linux-kernel - Re: [RFC PATCH 3/3] LoongArch: Handle table jump option for RUST

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Message-ID: <e9e9b127-3237-92d1-891c-84fc5e6bfcdd@loongson.cn>
Date: Thu, 4 Sep 2025 11:57:53 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Huacai Chen <chenhuacai@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
 WANG Rui <wangrui@...ngson.cn>, rust-for-linux@...r.kernel.org,
 loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] LoongArch: Handle table jump option for RUST

On 2025/9/3 下午6:28, Miguel Ojeda wrote:
> On Wed, Sep 3, 2025 at 11:53 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>>
>> When compiling with LLVM and CONFIG_RUST is set, there exist objtool
>> warnings "sibling call from callable instruction with modified stack
>> frame" in rust/core.o and rust/kernel.o.
> 
> Thanks for fixing this! I have seen it for a long time in my CI:
> 
> I think this is:
> 
>      Reported-by: Miguel Ojeda <ojeda@...nel.org>
>      Closes: https://lore.kernel.org/rust-for-linux/CANiq72mNeCuPkCDrG2db3w=AX+O-zYrfprisDPmRac_qh65Dmg@mail.gmail.com/
> 
> Perhaps consider adding an example of the warning in the log for
> future Lore searches:
> 
>      rust/core.o: warning: objtool:
> _RNvXs1_NtNtCs5QSdWC790r4_4core5ascii10ascii_charNtB5_9AsciiCharNtNtB9_3fmt5Debug3fmt+0x54:
> sibling call from callable instruction with modified stack frame

OK, will update the commit message in the next version.

>> (1) Please install rustc 1.78.0 (without annotate-tablejump option) or
>> 1.87.0 (with annotate-tablejump option), do not use the latest version
>> for now, otherwise there may be build error:
> 
> Nightly is not a released version, and it is expected that it breaks
> from time to time. Even beta may break. We are ~2 months away from
> that release.
> 
> In any case, I don't think this information is related to this commit.

OK, I will remove the above info in the commit message.

>> +config RUSTC_HAS_ANNOTATE_TABLEJUMP
>> +       depends on RUST
>> +       def_bool $(rustc-option,-Cllvm-args=--loongarch-annotate-tablejump)
> 
> I think this may be fine given it is `-Cllvm-args` and anyway
> LoongArch doesn't use a `target.json` (which is great!), but please
> double-check reading what I wrote in 46e24a545cdb ("rust:
> kasan/kbuild: fix missing flags on first build") just in case.

OK, will do.

Thanks,
Tiezhu