linux-kernel - Re: [PATCH] x86: add hintable NOPs emulation

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Message-ID: <77c08318-f67d-42e0-8745-6a999e2e9f62@orca.pet>
Date: Thu, 21 Aug 2025 11:35:01 +0200
From: Marcos Del Sol Vives <marcos@...a.pet>
To: "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, Brian Gerst <brgerst@...il.com>,
 Uros Bizjak <ubizjak@...il.com>, Ard Biesheuvel <ardb@...nel.org>,
 David Kaplan <david.kaplan@....com>, "Ahmed S. Darwish"
 <darwi@...utronix.de>, Kees Cook <kees@...nel.org>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Andrew Cooper <andrew.cooper3@...rix.com>, Oleg Nesterov <oleg@...hat.com>,
 "Xin Li (Intel)" <xin@...or.com>, Sabyrzhan Tasbolatov <snovitoll@...il.com>
Subject: Re: [PATCH] x86: add hintable NOPs emulation

El 21/08/2025 a las 3:43, H. Peter Anvin escribió:
> On August 19, 2025 6:34:46 PM PDT, Marcos Del Sol Vives <marcos@...a.pet> wrote:
>> One such software is sudo in Debian bookworm, which is compiled with
>> GCC -fcf-protection=branch and contains ENDBR32 instructions. It crashes
>> on my Vortex86DX3 processor and VIA C3 Nehalem processors [1].
>>
>> This patch is a much simplified version of my previous patch for x86
>> instruction emulation [2], that only emulates hintable NOPs.
>>
>> [1]: https://lists.debian.org/debian-devel/2023/10/msg00118.html
>> [2]: https://lore.kernel.org/all/20210626130313.1283485-1-marcos@orca.pet/
>
> Do those processors support FCOMI?

The Vortex86DX3, at the very least, does. Unlike the Vortex86MX I wrote the
previous patch for, this one seems to support all standard i686
instructions. It's modern enough to support SSE1, even.

I have tested it using the program I wrote for testing it on the -MX
last time: https://lore.kernel.org/all/b69e0c78-81eb-0d4d-dce5-076b5f239e28@orca.pet/.

> marcos@...3:~$ LANG=C gcc -Wall fucomi-test.c -o fucomi-test
> marcos@...3:~$ ./fucomi-test
> Float value: 6.210000
> FPU status: 3800 EFLAGS: 00000242

Which matches 1:1 my current desktop Ryzen 8645H.

Greetings,
Marcos