linux-kernel - Re: [PATCH v10 04/27] kallsyms: support "big" kernel symbols

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Date:   Sat, 29 Oct 2022 10:41:47 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, patches@...ts.linux.dev,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Gary Guo <gary@...yguo.net>, Boqun Feng <boqun.feng@...il.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v10 04/27] kallsyms: support "big" kernel symbols

On Tue, Sep 27, 2022 at 03:14:35PM +0200, Miguel Ojeda wrote:
> Rust symbols can become quite long due to namespacing introduced
> by modules, types, traits, generics, etc.
> 
> Increasing to 255 is not enough in some cases, therefore
> introduce longer lengths to the symbol table.
> 
> In order to avoid increasing all lengths to 2 bytes (since most
> of them are small, including many Rust ones), use ULEB128 to
> keep smaller symbols in 1 byte, with the rest in 2 bytes.
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>
> 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>
> Co-developed-by: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  kernel/kallsyms.c  | 26 ++++++++++++++++++++++----
>  scripts/kallsyms.c | 29 ++++++++++++++++++++++++++---
>  2 files changed, 48 insertions(+), 7 deletions(-)
> 

This patch results in the following spurious build error.

Building powerpc:allnoconfig ... failed
--------------
Error log:
Inconsistent kallsyms data
Try make KALLSYMS_EXTRA_PASS=1 as a workaround

Symbol file differences:
10c10
< 00009720 g       .rodata	00000000 kallsyms_relative_base
---
> 0000971c g       .rodata	00000000 kallsyms_relative_base
12,16c12,16
< 00009724 g       .rodata	00000000 kallsyms_num_syms
< 00009728 g       .rodata	00000000 kallsyms_names
< 00022628 g       .rodata	00000000 kallsyms_markers
< 000226c0 g       .rodata	00000000 kallsyms_token_table
< 00022a2c g       .rodata	00000000 kallsyms_token_index
---
> 00009720 g       .rodata	00000000 kallsyms_num_syms
> 00009724 g       .rodata	00000000 kallsyms_names
> 00022618 g       .rodata	00000000 kallsyms_markers
> 000226b0 g       .rodata	00000000 kallsyms_token_table
> 00022a1c g       .rodata	00000000 kallsyms_token_index

This is the only difference. There are no additional symbols.

Reverting this patch fixes the problem.

Guenter