linux-kernel - Re: [PATCH v2 5/5] LoongArch: Enable jump table with GCC for objtool

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Message-ID: <7e8adb0b-e681-72ae-40d8-740dc3f9480b@loongson.cn>
Date: Tue, 12 Nov 2024 20:26:56 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Xi Ruoyao <xry111@...111.site>, Peter Zijlstra <peterz@...radead.org>
Cc: Huacai Chen <chenhuacai@...nel.org>, Josh Poimboeuf
 <jpoimboe@...nel.org>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] LoongArch: Enable jump table with GCC for objtool

On 11/12/2024 11:15 AM, Xi Ruoyao wrote:
> On Wed, 2024-11-06 at 13:03 +0800, Tiezhu Yang wrote:
>> On 11/05/2024 10:15 PM, Peter Zijlstra wrote:
>>> On Tue, Nov 05, 2024 at 08:39:06PM +0800, Tiezhu Yang wrote:
>>>> For now, it is time to remove the compiler option -fno-jump-tables
>>>> to enable jump table for objtool if the compiler is GCC and it has
>>>> the compiler option -mannotate-tablejump, otherwise still keep the
>>>> compiler option -fno-jump-tables to maintain compatibility with the
>>>> older compilers.

...

>> ifdef CONFIG_CC_HAS_ANNOTATE_TABLEJUMP
>> KBUILD_CFLAGS                   += $(call cc-option,-mannotate-tablejump)
>> else
>> KBUILD_CFLAGS                   += -fno-jump-tables
>> endif
>
> Has -mannotate-tablejump been added to Clang?

Yes.

> IMO it's better to add it
> to Clang first, and add Clang & GCC support at once into objtool.

Looks reasonable, the fact is that there are some corner issues
compiled with Clang due to different compiler behaviors, most of
the issues have been addressed and I need to do more test, I will
send v3 with about 10 patches after the coming merge window.

Thanks,
Tiezhu