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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Brian Gerst <brgerst@gmail.com>, Ingo Molnar <mingo@kernel.org>,
	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 7/9] x86/asm/entry/32: tidy up some instructions
Date: Wed, 1 Apr 2015 15:14:17 -0700	[thread overview]
Message-ID: <CA+55aFweqq2bM7KKJkt1zOWMrDxfu-WVXmCD0Seut3y-o0Bf=w@mail.gmail.com> (raw)
In-Reply-To: <551C5A73.3050109@redhat.com>

On Wed, Apr 1, 2015 at 1:52 PM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>
> BTW, AMD64 docs do explicitly say that MOVs from segment registers
> to gpregs are zero-extending.

Yeah, I think anything even *remotely* recent enough to do 64-bit does
zero-extending.

Even on the 32-bit side, anything that does register renaming is much
better off with zero-extension than with partial register writes.

And I found the "push" thing. It's actually documented:

  "When pushing a segment selector onto the stack, the Pentium 4,
Intel Xeon, P6 family, and Intel486 processors
decrement the ESP register by the operand size and then write 2 bytes.
If the operand size is 32-bits, the upper
two bytes of the write are not modified"

but I can't find any similar documentation for the "mov
Sreg->register" thing. So now I'm starting to doubt my own memory.

                          Linus

  parent reply	other threads:[~2015-04-01 22:14 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-31 17:00 [PATCH 1/9] x86/asm/entry/64: do not TRACE_IRQS fast SYSRET64 path Denys Vlasenko
2015-03-31 17:00 ` [PATCH 2/9] x86/asm/entry/32: Use PUSH instructions to build pt_regs on stack Denys Vlasenko
2015-04-01  8:51   ` Ingo Molnar
2015-04-01 13:12     ` Denys Vlasenko
2015-04-01 13:21       ` Ingo Molnar
2015-04-01 13:53       ` Borislav Petkov
2015-04-02 12:25   ` [tip:x86/asm] x86/asm/entry/32: Use smaller PUSH instructions instead of MOV, to build 'pt_regs' " tip-bot for Denys Vlasenko
2015-03-31 17:00 ` [PATCH 3/9] x86/asm/entry/64: simplify retint_kernel label usage, make retint_restore_args label local Denys Vlasenko
2015-04-02 12:25   ` [tip:x86/asm] x86/asm/entry/64: Simplify " tip-bot for Denys Vlasenko
2015-03-31 17:00 ` [PATCH 4/9] x86/asm/entry/64: remove redundant DISABLE_INTERRUPTS Denys Vlasenko
2015-04-02 12:25   ` [tip:x86/asm] x86/asm/entry/64: Remove redundant DISABLE_INTERRUPTS() tip-bot for Denys Vlasenko
2015-03-31 17:00 ` [PATCH 5/9] x86/asm/entry/64: simplify looping around preempt_schedule_irq Denys Vlasenko
2015-04-02 12:26   ` [tip:x86/asm] x86/asm/entry/64: Simplify looping around preempt_schedule_irq() tip-bot for Denys Vlasenko
2015-03-31 17:00 ` [PATCH 6/9] x86/asm/entry/64: tidy up some instructions Denys Vlasenko
2015-03-31 17:00 ` [PATCH 7/9] x86/asm/entry/32: " Denys Vlasenko
2015-03-31 22:21   ` Brian Gerst
2015-03-31 23:09     ` Linus Torvalds
2015-04-01 11:10     ` Denys Vlasenko
2015-04-01 15:50       ` Linus Torvalds
2015-04-01 20:52         ` Denys Vlasenko
2015-04-01 20:57           ` H. Peter Anvin
2015-04-01 22:14           ` Linus Torvalds [this message]
2015-04-02  0:32             ` Brian Gerst
2015-04-01  8:29   ` Ingo Molnar
2015-03-31 17:00 ` [PATCH 8/9] x86/asm: replace MOVQ $imm,%reg with MOVL Denys Vlasenko
2015-04-02 12:26   ` [tip:x86/asm] x86/asm: Replace "MOVQ $imm, %reg" " tip-bot for Denys Vlasenko
2015-03-31 17:00 ` [PATCH 9/9] x86/asm/entry/64: use local label to skip around sycall dispatch Denys Vlasenko
2015-04-02 12:26   ` [tip:x86/asm] x86/asm/entry/64: Use " tip-bot for Denys Vlasenko
2015-04-02 12:25 ` [tip:x86/asm] x86/asm/entry/64: Do not TRACE_IRQS fast SYSRET64 path tip-bot for Denys Vlasenko

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