From: Nathan Chancellor <nathan@kernel.org>
To: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Huacai Chen <chenhuacai@kernel.org>,
Miguel Ojeda <ojeda@kernel.org>, WANG Rui <wangrui@loongson.cn>,
rust-for-linux@vger.kernel.org, loongarch@lists.linux.dev,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH v1 1/2] LoongArch: Make LTO case independent in Makefile
Date: Mon, 22 Sep 2025 18:10:57 -0700 [thread overview]
Message-ID: <20250923011057.GA3980504@ax162> (raw)
In-Reply-To: <750c907d-cc95-5116-4507-52dd48927cec@loongson.cn>
> > > ifdef CONFIG_LTO_CLANG
> > > ifdef CONFIG_LLD_HAS_ANNOTATE_TABLEJUMP
> > > KBUILD_LDFLAGS += -mllvm --loongarch-annotate-tablejump
> > > else
> > > KBUILD_LDFLAGS += -mllvm --no-jump-tables
> > > endif
There is no '--no-jump-tables' LLVM option so this will not work.
Shouldn't -fno-jump-tables and -Zno-jump-tables take care of generating
jump tables?
> I do not know whether this is valid, you can test it with llvm 18
> and llvm 20 if you think it is a proper way.
For what it's worth, Huacai's original suggestion of
KBUILD_LDFLAGS += $(call ld-option,-mllvm --loongarch-annotate-tablejump)
appears to work for me and I do not see any objtool warnings with LTO
enabled but I might be missing something.
> But IIRC, there is objtool warning with llvm 18, I reported to llvm
> developer Wang Lei and he fixed it as the following commit:
>
> [LoongArch] Avoid indirect branch jumps using the ra register
> https://github.com/llvm/llvm-project/commit/21ef17c62645
>
> Actually, the above commit solved a performance issue of llvm compiler,
> so I prefer to update the minimal llvm version to 20 for LoongArch.
I tend to let architecture maintainers make the call around minimum
supported versions of compilers, so if that is how you would like to
proceed, I am fine with that. I will say LLVM 20 is pretty new (released
on March 4th, 2025) but I expect most of your users to probably be using
bleeding edge tools for all the changes you make in the compiler and
lower level libraries?
Cheers,
Nathan
next prev parent reply other threads:[~2025-09-23 1:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20250909092707.3127-1-yangtiezhu@loongson.cn>
[not found] ` <20250909092707.3127-2-yangtiezhu@loongson.cn>
2025-09-20 6:15 ` [PATCH v1 1/2] LoongArch: Make LTO case independent in Makefile Nathan Chancellor
2025-09-20 8:23 ` Huacai Chen
2025-09-20 9:19 ` Tiezhu Yang
2025-09-20 10:22 ` Tiezhu Yang
2025-09-20 11:41 ` Huacai Chen
2025-09-20 12:52 ` Tiezhu Yang
2025-09-23 1:10 ` Nathan Chancellor [this message]
2025-09-23 3:13 ` Tiezhu Yang
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