linux-kernel - Re: [PATCH v2] LoongArch: Fix and simplify fcsr initialization on execve

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Date: Tue, 02 Jan 2024 18:25:54 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>
Cc: Eric Biederman <ebiederm@...ssion.com>, Kees Cook
 <keescook@...omium.org>,  Tiezhu Yang <yangtiezhu@...ngson.cn>, Jinyang He
 <hejinyang@...ngson.cn>, loongarch@...ts.linux.dev,  linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] LoongArch: Fix and simplify fcsr initialization on
 execve

On Tue, 2024-01-02 at 18:17 +0800, Xi Ruoyao wrote:
> The only other architecture setting FCSR in SET_PERSONALITY2 is MIPS.
> They do this for supporting different FP flavors (NaN encodings etc).
> which do not exist on LoongArch.  I'm not sure how MIPS evades the issue
> (or maybe it's just buggy too) but I'll investigate it later.

Phew.  I just managed to recommission my 3A4000 and I can reproduce the
issue as well with Linux 5.18.1 (the latest kernel release when I
decommissioned it) and CONFIG_PREEMPT=y.

% cat measure.c
#include <fenv.h>
int main() { return fetestexcept(FE_INEXACT); }

% echo $((1./3))
0.33333333333333331

% while ./a.out; do ; done
(stopped in seconds)

I'm building the mainline kernel on the 3A4000 now, will see if the
issue still exists...

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University