linux-kernel - Re: [PATCH 2/2] [v2] kallsyms: rework symbol lookup return codes

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Date:   Mon, 24 Jul 2023 12:28:50 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Palmer Dabbelt <palmer@...osinc.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-modules@...r.kernel.org
Subject: Re: [PATCH 2/2] [v2] kallsyms: rework symbol lookup return codes

On Mon, Jul 24, 2023 at 03:53:02PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Building with W=1 in some configurations produces a false positive
> warning for kallsyms:
> 
> kernel/kallsyms.c: In function '__sprint_symbol.isra':
> kernel/kallsyms.c:503:17: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>   503 |                 strcpy(buffer, name);
>       |                 ^~~~~~~~~~~~~~~~~~~~
> 
> This originally showed up while building with -O3, but later started
> happening in other configurations as well, depending on inlining
> decisions. The underlying issue is that the local 'name' variable is
> always initialized to the be the same as 'buffer' in the called functions
> that fill the buffer, which gcc notices while inlining, though it could
> see that the address check always skips the copy.
> 
> The calling conventions here are rather unusual, as all of the internal
> lookup functions (bpf_address_lookup, ftrace_mod_address_lookup,
> ftrace_func_address_lookup, module_address_lookup and
> kallsyms_lookup_buildid) already use the provided buffer and either return
> the address of that buffer to indicate success, or NULL for failure,
> but the callers are written to also expect an arbitrary other buffer
> to be returned.
> 
> Rework the calling conventions to return the length of the filled buffer
> instead of its address, which is simpler and easier to follow as well
> as avoiding the warning. Leave only the kallsyms_lookup() calling conventions
> unchanged, since that is called from 16 different functions and
> adapting this would be a much bigger change.
> 
> Link: https://lore.kernel.org/all/20200107214042.855757-1-arnd@arndb.de/
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

For modules side of things:

Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>

  Luis