From: David Laight <David.Laight@ACULAB.COM>
To: 'Michael Ellerman' <mpe@ellerman.id.au>,
Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Kees Cook <keescook@chromium.org>
Cc: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
"linux-hardening@vger.kernel.org"
<linux-hardening@vger.kernel.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>
Subject: RE: mainline build failure of powerpc allmodconfig for prom_init_check
Date: Mon, 18 Jul 2022 07:51:45 +0000 [thread overview]
Message-ID: <72a95f0949d149d1b07bd161f3d59cc1@AcuMS.aculab.com> (raw)
In-Reply-To: <87cze3docs.fsf@mpe.ellerman.id.au>
From: Michael Ellerman
> Sent: 18 July 2022 05:41
...
> So we're memsetting all of args to 254, not zero.
>
> That's happening because allmodconfig with gcc 12 enables
> CONFIG_INIT_STACK_ALL_PATTERN, whereas gcc 11 doesn't.
I can't help feeling it would be better if that generated
a call to a memset64() function.
Saving loads of tests at the top of the function,
and (most of?) the constant expansion to 64bit.
Although and explicit 'stack clear' function would be better
for the kernel - since it would give the option of patching
it away at startup.
I really can't help feeling that initialising on-stack
arrays will kill performance.
While kernel stack frames have to be relatively small,
in userspace very large on-stack arrays can be allocated
(and correctly bound checked) knowing that the cost is
minimal (maybe a TLB miss).
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-07-18 7:51 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-14 8:55 mainline build failure of powerpc allmodconfig for prom_init_check Sudip Mukherjee (Codethink)
2022-07-17 9:12 ` Sudip Mukherjee
2022-07-17 14:44 ` Linus Torvalds
2022-07-17 19:54 ` Segher Boessenkool
2022-07-18 3:52 ` Michael Ellerman
2022-07-18 14:56 ` Segher Boessenkool
2022-07-17 20:25 ` Sudip Mukherjee
2022-07-17 20:29 ` Linus Torvalds
2022-07-17 20:38 ` Sudip Mukherjee
2022-07-17 20:56 ` Linus Torvalds
2022-07-17 20:56 ` Segher Boessenkool
2022-07-17 21:11 ` Linus Torvalds
2022-07-17 21:45 ` Segher Boessenkool
2022-07-18 1:38 ` Linus Torvalds
2022-07-18 4:41 ` Michael Ellerman
2022-07-18 7:51 ` David Laight [this message]
2022-07-18 13:44 ` [PATCH] powerpc/64s: Disable stack variable initialisation for prom_init Michael Ellerman
2022-07-18 15:03 ` Sudip Mukherjee
2022-07-18 18:34 ` Linus Torvalds
2022-07-18 19:06 ` mainline build failure of powerpc allmodconfig for prom_init_check Linus Torvalds
2022-07-18 22:08 ` Segher Boessenkool
2022-07-18 22:55 ` Linus Torvalds
2022-07-19 13:35 ` Michael Ellerman
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