From: Segher Boessenkool <segher@kernel.crashing.org>
To: Kees Cook <keescook@chromium.org>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
Michael Ellerman <mpe@ellerman.id.au>,
Jinbum Park <jinb.park7@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only"
Date: Mon, 25 Sep 2017 02:37:21 -0500 [thread overview]
Message-ID: <20170925073721.GM8421@gate.crashing.org> (raw)
In-Reply-To: <CAGXu5jJ54+bCcXaPK1ExsxtTDPHNn1+1gywb3TDbe-SEtt1zuQ@mail.gmail.com>
On Sun, Sep 24, 2017 at 12:17:51PM -0700, Kees Cook wrote:
> On Thu, Sep 21, 2017 at 2:37 AM, Christophe Leroy
> <christophe.leroy@c-s.fr> wrote:
> > On powerpc, RODATA_TEST fails with message the following messages:
> >
> > [ 6.199505] Freeing unused kernel memory: 528K
> > [ 6.203935] rodata_test: test data was not read only
> >
> > This is because GCC allocates it to .data section:
> >
> > c0695034 g O .data 00000004 rodata_test_data
>
> Uuuh... that seems like a compiler bug. It's marked "const" -- it
> should never end up in .data. I would argue that this has done exactly
> what it was supposed to do, and shows that something has gone wrong.
> It should always be const. Adding "static" should just change
> visibility. (I'm not opposed to the static change, but it seems to
> paper over a problem with the compiler...)
The compiler puts this item in .sdata, for 32-bit. There is no .srodata,
so if it wants to use a small data section, it must use .sdata .
Non-external, non-referenced symbols are not put in .sdata, that is the
difference you see with the "static".
I don't think there is a bug here. If you think there is, please open
a GCC bug.
Segher
WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Kees Cook <keescook@chromium.org>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
Michael Ellerman <mpe@ellerman.id.au>,
Jinbum Park <jinb.park7@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only"
Date: Mon, 25 Sep 2017 02:37:21 -0500 [thread overview]
Message-ID: <20170925073721.GM8421@gate.crashing.org> (raw)
In-Reply-To: <CAGXu5jJ54+bCcXaPK1ExsxtTDPHNn1+1gywb3TDbe-SEtt1zuQ@mail.gmail.com>
On Sun, Sep 24, 2017 at 12:17:51PM -0700, Kees Cook wrote:
> On Thu, Sep 21, 2017 at 2:37 AM, Christophe Leroy
> <christophe.leroy@c-s.fr> wrote:
> > On powerpc, RODATA_TEST fails with message the following messages:
> >
> > [ 6.199505] Freeing unused kernel memory: 528K
> > [ 6.203935] rodata_test: test data was not read only
> >
> > This is because GCC allocates it to .data section:
> >
> > c0695034 g O .data 00000004 rodata_test_data
>
> Uuuh... that seems like a compiler bug. It's marked "const" -- it
> should never end up in .data. I would argue that this has done exactly
> what it was supposed to do, and shows that something has gone wrong.
> It should always be const. Adding "static" should just change
> visibility. (I'm not opposed to the static change, but it seems to
> paper over a problem with the compiler...)
The compiler puts this item in .sdata, for 32-bit. There is no .srodata,
so if it wants to use a small data section, it must use .sdata .
Non-external, non-referenced symbols are not put in .sdata, that is the
difference you see with the "static".
I don't think there is a bug here. If you think there is, please open
a GCC bug.
Segher
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next prev parent reply other threads:[~2017-09-25 7:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-21 9:37 [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only" Christophe Leroy
2017-09-21 9:37 ` Christophe Leroy
2017-09-24 19:17 ` Kees Cook
2017-09-24 19:17 ` Kees Cook
2017-09-25 7:37 ` Segher Boessenkool [this message]
2017-09-25 7:37 ` Segher Boessenkool
2017-09-25 16:01 ` David Laight
2017-09-25 16:01 ` David Laight
2017-09-25 16:01 ` David Laight
2017-09-25 19:41 ` Segher Boessenkool
2017-09-25 19:41 ` Segher Boessenkool
2017-10-02 19:29 ` Kees Cook
2017-10-02 19:29 ` Kees Cook
2017-10-02 20:08 ` Segher Boessenkool
2017-10-02 20:08 ` Segher Boessenkool
2017-10-02 20:27 ` Kees Cook
2017-10-02 20:27 ` Kees Cook
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