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([2620:15c:211:201:349c:3078:d005:5a7e]) by smtp.gmail.com with ESMTPSA id b8-20020a17090a5a0800b001f56315f9efsm3829796pjd.32.2022.08.25.10.39.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Aug 2022 10:39:04 -0700 (PDT) Message-ID: <7bc72b9d-79b0-5b8c-18c4-4a5c914efdc5@acm.org> Date: Thu, 25 Aug 2022 10:39:02 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 From: Bart Van Assche Subject: Re: [for-linus][PATCH 01/10] tracing: Suppress sparse warnings triggered by is_signed_type() To: Linus Torvalds Cc: Rasmus Villemoes , Steven Rostedt , linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Christoph Hellwig , Luc Van Oostenryck , Jens Axboe , Kees Cook References: <20220821000737.328590235@goodmis.org> <20220821000844.510643400@goodmis.org> <5700ac75-f6a9-877e-4011-9b314f12b5ab@acm.org> <02daa3d6-2847-d7e0-e23e-411076c6d4db@rasmusvillemoes.dk> <0163b361-14bf-7b4c-751a-14f1a004b1a9@acm.org> <353e5bbd-cdd1-f818-6a2f-9a7c800f9879@acm.org> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 and a second definition in . As suggested by Linus Torvalds, move the definition of the is_signed_type() macro into the 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 Cc: Steven Rostedt Cc: Kees Cook Signed-off-by: Bart Van Assche --- include/linux/compiler.h | 6 ++++++ include/linux/overflow.h | 1 - include/linux/trace_events.h | 2 -- 3 files changed, 6 insertions(+), 3 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 01ce94b58b42..7713d7bcdaea 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -239,6 +239,12 @@ static inline void *offset_to_ptr(const int *off) /* &a[0] degrades to a pointer: a different type from an array */ #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0])) +/* + * Whether 'type' is a signed type or an unsigned type. Supports scalar types, + * bool and also pointer types. + */ +#define is_signed_type(type) (((type)(-1)) < (__force type)1) + /* * This is needed in functions which generate the stack canary, see * arch/x86/kernel/smpboot.c::start_secondary() for an example. diff --git a/include/linux/overflow.h b/include/linux/overflow.h index f1221d11f8e5..0eb3b192f07a 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -30,7 +30,6 @@ * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html - * credit to Christian Biere. */ -#define is_signed_type(type) (((type)(-1)) < (type)1) #define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type))) #define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T))) #define type_min(T) ((T)((T)-type_max(T)-(T)1)) diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index b18759a673c6..8401dec93c15 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -814,8 +814,6 @@ extern int trace_add_event_call(struct trace_event_call *call); extern int trace_remove_event_call(struct trace_event_call *call); extern int trace_event_get_offsets(struct trace_event_call *call); -#define is_signed_type(type) (((type)(-1)) < (type)1) - int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set); int trace_set_clr_event(const char *system, const char *event, int set); int trace_array_set_clr_event(struct trace_array *tr, const char *system,