linux-kernel - Re: [PATCH 3/4] x86: open-code register save/restore in trace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrWwnfU9roXp_0Z_hHo-c2LMcc3_KRKJgx_=p2U-+i5PrA@mail.gmail.com>
Date:	Sat, 10 Jan 2015 13:02:18 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 3/4] x86: open-code register save/restore in
 trace_hardirqs thunks

On Sat, Jan 10, 2015 at 12:42 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Sat, Jan 10, 2015 at 12:17:13PM -0800, Andy Lutomirski wrote:
>> I asked this once, and someone told me that push/pop has lower
>> throughput.  I find this surprising.
>
> Implicit dependency on %rsp probably. The MOVs allow you to start more
> stuff out-of-order I'd guess...

AIUI modern CPUs have fancy stack engines that match call/ret pairs,
and presumably they can speculate rsp values across multiple pushes
and pops very quickly.

Also, don't compilers generally use push and pop to save and restore
callee-saved registers?  I think that function calls are common enough
that the CPU vendors would have made these sequences fast.

--Andy

>
>> Tt could be worth adding a macro along the lines of pushq_cfi_save
>> that does the pushq_cfi and the CFI_REL_OFFSET.
>
> Yep, for balance.
>
> --
> Regards/Gruss,
>     Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --



-- 
Andy Lutomirski
AMA Capital Management, LLC
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/