From: Mathieu Malaterre <malat@debian.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Christophe LEROY <christophe.leroy@c-s.fr>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Paul Mackerras <paulus@samba.org>,
LKML <linux-kernel@vger.kernel.org>, Jiri Slaby <jslaby@suse.com>
Subject: Re: [PATCH 05/21] powerpc: Avoid comparison of unsigned long >= 0 in pfn_valid
Date: Fri, 2 Mar 2018 20:54:27 +0100 [thread overview]
Message-ID: <CA+7wUsz7srOXwehLjuSn_SEgCUkGxu9bq6aOw5AeOaiiipBNtg@mail.gmail.com> (raw)
In-Reply-To: <20180226084602.GR21977@gate.crashing.org>
On Mon, Feb 26, 2018 at 9:46 AM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> On Mon, Feb 26, 2018 at 07:32:03AM +0100, Christophe LEROY wrote:
>> Le 25/02/2018 à 18:22, Mathieu Malaterre a écrit :
>> >-#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) <
>> >max_mapnr)
>> >+#define pfn_valid(pfn) \
>> >+ (((pfn) - ARCH_PFN_OFFSET) < (max_mapnr - ARCH_PFN_OFFSET))
>>
>> What will happen when ARCH_PFN_OFFSET is not nul and pfn is lower than
>> ARCH_PFN_OFFSET ?
>
> It will work fine.
>
> Say you are asking for a <= x < b so (in actual integers, no overflow)
> that is 0 <= x-a < b-a and you also assume x-a overflows, so that we
> are actually comparing x-a+M < b-a with M = 2**32 or such (the maximum
> value in the unsigned integer type plus one). This comparison is
> obviously always false.
>
> (It also works if b < a btw).
>
>
Thanks Segher !
Christophe does that clarify things or do you want me to update the
commit message ?
WARNING: multiple messages have this Message-ID (diff)
From: Mathieu Malaterre <malat@debian.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Christophe LEROY <christophe.leroy@c-s.fr>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Paul Mackerras <paulus@samba.org>,
LKML <linux-kernel@vger.kernel.org>, Jiri Slaby <jslaby@suse.com>
Subject: Re: [PATCH 05/21] powerpc: Avoid comparison of unsigned long >= 0 in pfn_valid
Date: Fri, 2 Mar 2018 20:54:27 +0100 [thread overview]
Message-ID: <CA+7wUsz7srOXwehLjuSn_SEgCUkGxu9bq6aOw5AeOaiiipBNtg@mail.gmail.com> (raw)
In-Reply-To: <20180226084602.GR21977@gate.crashing.org>
On Mon, Feb 26, 2018 at 9:46 AM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> On Mon, Feb 26, 2018 at 07:32:03AM +0100, Christophe LEROY wrote:
>> Le 25/02/2018 =C3=A0 18:22, Mathieu Malaterre a =C3=A9crit :
>> >-#define pfn_valid(pfn) ((pfn) >=3D ARCH_PFN_OFFSET && (pf=
n) <
>> >max_mapnr)
>> >+#define pfn_valid(pfn) \
>> >+ (((pfn) - ARCH_PFN_OFFSET) < (max_mapnr - ARCH_PFN_OFFSET)=
)
>>
>> What will happen when ARCH_PFN_OFFSET is not nul and pfn is lower than
>> ARCH_PFN_OFFSET ?
>
> It will work fine.
>
> Say you are asking for a <=3D x < b so (in actual integers, no overflow=
)
> that is 0 <=3D x-a < b-a and you also assume x-a overflows, so that we
> are actually comparing x-a+M < b-a with M =3D 2**32 or such (the maximu=
m
> value in the unsigned integer type plus one). This comparison is
> obviously always false.
>
> (It also works if b < a btw).
>
>
Thanks Segher !
Christophe does that clarify things or do you want me to update the
commit message ?
next prev parent reply other threads:[~2018-03-02 19:54 UTC|newest]
Thread overview: 103+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-25 17:22 [PATCH 00/21] powerpc/gamecube: make W=1 compilation errors free Mathieu Malaterre
2018-02-25 17:22 ` [PATCH 01/21] powerpc: Remove warning on array size when empty Mathieu Malaterre
2018-02-25 18:53 ` Segher Boessenkool
2018-02-26 14:44 ` Andy Shevchenko
2018-02-26 14:44 ` Andy Shevchenko
2018-02-26 14:45 ` Andy Shevchenko
2018-02-27 7:25 ` Mathieu Malaterre
2018-02-27 7:33 ` Christophe LEROY
2018-02-27 7:44 ` Mathieu Malaterre
2018-02-27 7:44 ` Mathieu Malaterre
2018-02-27 15:52 ` Andy Shevchenko
2018-02-27 17:25 ` Mathieu Malaterre
2018-02-27 17:25 ` Mathieu Malaterre
2018-02-27 20:42 ` Segher Boessenkool
2018-02-28 15:50 ` Andy Shevchenko
2018-03-01 2:55 ` Michael Ellerman
2018-03-01 2:55 ` Michael Ellerman
2018-03-01 7:01 ` Mathieu Malaterre
2018-03-01 7:01 ` Mathieu Malaterre
2018-03-01 9:33 ` Michael Ellerman
2018-03-01 9:33 ` Michael Ellerman
2018-03-02 19:49 ` [PATCH v2 " Mathieu Malaterre
2018-03-14 9:28 ` [v2,01/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 02/21] powerpc: Move the inline keyword at the beginning of function declaration Mathieu Malaterre
2018-03-14 9:27 ` [02/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 03/21] powerpc: Mark the variable earlycon_acpi_spcr_enable maybe_unused Mathieu Malaterre
