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Date:   Mon, 18 Jul 2022 07:51:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Michael Ellerman' <>,
        Sudip Mukherjee <>,
        Benjamin Herrenschmidt <>,
        Paul Mackerras <>,
        Kees Cook <>
CC:     "" <>,
        linux-kernel <>,
        "" <>,
        "Linus Torvalds" <>
Subject: RE: mainline build failure of powerpc allmodconfig for

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).


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