From: Nick Desaulniers <ndesaulniers@google.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
linux-fsdevel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Christoph Hellwig <hch@lst.de>,
Eric Dumazet <edumazet@google.com>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH] fs/select: avoid clang stack usage warning
Date: Tue, 11 Oct 2022 13:50:43 -0700 [thread overview]
Message-ID: <CAKwvOdnpMqW_esBd615Fx8VKTfny-yR2PTUejBH0uYkHaL517A@mail.gmail.com> (raw)
In-Reply-To: <f0dbc406-11b4-90f7-52fd-ce79f842c356@linux.intel.com>
On Fri, Oct 7, 2022 at 6:46 PM Andi Kleen <ak@linux.intel.com> wrote:
>
>
> On 10/6/2022 3:21 PM, Nick Desaulniers wrote:
> > On Thu, Mar 07, 2019 at 10:01:36AM +0100, Arnd Bergmann wrote:
> >> The select() implementation is carefully tuned to put a sensible amount
> >> of data on the stack for holding a copy of the user space fd_set,
> >> but not too large to risk overflowing the kernel stack.
> >>
> >> When building a 32-bit kernel with clang, we need a little more space
> >> than with gcc, which often triggers a warning:
> >>
> >> fs/select.c:619:5: error: stack frame size of 1048 bytes in function 'core_sys_select' [-Werror,-Wframe-larger-than=]
> >> int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
> >>
> >> I experimentally found that for 32-bit ARM, reducing the maximum
> >> stack usage by 64 bytes keeps us reliably under the warning limit
> >> again.
> >>
> >> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> >> ---
> >> include/linux/poll.h | 4 ++++
> >> 1 file changed, 4 insertions(+)
> >>
> >> diff --git a/include/linux/poll.h b/include/linux/poll.h
> >> index 7e0fdcf905d2..1cdc32b1f1b0 100644
> >> --- a/include/linux/poll.h
> >> +++ b/include/linux/poll.h
> >> @@ -16,7 +16,11 @@
> >> extern struct ctl_table epoll_table[]; /* for sysctl */
> >> /* ~832 bytes of stack space used max in sys_select/sys_poll before allocating
> >> additional memory. */
> >> +#ifdef __clang__
> >> +#define MAX_STACK_ALLOC 768
> > Hi Arnd,
> > Upon a toolchain upgrade for Android, our 32b x86 image used for
> > first-party developer VMs started tripping -Wframe-larger-than= again
> > (thanks -Werror) which is blocking our ability to upgrade our toolchain.
>
>
> I wonder if there is a way to disable the warning or increase the
> threshold just for this function. I don't think attribute optimize would
> work, but perhaps some pragma?
Here's what I would have guessed, the pragma approach seems a little broken.
https://godbolt.org/z/vY7fGYv7f
Maybe I'm holding it wrong?
>
>
> -Andi
>
>
>
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2022-10-11 20:51 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-07 9:01 [PATCH] fs/select: avoid clang stack usage warning Arnd Bergmann
2019-03-07 16:19 ` Andi Kleen
2022-10-06 22:21 ` Nick Desaulniers
2022-10-07 8:28 ` Arnd Bergmann
2022-10-07 19:04 ` Nick Desaulniers
2022-10-07 20:11 ` [PATCH] fs/select: mark do_select noinline_for_stack for 32b Nick Desaulniers
2022-10-10 7:44 ` Christoph Hellwig
2022-10-10 16:42 ` Nick Desaulniers
2022-10-10 19:55 ` Arnd Bergmann
2022-10-13 18:52 ` kernel test robot
2022-10-07 21:42 ` [PATCH] fs/select: avoid clang stack usage warning Arnd Bergmann
2022-10-07 22:54 ` Nick Desaulniers
2022-10-10 18:40 ` Nick Desaulniers
2022-10-11 12:46 ` Arnd Bergmann
2022-10-11 20:55 ` [PATCH v2] fs/select: mark do_select noinline_for_stack Nick Desaulniers
2022-10-14 22:39 ` Nathan Chancellor
2022-10-07 23:17 ` [PATCH] fs/select: avoid clang stack usage warning Kees Cook
2022-10-09 10:49 ` David Laight
2022-10-08 1:46 ` Andi Kleen
2022-10-11 20:50 ` Nick Desaulniers [this message]
2022-10-13 20:52 ` Andi Kleen
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