2018-03-04 10:54 ` Michael Ellerman
2018-03-04 10:54 ` Michael Ellerman
2018-03-10 18:08 ` Mathieu Malaterre
2018-03-10 18:08 ` Mathieu Malaterre
2018-02-25 17:22 ` [PATCH 04/21] powerpc: Mark both tmp variables as unused Mathieu Malaterre
2018-03-14 9:27 ` [04/21] " Michael Ellerman
2018-03-14 10:38 ` [PATCH 04/21] " Christophe LEROY
2018-03-16 14:08 ` Michael Ellerman
2018-03-16 14:08 ` Michael Ellerman
2018-02-25 17:22 ` [PATCH 05/21] powerpc: Avoid comparison of unsigned long >= 0 in pfn_valid Mathieu Malaterre
2018-02-26 6:32 ` Christophe LEROY
2018-02-26 7:49 ` Mathieu Malaterre
2018-02-26 7:49 ` Mathieu Malaterre
2018-02-26 8:46 ` Segher Boessenkool
2018-03-02 19:54 ` Mathieu Malaterre [this message]
2018-03-02 19:54 ` Mathieu Malaterre
2018-03-03 7:45 ` christophe leroy
2018-03-04 10:55 ` Michael Ellerman
2018-03-04 10:55 ` Michael Ellerman
2018-03-04 19:46 ` christophe leroy
2018-03-07 20:34 ` [PATCH v2 " Mathieu Malaterre
2018-03-14 9:28 ` [v2, " Michael Ellerman
2018-02-25 17:22 ` [PATCH 06/21] powerpc: Avoid comparison of unsigned long >= 0 in __access_ok Mathieu Malaterre
2018-02-26 6:34 ` Christophe LEROY
2018-02-26 6:50 ` Christophe LEROY
2018-02-26 7:44 ` Mathieu Malaterre
2018-02-26 7:44 ` Mathieu Malaterre
2018-02-26 17:50 ` Mathieu Malaterre
2018-02-26 17:50 ` Mathieu Malaterre
2018-02-26 20:00 ` christophe leroy
2018-02-26 22:17 ` Segher Boessenkool
2018-03-02 19:50 ` [PATCH v2 " Mathieu Malaterre
2018-03-03 7:44 ` christophe leroy
2018-03-14 9:28 ` [v2, " Michael Ellerman
2018-02-25 17:22 ` [PATCH 07/21] powerpc: Make functions flipper_pic_init & ug_udbg_putc static Mathieu Malaterre
2018-03-14 9:27 ` [07/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 08/21] powerpc: Make function __giveup_fpu static Mathieu Malaterre
2018-03-14 9:28 ` [08/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 09/21] powerpc: Make function save_all static Mathieu Malaterre
2018-02-25 17:22 ` [PATCH 10/21] powerpc: Add missing prototype for slb_miss_bad_addr Mathieu Malaterre
2018-03-14 9:27 ` [10/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 11/21] powerpc: Add missing prototype for hdec_interrupt Mathieu Malaterre
2018-03-14 9:27 ` [11/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 12/21] powerpc: Add missing prototype for time_init Mathieu Malaterre
2018-03-14 9:27 ` [12/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 13/21] powerpc: Add missing prototype for arch_dup_task_struct Mathieu Malaterre
2018-03-14 9:27 ` [13/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 14/21] powerpc: Add missing prototype for arch_irq_work_raise Mathieu Malaterre
2018-03-14 9:27 ` [14/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 15/21] powerpc: Add missing prototype for MMU_setup Mathieu Malaterre
2018-03-04 10:54 ` Michael Ellerman
2018-03-04 10:54 ` Michael Ellerman
2018-03-07 20:32 ` [PATCH v2 15/21] powerpc: Make function MMU_setup static Mathieu Malaterre
2018-03-14 9:28 ` [v2,15/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 16/21] powerpc: Add missing prototype for init_IRQ Mathieu Malaterre
2018-03-14 9:28 ` [16/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 17/21] powerpc: Add missing prototype for sys_debug_setcontext Mathieu Malaterre
2018-03-04 10:54 ` Michael Ellerman
2018-03-04 10:54 ` Michael Ellerman
2018-03-07 20:37 ` Mathieu Malaterre
2018-03-07 20:37 ` Mathieu Malaterre
2018-03-08 10:36 ` Michael Ellerman
2018-03-08 10:36 ` Michael Ellerman
2018-03-26 18:56 ` Mathieu Malaterre
2018-03-26 18:56 ` Mathieu Malaterre
2018-03-27 8:50 ` Michael Ellerman
2018-03-27 8:50 ` Michael Ellerman
2018-03-14 9:28 ` [17/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 18/21] powerpc: Add missing prototypes for sys_sigreturn & sys_rt_sigreturn Mathieu Malaterre
2018-03-14 9:28 ` [18/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 19/21] powerpc: Add missing prototypes for hw_breakpoint_handler & arch_unregister_hw_breakpoint Mathieu Malaterre
2018-03-14 9:28 ` [19/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 20/21] powerpc: Add missing prototypes for ppc_select & ppc_fadvise64_64 Mathieu Malaterre
2018-03-14 9:28 ` [20/21] " Michael Ellerman
2018-02-25 17:22 ` [PATCH 21/21] powerpc: Add missing prototypes in setup_32.c Mathieu Malaterre
2018-03-08 11:44 ` Michael Ellerman
2018-03-14 9:28 ` [21/21] " Michael Ellerman
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