[Mesa-dev] [PATCH] list: add some iterator debug

[Rob Clark]

On Sat, May 25, 2019 at 11:13 AM Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>
> On Sat, May 25, 2019 at 2:03 PM Rob Clark <robdclark at gmail.com> wrote:
> >
> > From: Rob Clark <robdclark at chromium.org>
> >
> > Debugging use of unsafe iterators when you should have used the _safe
> > version sucks.  Add some DEBUG build support to catch and assert if
> > someone does that.
> >
> > I didn't update the UPPERCASE verions of the iterators.  They should
> > probably be deprecated/removed.
> >
> > Signed-off-by: Rob Clark <robdclark at chromium.org>
> > ---
> >  src/util/list.h | 23 ++++++++++++++++++-----
> >  1 file changed, 18 insertions(+), 5 deletions(-)
> >
> > diff --git a/src/util/list.h b/src/util/list.h
> > index 09d1b4cae64..6d89a42b226 100644
> > --- a/src/util/list.h
> > +++ b/src/util/list.h
> > @@ -43,6 +43,13 @@
> >  #include <assert.h>
> >  #include "c99_compat.h"
> >
> > +#ifdef DEBUG
> > +#  define LIST_DEBUG 1
> > +#else
> > +#  define LIST_DEBUG 0
> > +#endif
> > +
> > +#define list_assert(cond, msg)  ({ if (LIST_DEBUG) assert((cond) && msg); })
>
> Not sure if it's worth worrying about, but this style of macro
> definition can be dangerous. One might use it as
>
> if (x) list_assert()
> else blah;
>
> With the macro defined as-is, the "else blah" will get attached to the
> if in the macro. I believe the common style is to do do {}while(0) to
> avoid such issues (or to use an inline function). Alternatively, just
> define it differently for LIST_DEBUG vs not.
>

I think the ({ ... }) should save the day..

(hmm, is that c99 or a gnu thing?  I've it isn't avail on some
compilers I guess we should disable list_assert() for those?)

BR,
-R