From: Borislav Petkov <bp@alien8.de>
To: David Laight <David.Laight@ACULAB.COM>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Andy Lutomirski <luto@amacapital.net>,
Nick Desaulniers <ndesaulniers@google.com>,
Andy Lutomirski <luto@kernel.org>,
Bill Wendling <morbo@google.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Greg Thelen <gthelen@google.com>,
John Sperbeck <jsperbeck@google.com>,
"# 3.4.x" <stable@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] x86/smap: Fix the smap_save() asm
Date: Thu, 17 Sep 2020 13:57:33 +0200 [thread overview]
Message-ID: <20200917115733.GH31960@zn.tnic> (raw)
In-Reply-To: <ec617df229514fbaa9897683ac88dfda@AcuMS.aculab.com>
On Thu, Sep 17, 2020 at 10:05:37AM +0000, David Laight wrote:
> The 'red-zone' allows leaf function to use stack memory for locals
> that is below (ie the wrong side of) the stack pointer.
After looking at
"Figure 3.3: Stack Frame with Base Pointer"
in the x86-64 ABI doc, you're probably right:
0(%rbp)
-8(%rbp)
...
0(%rsp)
.. red zone
-128(%rsp)
i.e., rsp-relative addresses with negative offsets are in the red zone.
So it looks like the compiler actually knows very well what's going on
here and allocates room on the stack for that 0x8(%rsp) slot.
Good.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-09-17 12:01 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 20:55 [PATCH] x86/smap: Fix the smap_save() asm Andy Lutomirski
2020-09-15 21:24 ` Nick Desaulniers
2020-09-15 21:31 ` Bill Wendling
2020-09-15 23:11 ` Andy Lutomirski
[not found] ` <7233f4cf-5b1d-0fca-0880-f1cf2e6e765b@citrix.com>
2020-09-15 23:43 ` Bill Wendling
2020-09-16 8:26 ` Borislav Petkov
[not found] ` <be498e49-b467-e04c-d833-372f7d83cb1f@citrix.com>
2020-09-17 6:04 ` Borislav Petkov
[not found] ` <ec617df229514fbaa9897683ac88dfda@AcuMS.aculab.com>
2020-09-17 11:57 ` Borislav Petkov [this message]
[not found] ` <823af5fadd464c48ade635498d07ba4e@AcuMS.aculab.com>
2020-09-17 14:39 ` Borislav Petkov
2020-09-17 16:32 ` Andy Lutomirski
2020-09-16 7:28 ` peterz
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