linux-kernel - Re: [PATCH 2/3] kallsyms: Add APIs to match symbol without .llmv.<hash> suffix.

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Message-ID: <17533605-ec23-d806-2759-a054492384e4@huaweicloud.com>
Date: Fri, 2 Aug 2024 14:53:47 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...weicloud.com>
To: Song Liu <songliubraving@...a.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Song Liu <song@...nel.org>,
 "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>,
 "linux-trace-kernel@...r.kernel.org" <linux-trace-kernel@...r.kernel.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Jiri Kosina <jikos@...nel.org>,
 Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.com>,
 Joe Lawrence <joe.lawrence@...hat.com>, Nathan Chancellor
 <nathan@...nel.org>, "morbo@...gle.com" <morbo@...gle.com>,
 Justin Stitt <justinstitt@...gle.com>, Luis Chamberlain <mcgrof@...nel.org>,
 Leizhen <thunder.leizhen@...wei.com>, "kees@...nel.org" <kees@...nel.org>,
 Kernel Team <kernel-team@...a.com>, Matthew Maurer <mmaurer@...gle.com>,
 Sami Tolvanen <samitolvanen@...gle.com>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/3] kallsyms: Add APIs to match symbol without
 .llmv.<hash> suffix.

On 2024/8/2 11:45, Song Liu wrote:
> 
> 
>> On Aug 1, 2024, at 6:18 PM, Leizhen (ThunderTown) <thunder.leizhen@...weicloud.com> wrote:
>>
>> On 2024/7/31 9:00, Song Liu wrote:
>>> Hi Masami, 
>>>
>>>> On Jul 30, 2024, at 6:03 AM, Masami Hiramatsu <mhiramat@...nel.org> wrote:
>>>>
>>>> On Mon, 29 Jul 2024 17:54:32 -0700
>>>> Song Liu <song@...nel.org> wrote:
>>>>
>>>>> With CONFIG_LTO_CLANG=y, the compiler may add suffix to function names
>>>>> to avoid duplication. This causes confusion with users of kallsyms.
>>>>> On one hand, users like livepatch are required to match the symbols
>>>>> exactly. On the other hand, users like kprobe would like to match to
>>>>> original function names.
>>>>>
>>>>> Solve this by splitting kallsyms APIs. Specifically, existing APIs now
>>>>> should match the symbols exactly. Add two APIs that matches the full
>>>>> symbol, or only the part without .llvm.suffix. Specifically, the following
>>>>> two APIs are added:
>>>>>
>>>>> 1. kallsyms_lookup_name_or_prefix()
>>>>> 2. kallsyms_on_each_match_symbol_or_prefix()
>>>>
>>>> Since this API only removes the suffix, "match prefix" is a bit confusing.
>>>> (this sounds like matching "foo" with "foo" and "foo_bar", but in reality,
>>>> it only matches "foo" and "foo.llvm.*")
>>>> What about the name below?
>>>>
>>>> kallsyms_lookup_name_without_suffix()
>>>> kallsyms_on_each_match_symbol_without_suffix()
>>>
>>> I am open to name suggestions. I named it as xx or prefix to highlight
>>> that these two APIs will try match full name first, and they only match
>>> the symbol without suffix when there is no full name match. 
>>>
>>> Maybe we can call them: 
>>> - kallsyms_lookup_name_or_without_suffix()
>>> - kallsyms_on_each_match_symbol_or_without_suffix()
>>>
>>> Again, I am open to any name selections here.
>>
>> Only static functions have suffixes. In my opinion, explicitly marking static
>> might be a little clearer.
>> kallsyms_lookup_static_name()
>> kallsyms_on_each_match_static_symbol()
> 
> While these names are shorter, I think they are more confusing. Not all
> folks know that only static functions can have suffixes. 
> 
> Maybe we should not hide the "try match full name first first" in the
> API, and let the users handle it. Then, we can safely call the new APIs
> *_without_suffix(), as Masami suggested. 

Yes, that would be clearer.

> 
> If there is no objections, I will send v2 based on this direction. 
> 
> Thanks,
> Song
> 

-- 
Regards,
  Zhen Lei