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

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Message-ID: <440AF603-49B0-435A-A59E-D5DDDD7BED88@fb.com>
Date: Fri, 2 Aug 2024 17:16:22 +0000
From: Song Liu <songliubraving@...a.com>
To: Song Liu <song@...nel.org>
CC: "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
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Subject: Re: [PATCH 2/3] kallsyms: Add APIs to match symbol without
 .llmv.<hash> suffix.



> On Jul 29, 2024, at 5:54 PM, 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()
> 
> These APIs will be used by kprobe.
> 
> Also cleanup some code and adjust kallsyms_selftests accordingly.
> 
> Signed-off-by: Song Liu <song@...nel.org>

Actually, if we only remove .llvm.<hash> suffix, but keep other .XXX
suffix, the *_without_suffx APIs will have the same issue Yonghong 
tried to fix in commit 33f0467fe06934d5e4ea6e24ce2b9c65ce618e26: 
binary search with symbols - .llvm.<hash> suffix is not correct. 
(Please see the commit log of 33f0467fe06934d5e4ea6e24ce2b9c65ce618e26 
for more details.)

I am updating the code to remove all .XXX suffix. This design will 
not have this issue. 

Thanks,
Song