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Message-ID: <72a95f0949d149d1b07bd161f3d59cc1@AcuMS.aculab.com> Date: Mon, 18 Jul 2022 07:51:45 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Michael Ellerman' <mpe@...erman.id.au>, Sudip Mukherjee <sudipm.mukherjee@...il.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Kees Cook <keescook@...omium.org> CC: "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, linux-kernel <linux-kernel@...r.kernel.org>, "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>, "Linus Torvalds" <torvalds@...ux-foundation.org> Subject: RE: mainline build failure of powerpc allmodconfig for prom_init_check 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)
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