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From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Oleg Nesterov <oleg@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Alexei Starovoitov <ast@plumgrid.com>,
	Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/4] x86/asm/entry/64: use smaller insns
Date: Thu, 26 Mar 2015 10:30:53 +0100	[thread overview]
Message-ID: <20150326093053.GB14706@gmail.com> (raw)
In-Reply-To: <CA+55aFwHuaj80NaRNZW3Jfzh7_=nsx5p5=07PXUpaYwLzH-T=Q@mail.gmail.com>


* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Wed, Mar 25, 2015 at 10:18 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
> > The $AUDIT_ARCH_X86_64 parameter to syscall_trace_enter_phase1/2
> > is a 32-bit constant, loading it with 32-bit MOV produces 5-byte insn
> > instead of 10-byte one.
> 
> Side note: has anybody talked to the assembler people? This would 
> seem to be very much something that the assembler could have noticed 
> and done on its own. [...]

Maybe GCC already picks a 32-bit opcode in these small-constant cases, 
so there was little incentive to optimize on the GAS side, other than 
making it correct.

> [...] It's a bit sad that we need to overspecify these things..

Yeah, that's sad.

Yesterday when I have read Denys's patch I double checked that there's 
no other similar (easily identifiable ...) movq opcode left in the 
64-bit entry code, so we seem to have squashed most of them.

Thanks,

	Ingo

  parent reply	other threads:[~2015-03-26  9:31 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-25 17:18 [PATCH 1/4] x86/asm/entry/64: better label name, fix comments Denys Vlasenko
2015-03-25 17:18 ` [PATCH 2/4] x86/asm/entry/64: do not TRACE_IRQS fast SYSRET64 path Denys Vlasenko
2015-03-25 17:29   ` Ingo Molnar
2015-03-25 17:41     ` Denys Vlasenko
2015-03-25 18:04       ` Ingo Molnar
2015-03-25 18:19         ` Denys Vlasenko
2015-03-25 17:18 ` [PATCH 3/4] x86/asm/entry/64: use smaller insns Denys Vlasenko
2015-03-25 18:03   ` Andy Lutomirski
2015-03-25 23:51   ` Linus Torvalds
2015-03-25 23:56     ` H. Peter Anvin
2015-03-26  0:05       ` Linus Torvalds
2015-03-26  0:12         ` H. Peter Anvin
2015-03-26  9:27         ` Borislav Petkov
2015-03-26  9:37           ` Ingo Molnar
2015-03-26  9:51             ` Borislav Petkov
2015-03-26 10:07             ` Denys Vlasenko
2015-03-26 10:25               ` Ingo Molnar
2015-03-26 10:53                 ` Denys Vlasenko
2015-03-26 10:25               ` Borislav Petkov
2015-03-26  9:30     ` Ingo Molnar [this message]
2015-03-27 11:47   ` [tip:x86/asm] x86/asm/entry/64: Use smaller instructions tip-bot for Denys Vlasenko
2015-03-25 17:18 ` [PATCH 4/4] x86/asm/entry/64: fix typo in comment Denys Vlasenko
2015-03-27 11:46 ` [tip:x86/asm] x86/asm/entry/64: Use better label name, fix comments tip-bot for Denys Vlasenko
2015-03-27 12:15   ` Borislav Petkov

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