linux-kernel - Re: [PATCH] init: keep boot_command

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Message-ID: <CAKwvOdnk+e_QmE+QpcqzntNVgf8mL+NOPtUggj4F__iTf_XD+A@mail.gmail.com>
Date:   Wed, 26 Jul 2023 09:25:39 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] init: keep boot_command_line after init

On Wed, Jul 26, 2023 at 7:33 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> The boot command line is not available after the init section gets discarded,
> so adding a permanent reference to it causes a link time warning:
>
> WARNING: modpost: vmlinux: section mismatch in reference: cmdline_load_proc_show+0x2 (section: .text) -> boot_command_line (section: .init.data)

cmdline_load_proc_show is probably inlined, but should it also be
marked __init?  It's lone call site seems to be __init AFAICT.

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ERROR: modpost: Section mismatches detected.
> Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
>
> Change it to __ro_after_init to prevent it from getting freed.
>
> Fixes: cf9eca90a3397 ("fs/proc: Add /proc/cmdline_load for boot loader arguments")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/linux/init.h | 2 +-
>  init/main.c          | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/init.h b/include/linux/init.h
> index 9a5973324072b..4e97a7a29a4d7 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -143,7 +143,7 @@ struct file_system_type;
>
>  /* Defined in init/main.c */
>  extern int do_one_initcall(initcall_t fn);
> -extern char __initdata boot_command_line[];
> +extern char boot_command_line[];
>  extern char *saved_command_line;
>  extern unsigned int saved_command_line_len;
>  extern unsigned int reset_devices;
> diff --git a/init/main.c b/init/main.c
> index c946ab87783a1..981170da0b1cd 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -135,7 +135,7 @@ EXPORT_SYMBOL(system_state);
>  void (*__initdata late_time_init)(void);
>
>  /* Untouched command line saved by arch-specific code. */
> -char __initdata boot_command_line[COMMAND_LINE_SIZE];
> +char boot_command_line[COMMAND_LINE_SIZE] __ro_after_init;
>  /* Untouched saved command line (eg. for /proc) */
>  char *saved_command_line __ro_after_init;
>  unsigned int saved_command_line_len __ro_after_init;
> --
> 2.39.2
>


-- 
Thanks,
~Nick Desaulniers