From: Borislav Petkov <bp@alien8.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
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 10:27:12 +0100 [thread overview]
Message-ID: <20150326092712.GA27751@pd.tnic> (raw)
In-Reply-To: <CA+55aFyJg1248Df6tj6KMA2o2KCQbZJ7i6POCPureVwzX91Dzg@mail.gmail.com>
On Wed, Mar 25, 2015 at 05:05:50PM -0700, Linus Torvalds wrote:
> so 'as' is clearly just stupid. It already takes the size of the
> constant into account and generates different instructions. Why not
> for the common 32-bit case too?
I think the destination register mandates which insn to use:
mov $0x12345678, %rdi
mov $0x12345678, %edi
...
15: 48 c7 c7 78 56 34 12 mov $0x12345678,%rdi
1c: bf 78 56 34 12 mov $0x12345678,%edi
and 'as' is perhaps not insolent enough to go and change it when seeing
the 32-bit constant.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
next prev parent reply other threads:[~2015-03-26 9:29 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 [this message]
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
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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