Messages in this thread | | | Date | Thu, 25 Aug 2022 11:17:49 -0700 | From | Kees Cook <> | Subject | Re: [for-linus][PATCH 01/10] tracing: Suppress sparse warnings triggered by is_signed_type() |
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On Thu, Aug 25, 2022 at 10:39:02AM -0700, Bart Van Assche wrote: > On 8/24/22 17:40, Linus Torvalds wrote: > > Actually, thinking about it, that was simple enough. > > > > -#define is_signed_type(type) (((type)(-1)) < (type)1) > > +#define is_signed_type(type) (((type)(-1)) < (__force type)1) > > > > should work. > > > > It looks a bit odd, because we only force one side. > > > > But we only need to force one side, because the '-1' doesn't have any > > issues with bitwise types, the same way 0 doesn't. > > > > So only '1' needs to be force-cast to avoid a warning about casting an > > integer to a bitwise type. > > > > And since that -1 counts as an unrestricted value after a cast, now > > the ordered comparison doesn't warn either. > > > > Now, admittedly I think sparse should also allow a forced cast of an > > unrestricted value to be unrestricted, so I think I should do this > > > > static int restricted_value(struct expression *v, struct symbol *type) > > { > > - if (v->type == EXPR_CAST) > > + if (v->type == EXPR_CAST || v->type = EXPR_FORCE_CAST) > > v = v->cast_expression; > > > > in sparse, but even without that the above "is_signed_type()" macro > > should make sparse happy (with that current tree of mine). > > > > And since we don't now need to cast 0, gcc won't complain about that > > NULL pointer comparison. > > > > Does that solve things for you? > > Yes, thank you! No sparse warnings are triggered by the is_signed_type() > macro and the gcc warning about ordered comparison of a pointer with the > null pointer is gone. > > The patch I came up with is available below. If nobody picks it up from > this email I will try to find an appropriate kernel maintainer to send > this kernel patch to. > > Thanks, > > Bart. > > > From: Bart Van Assche <bvanassche@acm.org> > Date: Tue, 23 Aug 2022 12:59:25 -0700 > Subject: [PATCH] tracing: Define the is_signed_type() macro once > > There are two definitions of the is_signed_type() macro: one in > <linux/overflow.h> and a second definition in <linux/trace_events.h>. > > As suggested by Linus Torvalds, move the definition of the > is_signed_type() macro into the <linux/compiler.h> header file. Change > the definition of the is_signed_type() macro to make sure that it does > not trigger any sparse warnings with future versions of sparse for > bitwise types. See also: > https://lore.kernel.org/all/CAHk-=whjH6p+qzwUdx5SOVVHjS3WvzJQr6mDUwhEyTf6pJWzaQ@mail.gmail.com/ > https://lore.kernel.org/all/CAHk-=wjQGnVfb4jehFR0XyZikdQvCZouE96xR_nnf5kqaM5qqQ@mail.gmail.com/ > > Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Kees Cook <keescook@chromium.org> > Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Looks good to me; thanks!
Acked-by: Kees Cook <keescook@chromium.org>
-- Kees Cook
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