linux-kernel - Re: [RFC PATCH 0/4] Add jump table support for objtool on LoongArch

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Message-ID: <307bcd3e-f4fe-8cc0-c557-4069c97c6072@loongson.cn>
Date: Fri, 12 Jul 2024 18:19:34 +0800
From: Jinyang He <hejinyang@...ngson.cn>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>, Josh Poimboeuf
 <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Huacai Chen <chenhuacai@...nel.org>
Cc: Xi Ruoyao <xry111@...111.site>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/4] Add jump table support for objtool on LoongArch

Are we always avoid our problems?

1, When text section not support "R_LARCH_32_PCREL", update compiler
    to add AS_HAS_THIN_ADD_SUB.
2, When not support jump-table, use "-fno-jump-tables" to avoid it,
    (and now update compiler to add CC_HAS_ANNOTATE_TABLEJUMP).
3, When not support relax, use "-mno-relax" to avoid it.
4, When some where in asm can be backtraced but generate warning,
    use STACK_FRAME_NON_STANDARD to avoid it.
5, When the goto-table cannot be handled (I guess the Ruoyao's
    patch cannot handle goto table), use CONFIG_BPF_JIT_ALWAYS_ON
    to avoid compile ___bpf_prog_run.
6, And other $fp warnings not be solved in clang. Do we only care gcc?

So how to do in the future if compilers have other changed? Do we
need update compilers (both gcc and clang) again and again? Why
not just update objtool codes to solves these problems? As many
RISC arch not support directly find jump table, can we support
more generic ways to find it?

On 2024-07-12 17:15, Tiezhu Yang wrote:
> This RFC version is based on Linux 6.10-rc7, there are no detailed
> commit messages for each patch for now and the code are relatively
> clear and simple.
>
> This series is tested with the latest upstream gcc applied with patch
> "LoongArch: Add support to annotate tablejump" [1] which adds a new
> section discard.tablejump_annotate to record the jump info, it makes
> life much easier, special thanks to Ruoyao.
>
> I will address all the review comments and update the commit messages
> after the merge window.
>
> [1] https://inbox.sourceware.org/gcc-patches/20240711114415.4420-1-xry111@xry111.site/
>
> Tiezhu Yang (4):
>    objtool: Check local label in find_jump_table()
>    objtool: Check various types in add_jump_table()
>    objtool/LoongArch: Add support for jump table
>    LoongArch: Remove -fno-jump-tables for objtool
>
>   arch/loongarch/Kconfig                 |  8 +++-
>   arch/loongarch/Makefile                |  6 +--
>   tools/objtool/arch/loongarch/special.c | 54 +++++++++++++++++++++++++-
>   tools/objtool/check.c                  | 36 +++++++++++++++--
>   4 files changed, 94 insertions(+), 10 deletions(-)
>