From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-fsdevel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Andi Kleen <ak@linux.intel.com>, 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: Thu, 6 Oct 2022 15:21:24 -0700 [thread overview]
Message-ID: <20221006222124.aabaemy7ofop7ccz@google.com> (raw)
In-Reply-To: <20190307090146.1874906-1-arnd@arndb.de>
[-- Attachment #1: Type: text/plain, Size: 2448 bytes --]
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've attached the zstd compressed .config file that reproduces with ToT
LLVM:
$ cd linux
$ zstd -d path/to/config.zst -o .config
$ make ARCH=i386 LLVM=1 -j128 fs/select.o
fs/select.c:625:5: error: stack frame size (1028) exceeds limit (1024)
in 'core_sys_select' [-Werror,-Wframe-larger-than]
int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
^
As you can see, we're just barely tipping over the limit. Should I send
a patch to reduce this again? If so, any thoughts by how much?
Decrementing the current value by 4 builds the config in question, but
seems brittle.
Do we need to only do this if !CONFIG_64BIT?
commit ad312f95d41c ("fs/select: avoid clang stack usage warning")
seems to allude to this being more problematic on 32b targets?
> +#else
> #define MAX_STACK_ALLOC 832
> +#endif
> #define FRONTEND_STACK_ALLOC 256
> #define SELECT_STACK_ALLOC FRONTEND_STACK_ALLOC
> #define POLL_STACK_ALLOC FRONTEND_STACK_ALLOC
> --
> 2.20.0
>
>
[-- Attachment #2: config.zst --]
[-- Type: application/zstd, Size: 45882 bytes --]
next parent reply other threads:[~2022-10-06 22:21 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190307090146.1874906-1-arnd@arndb.de>
2022-10-06 22:21 ` Nick Desaulniers [this message]
2022-10-07 8:28 ` [PATCH] fs/select: avoid clang stack usage warning 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
2022-10-13 20:52 ` Andi Kleen
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