From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>,
linux@sandersweb.net, linux-kernel@vger.kernel.org,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [BUG] x86 kenel won't boot under Virtual PC
Date: Mon, 08 Sep 2008 12:09:56 -0700 [thread overview]
Message-ID: <48C57884.30607@zytor.com> (raw)
In-Reply-To: <alpine.LFD.1.10.0809081028590.3117@nehalem.linux-foundation.org>
[-- Attachment #1: Type: text/plain, Size: 1408 bytes --]
Linus Torvalds wrote:
>>>
>> Yes, it does:
>>
>> /* We need to decide which NOP sequence to use for 32bit and
>> 64bit. When -mtune= is used:
>>
>> 1. For PROCESSOR_I386, PROCESSOR_I486, PROCESSOR_PENTIUM and
>> PROCESSOR_GENERIC32, f32_patt will be used.
>> 2. For PROCESSOR_PENTIUMPRO, PROCESSOR_PENTIUM4, PROCESSOR_NOCONA,
>> PROCESSOR_CORE, PROCESSOR_CORE2, and PROCESSOR_GENERIC64,
>> alt_long_patt will be used.
>> 3. For PROCESSOR_ATHLON, PROCESSOR_K6, PROCESSOR_K8 and
>> PROCESSOR_AMDFAM10, alt_short_patt will be used.
>>
>> When -mtune= isn't used, alt_long_patt will be used if
>> cpu_arch_isa_flags has Cpu686. Otherwise, f32_patt will
>> be used.
>>
>> "alt_long_patt" uses NOPL and its variants.
>
> That is A TOTAL PIECE OF SH*T, and against gcc's own documentation.
>
> "-mtune=x" is very much defined to be a performance _tuning_ option, not
> an "architectural" option.
>
> Quite frankly, this is a gcc bug. Plain and simple.
>
OK, digging some more into this garbage...
Apparently the situation isn't quite as dire as it first seems.
At least gcc 4.3.0 doesn't actually pass -mtune= to gas; it just drops
the option on the floor. This means this bug isn't manifest when
calling from gcc (as opposed to invoking as directly.)
However, I would still like to push the following patch to be on the
safe side, ok?
-hpa
[-- Attachment #2: 0002-x86-prevent-binutils-from-being-smart-and-generat.patch --]
[-- Type: text/x-patch, Size: 1346 bytes --]
>From 0fbbf1008e5177677dbdb6292d94ec40df965d82 Mon Sep 17 00:00:00 2001
From: H. Peter Anvin <hpa@zytor.com>
Date: Mon, 8 Sep 2008 12:01:48 -0700
Subject: [PATCH] x86: prevent binutils from being "smart" and generating NOPLs for us
binutils, contrary to documented behaviour, will generate long NOPs (a
P6-or-higher instruction which is broken on at least some VIA chips,
Virtual PC/Virtual Server, and some versions of Qemu) depending on the
-mtune= option, which is not supposed to change architectural
behaviour.
Pass an explicit override to the assembler, in case ends up passing
the -mtune= parameter to gas (gcc 4.3.0 does not appear to.)
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---
arch/x86/Makefile_32.cpu | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu
index e372b58..b72b4f7 100644
--- a/arch/x86/Makefile_32.cpu
+++ b/arch/x86/Makefile_32.cpu
@@ -45,3 +45,8 @@ cflags-$(CONFIG_MGEODEGX1) += -march=pentium-mmx
# cpu entries
cflags-$(CONFIG_X86_GENERIC) += $(call tune,generic,$(call tune,i686))
+# Bug fix for binutils: this option is required in order to keep
+# binutils from generating NOPL instructions against our will.
+ifneq ($(CONFIG_X86_P6_NOP),y)
+cflags-y += $(call cc-option,-Wa$(comma)-mtune=generic32,)
+endif
--
1.5.5.1
next prev parent reply other threads:[~2008-09-08 19:10 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-31 18:22 [BUG] x86 kenel won't boot under Virtual PC David Sanders
2008-08-31 18:47 ` Linus Torvalds
2008-08-31 19:27 ` Arjan van de Ven
2008-08-31 19:39 ` Linus Torvalds
2008-09-05 15:38 ` David Sanders
2008-09-05 16:15 ` Jan Beulich
2008-09-05 16:39 ` Linus Torvalds
2008-09-05 18:43 ` Ingo Molnar
2008-09-05 20:06 ` H. Peter Anvin
2008-09-05 19:08 ` Jeremy Fitzhardinge
2008-09-05 20:12 ` H. Peter Anvin
2008-09-05 16:30 ` Linus Torvalds
2008-09-05 17:55 ` Andi Kleen
2008-08-31 20:03 ` David Sanders
2008-09-01 20:23 ` David Sanders
2008-09-01 22:22 ` Linus Torvalds
2008-09-02 12:08 ` David Sanders
2008-09-02 18:12 ` Linus Torvalds
2008-09-02 18:44 ` David Sanders
2008-09-03 11:09 ` Peter Zijlstra
2008-09-03 11:20 ` David Sanders
[not found] ` <48C1C156.9080003@zytor.com>
2008-09-07 20:07 ` David Sanders
2008-09-07 23:22 ` David Sanders
2008-09-08 1:48 ` H. Peter Anvin
2008-09-08 2:49 ` David Sanders
2008-09-08 4:04 ` H. Peter Anvin
2008-09-08 9:42 ` Andi Kleen
2008-09-08 13:25 ` David Sanders
2008-09-08 15:09 ` Linus Torvalds
2008-09-08 15:23 ` Ingo Molnar
2008-09-08 15:36 ` H. Peter Anvin
2008-09-08 15:38 ` David Sanders
2008-09-08 15:38 ` H. Peter Anvin
2008-09-08 15:45 ` Andi Kleen
2008-09-08 15:43 ` H. Peter Anvin
2008-09-08 15:50 ` H. Peter Anvin
2008-09-08 15:50 ` Andi Kleen
2008-09-08 15:50 ` H. Peter Anvin
2008-09-08 15:57 ` Andi Kleen
2008-09-08 15:54 ` H. Peter Anvin
2008-09-08 16:07 ` Linus Torvalds
2008-09-08 16:13 ` H. Peter Anvin
2008-09-08 16:15 ` H. Peter Anvin
2008-09-08 16:26 ` David Sanders
2008-09-08 16:20 ` Linus Torvalds
2008-09-08 16:32 ` H. Peter Anvin
2008-09-08 17:02 ` Ingo Molnar
2008-09-08 16:34 ` david
2008-09-08 16:42 ` H. Peter Anvin
2008-09-08 18:51 ` david
2008-09-08 16:59 ` Linus Torvalds
2008-09-08 17:00 ` Andi Kleen
2008-09-08 17:04 ` Linus Torvalds
2008-09-08 17:08 ` H. Peter Anvin
2008-09-08 17:12 ` H. Peter Anvin
2008-09-08 17:41 ` Linus Torvalds
2008-09-08 17:38 ` Linus Torvalds
2008-09-08 17:59 ` H. Peter Anvin
2008-09-08 19:09 ` H. Peter Anvin [this message]
2008-09-08 22:42 ` Linus Torvalds
2008-09-08 17:18 ` Andi Kleen
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