On Fri 2023-06-02 16:24:01, Song Liu wrote:
> With CONFIG_LTO_CLANG, kallsyms.c:cleanup_symbol_name() removes symbols
> suffixes during comparison. This is problematic for livepatch, as
> kallsyms_on_each_match_symbol may find multiple matches for the same
> symbol, and fail with:
>
> livepatch: unresolvable ambiguity for symbol 'xxx' in object 'yyy'
>
> Fix this by using kallsyms_on_each_symbol instead, and matching symbols
> exactly.
>
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -166,7 +159,7 @@ static int klp_find_object_symbol(const char *objname, const char *name,
> if (objname)
> module_kallsyms_on_each_symbol(objname, klp_find_callback, &args);
> else
> - kallsyms_on_each_match_symbol(klp_match_callback, name, &args);
> + kallsyms_on_each_symbol(klp_find_callback, &args);
AFAIK, you have put a lot of effort to optimize the search recently.
The speedup was amazing, see commit 4dc533e0f2c04174e1ae
("kallsyms: Add helper kallsyms_on_each_match_symbol()").
Do we really need to waste this effort completely?
What about creating variants:
+ kallsyms_on_each_match_exact_symbol()
+ kallsyms_lookup_exact_names()
+ compare_exact_symbol_name()
Where compare_exact_symbol_name() would not try comparing with
cleanup_symbol_name()?
>
> /*
> * Ensure an address was found. If sympos is 0, ensure symbol is unique;
Otherwise, the patch looks fine. It is acceptable for me. I just want
to be sure that we considered the above alternative solution.
Best Regards,
Petr
