linux-kernel - Re: [PATCH v1 3/3] kallsyms: increase maximum kernel symbol length to 512

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Date:   Fri, 6 May 2022 10:34:58 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Helge Deller <deller@....de>,
        Stephen Boyd <swboyd@...omium.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Changbin Du <changbin.du@...el.com>,
        Nathan Chancellor <nathan@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        linux-perf-users@...r.kernel.org, rust-for-linux@...r.kernel.org,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Gary Guo <gary@...yguo.net>, Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v1 3/3] kallsyms: increase maximum kernel symbol length
 to 512

On Thu 2022-05-05 21:16:45, Miguel Ojeda wrote:
> Rust symbols can become quite long due to namespacing introduced
> by modules, types, traits, generics, etc. For instance,
> the following code:
> 
>     pub mod my_module {
>         pub struct MyType;
>         pub struct MyGenericType<T>(T);
> 
>         pub trait MyTrait {
>             fn my_method() -> u32;
>         }
> 
>         impl MyTrait for MyGenericType<MyType> {
>             fn my_method() -> u32 {
>                 42
>             }
>         }
>     }
> 
> generates a symbol of length 96 when using the upcoming v0 mangling scheme:
> 
>     _RNvXNtCshGpAVYOtgW1_7example9my_moduleINtB2_13MyGenericTypeNtB2_6MyTypeENtB2_7MyTrait9my_method
> 
> At the moment, Rust symbols may reach up to 300 in length.
> Setting 512 as the maximum seems like a reasonable choice to
> keep some headroom.
> 
> Co-developed-by: Alex Gaynor <alex.gaynor@...il.com>
> Signed-off-by: Alex Gaynor <alex.gaynor@...il.com>
> Co-developed-by: Wedson Almeida Filho <wedsonaf@...gle.com>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@...gle.com>
> Co-developed-by: Gary Guo <gary@...yguo.net>
> Signed-off-by: Gary Guo <gary@...yguo.net>
> Co-developed-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>

I was primary interested into the livepatching code.
But the entire patch looks good:

Reviewed-by: Petr Mladek <pmladek@...e.com>

I just hope that it will not cause stack overflows
somewhere.

Best Regards,
Petr