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

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Message-ID: <CANiq72n5hg-ZyGV4oEca9iCbmQByanFUpNTkS=QmE1k8MUBR8w@mail.gmail.com>
Date: Wed, 3 Sep 2025 12:28:20 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
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 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

> (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.

> +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.

I hope this helps!

Cheers,
Miguel