linux-kernel - RE: [PATCH mm] kfence: fix printk format for ptrdiff

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Date:   Wed, 17 Mar 2021 12:51:58 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christophe Leroy' <christophe.leroy@...roup.eu>,
        Segher Boessenkool <segher@...nel.crashing.org>
CC:     Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Linux Memory Management List" <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: RE: [PATCH mm] kfence: fix printk format for ptrdiff_t

From: Christophe Leroy
> Sent: 16 March 2021 15:41
...
> >> include/linux/types.h:typedef __kernel_ptrdiff_t	ptrdiff_t;
> >>
> >> And get:
> >>
> >>    CC      mm/kfence/report.o
> >> In file included from ./include/linux/printk.h:7,
> >>                   from ./include/linux/kernel.h:16,
> >>                   from mm/kfence/report.c:10:
> >> mm/kfence/report.c: In function 'kfence_report_error':
> >> ./include/linux/kern_levels.h:5:18: warning: format '%td' expects argument
> >> of type 'ptrdiff_t', but argument 6 has type 'long int' [-Wformat=]
> >
> > This is declared as
> >          const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
> > so maybe something with that goes wrong?  What happens if you delete the
> > (useless) "const" here?

The obvious thing to try is changing it to 'int'.
That will break 64bit builds, but if it fixes the 32bit one
it will tell you what type gcc is expecting.

	David

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