From: Denys Vlasenko <dvlasenk@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
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, 01 Apr 2015 22:52:03 +0200 [thread overview]
Message-ID: <551C5A73.3050109@redhat.com> (raw)
In-Reply-To: <CA+55aFxuZvO=RjMGFm9Ng3ph1oKoARK4ZHdBotHsjpbKPs6qEQ@mail.gmail.com>
On 04/01/2015 05:50 PM, Linus Torvalds wrote:
> On Wed, Apr 1, 2015 at 4:10 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>>
>> I did not know that. I was sure they are always zero extended.
>
> On all half-way modern cpu's they are. But on some older cpu's
> (possibly just the original 386) the segment move instructions
> basically are always 16-bit, and the operand size is ignored (so the
> 32-bit version is just smaller and faster to decode, because it
> doesn't have a 16-bit operand size prefix)
>
> Iirc, the same is true for the values pushed to memory on exceptions,
> so the 'cs/ss' values on the exception stack may not be reliable in
> the upper 16 bits.
>
> I don't remember if the same might be true of "pushl %Sseg". The intel
> architecture manual says segment registers are zero-extended on push.
BTW, AMD64 docs do explicitly say that MOVs from segment registers
to gpregs are zero-extending.
next prev parent reply other threads:[~2015-04-01 20:52 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 [this message]
2015-04-01 20:57 ` H. Peter Anvin
2015-04-01 22:14 ` Linus Torvalds
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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