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

[Ilia Mirkin]

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.

Cheers,

  -ilia