Re: [PATCH v3 0/2] Fix kallsyms with CONFIG_LTO_CLANG

From: Song Liu
Date: Tue Aug 13 2024 - 17:21:32 EST


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@xxxxxxxxxx> wrote:
>
> On Wed, 7 Aug 2024 15:05:11 -0700
> Song Liu <song@xxxxxxxxxx> 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@xxxxxxxxxx>
> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
>
> 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@xxxxxxxxxx/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@xxxxxxxxxx/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@xxxxxxxxxx>