBUTE_NONNULL(). Contrary to what one may think, ATTRIBUTE_NONNULL() does not provide any guarantee that an arg marked as such really is always non-null; the only effect to the code generated by gcc, is that gcc *assumes* it is non-NULL; this results in, for example, the check for a non-NULL value being optimized out. (Unfortunately, this code removal only occurs when optimization is enabled, and I am in the habit of doing local builds with optimization off to ease debugging, so the bug didn't show up in my earlier local testing). In general, virPortProfile might always be NULL, so it shouldn't be marked as ATTRIBUTE_NONNULL. One other function prototype made this same error, so this patch fixes it as well.Might be worth linking to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17308--- src/util/virnetdevmacvlan.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)ACK. What an insidious bug. As Laine and I discussed on IRC, I'm half wondering if we should just do: #ifdef STATIC_ANALYSIS && /* attributes supported */ # define ATTRIBUTE_NONNULL(n) __attribute__((__nonnull__(n))) #else # define ATTRIBUTE_NONNULL(n) /* empty, due to gcc lameness */ #endif so that our code will be pessimized under normal compiles, but _at least_ places where we have bugs with improper use of the attribute won't cause gcc to miscompile things; but still let us get NULL checking when running clang or Coverity. I also wonder if this has been detected by Coverity (checking a nonnull parameter for NULL is dead code, which Coverity does tend to flag), and we just haven't been following Coverity closely enough to notice.
Coverity hasn't complain this issue, although I also enabled '--security' checkers in Coverity.
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