On 04/26/2012 12:56 AM, Laine Stump wrote: > The ATTRIBUTE_NONNULL(m) macro normally resolves to the gcc builtin > __attribute__((__nonnull__(m))). The effect of this in gcc is > unfortunately only to make gcc believe that "m" can never possibly be > NULL, *not* to add in any checks to guarantee that it isn't ever NULL > (i.e. it is an optimization aid, *not* something to verify code > correctness.) - see the following gcc bug report for more details: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17308 > > Static source analyzers such as clang and coverity apparently can use > ATTRIBUTE_NONNULL(), though, to detect dead code (in the case that the > arg really is guaranteed non-NULL), as well as situations where an > obviously NULL arg is given to the function. > > https://bugzilla.redhat.com/show_bug.cgi?id=815270 is a good example > of a bug caused by erroneous application of ATTRIBUTE_NONNULL(). > Several people spent a long time staring at this code and not finding > the problem, because the problem wasn't in the function itself, but in > the prototype that specified ATTRIBUTE_NONNULL() for an arg that > actually *wasn't* always non-NULL, and caused a segv when dereferenced > (even though the code that dereferenced the pointer was inside an if() > that checked for a NULL pointer, that code was optimized out by gcc). > > There may be some very small gain to be had from the optimizations > that can be inferred from ATTRIBUTE_NONNULL(), but it seems safer to > err on the side of generating code that behaves as expected, while > turning on the attribute for static analyzers. > > (dissenting opinions welcome :-)
None from me :) > --- > src/internal.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/src/internal.h b/src/internal.h > index ef81cda..83f468d 100644 > --- a/src/internal.h > +++ b/src/internal.h > @@ -182,7 +182,7 @@ > # endif > > # ifndef ATTRIBUTE_NONNULL > -# if __GNUC_PREREQ (3, 3) > +# if __GNUC_PREREQ (3, 3) && STATIC_ANALYSIS > # define ATTRIBUTE_NONNULL(m) __attribute__((__nonnull__(m))) ACK. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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