linux-kernel - Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW

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Date: Wed, 15 May 2024 17:30:21 +0800
From: maobibo <maobibo@...ngson.cn>
To: Arnd Bergmann <arnd@...db.de>, Huacai Chen <chenhuacai@...ngson.cn>,
 Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, Linux-Arch <linux-arch@...r.kernel.org>,
 Xuefeng Li <lixuefeng@...ngson.cn>, guoren <guoren@...nel.org>,
 WANG Xuerui <kernel@...0n.name>, Jiaxun Yang <jiaxun.yang@...goat.com>,
 linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn,
 stable@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW_STAT in unistd.h



On 2024/5/11 下午8:17, Arnd Bergmann wrote:
> On Sat, May 11, 2024, at 12:01, Huacai Chen wrote:
>> Chromium sandbox apparently wants to deny statx [1] so it could properly
>> inspect arguments after the sandboxed process later falls back to fstat.
>> Because there's currently not a "fd-only" version of statx, so that the
>> sandbox has no way to ensure the path argument is empty without being
>> able to peek into the sandboxed process's memory. For architectures able
>> to do newfstatat though, glibc falls back to newfstatat after getting
>> -ENOSYS for statx, then the respective SIGSYS handler [2] takes care of
>> inspecting the path argument, transforming allowed newfstatat's into
>> fstat instead which is allowed and has the same type of return value.
>>
>> But, as LoongArch is the first architecture to not have fstat nor
>> newfstatat, the LoongArch glibc does not attempt falling back at all
>> when it gets -ENOSYS for statx -- and you see the problem there!
> 
> My main objection here is that this is inconsistent with 32-bit
> architectures: we normally have newfstatat() on 64-bit
> architectures but fstatat64() on 32-bit ones. While loongarch64
> is the first 64-bit one that is missing newfstatat(), we have
> riscv32 already without fstatat64().
> 
> Importantly, we can't just add fstatat64() on riscv32 because
> there is no time64 version for it other than statx(), and I don't
> want the architectures to diverge more than necessary.
yes, I agree. Normally there is newfstatat() on 64-bit architectures but 
fstatat64() on 32-bit ones.

I do not understand why fstatat64() can be added for riscv32 still.
32bit timestamp seems works well for the present, it is valid until
(0x1UL << 32) / 365 / 24 / 3600 + 1970 == 2106 year. Year 2106 should
be enough for 32bit system.

Regards
Bibo Mao


> I would not mind adding a variant of statx() that works for
> both riscv32 and loongarch64 though, if it gets added to all
> architectures.
> 
>        Arnd
>