linux-kernel - Re: [PATCH v3 0/2] Fix kallsyms with CONFIG_LTO

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Message-ID: <0C1544B6-60CF-44DC-A10C-73F1504F81D1@fb.com>
Date: Tue, 13 Aug 2024 21:20:48 +0000
From: Song Liu <songliubraving@...a.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
CC: Song Liu <song@...nel.org>,
        "live-patching@...r.kernel.org"
	<live-patching@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
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Subject: Re: [PATCH v3 0/2] Fix kallsyms with CONFIG_LTO_CLANG

Hi Masami, 

Thanks for your review and test!

@Sami, could you please also review the set?

@Luis, I replied to 1/2 and 2/2 with Fixes tags that I think make most 
sense. Please let me know if we need changes to the set or more reviews
and tests. 

Thanks,
Song

> On Aug 12, 2024, at 9:29 PM, Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> On Wed,  7 Aug 2024 15:05:11 -0700
> Song Liu <song@...nel.org> wrote:
> 
>> With CONFIG_LTO_CLANG, the compiler/linker adds .llvm.<hash> suffix to
>> local symbols to avoid duplications. Existing scripts/kallsyms sorts
>> symbols without .llvm.<hash> suffix. However, this causes quite some
>> issues later on. Some users of kallsyms, such as livepatch, have to match
>> symbols exactly.
>> 
>> Address this by sorting full symbols at build time, and let kallsyms
>> lookup APIs to match the symbols exactly.
>> 
> 
> I've tested this series and confirmed it makes kprobes work with llvm suffixed
> symbols.
> 
> /sys/kernel/tracing # echo "p c_start.llvm.8011538628216713357" >> kprobe_events
> /sys/kernel/tracing # cat kprobe_events 
> p:kprobes/p_c_start_llvm_8011538628216713357_0 c_start.llvm.8011538628216713357
> /sys/kernel/tracing # echo "p c_start" >> kprobe_events 
> /sys/kernel/tracing # cat kprobe_events 
> p:kprobes/p_c_start_llvm_8011538628216713357_0 c_start.llvm.8011538628216713357
> p:kprobes/p_c_start_0 c_start
> 
> And ftrace too.
> 
> /sys/kernel/tracing # grep ^c_start available_filter_functions
> c_start.llvm.8011538628216713357
> c_start
> c_start.llvm.17132674095431275852
> 
> Tested-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> for this series.
> 
>> Changes v2 => v3:
>> 1. Remove the _without_suffix APIs, as kprobe will not use them.
>>   (Masami Hiramatsu)
>> 
>> v2: https://lore.kernel.org/live-patching/20240802210836.2210140-1-song@kernel.org/T/#u
>> 
>> Changes v1 => v2:
>> 1. Update the APIs to remove all .XXX suffixes (v1 only removes .llvm.*).
>> 2. Rename the APIs as *_without_suffix. (Masami Hiramatsu)
>> 3. Fix another user from kprobe. (Masami Hiramatsu)
>> 4. Add tests for the new APIs in kallsyms_selftests.
>> 
>> v1: https://lore.kernel.org/live-patching/20240730005433.3559731-1-song@kernel.org/T/#u
>> 
>> Song Liu (2):
>>  kallsyms: Do not cleanup .llvm.<hash> suffix before sorting symbols
>>  kallsyms: Match symbols exactly with CONFIG_LTO_CLANG
>> 
>> kernel/kallsyms.c          | 55 +++++---------------------------------
>> kernel/kallsyms_selftest.c | 22 +--------------
>> scripts/kallsyms.c         | 31 ++-------------------
>> scripts/link-vmlinux.sh    |  4 ---
>> 4 files changed, 9 insertions(+), 103 deletions(-)
>> 
>> --
>> 2.43.5
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>