linux-kernel - Re: [PATCH] kallsyms: remove unused arch_get

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Message-ID: <ZG2bfsr+LwrxqsUX@bombadil.infradead.org>
Date:   Tue, 23 May 2023 22:07:10 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>, Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>
Cc:     linux-modules@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kallsyms: remove unused arch_get_kallsym() helper

On Wed, May 17, 2023 at 03:18:07PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The arch_get_kallsym() function was introduced so that x86 could override
> it, but that override was removed in bf904d2762ee ("x86/pti/64: Remove
> the SYSCALL64 entry trampoline"), so now this does nothing except causing
> a warning about a missing prototype:
> 
> kernel/kallsyms.c:662:12: error: no previous prototype for 'arch_get_kallsym' [-Werror=missing-prototypes]
>   662 | int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
> 
> Restore the old behavior before d83212d5dd67 ("kallsyms, x86: Export
> addresses of PTI entry trampolines") to simplify the code and avoid
> the warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Shouldn't this go through x86 as this sort of fixesss commit
bf904d2762ee ("x86/pti/64: Remove the SYSCALL64 entry trampoline")?

  Luis
> ---
>  kernel/kallsyms.c | 28 +---------------------------
>  1 file changed, 1 insertion(+), 27 deletions(-)
> 
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index e01c435595f9..dac13659601f 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -646,7 +646,6 @@ int sprint_backtrace_build_id(char *buffer, unsigned long address)
>  /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
>  struct kallsym_iter {
>  	loff_t pos;
> -	loff_t pos_arch_end;
>  	loff_t pos_mod_end;
>  	loff_t pos_ftrace_mod_end;
>  	loff_t pos_bpf_end;
> @@ -659,29 +658,9 @@ struct kallsym_iter {
>  	int show_value;
>  };
>  
> -int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
> -			    char *type, char *name)
> -{
> -	return -EINVAL;
> -}
> -
> -static int get_ksymbol_arch(struct kallsym_iter *iter)
> -{
> -	int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
> -				   &iter->value, &iter->type,
> -				   iter->name);
> -
> -	if (ret < 0) {
> -		iter->pos_arch_end = iter->pos;
> -		return 0;
> -	}
> -
> -	return 1;
> -}
> -
>  static int get_ksymbol_mod(struct kallsym_iter *iter)
>  {
> -	int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
> +	int ret = module_get_kallsym(iter->pos - kallsyms_num_syms,
>  				     &iter->value, &iter->type,
>  				     iter->name, iter->module_name,
>  				     &iter->exported);
> @@ -764,7 +743,6 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
>  	iter->nameoff = get_symbol_offset(new_pos);
>  	iter->pos = new_pos;
>  	if (new_pos == 0) {
> -		iter->pos_arch_end = 0;
>  		iter->pos_mod_end = 0;
>  		iter->pos_ftrace_mod_end = 0;
>  		iter->pos_bpf_end = 0;
> @@ -780,10 +758,6 @@ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
>  {
>  	iter->pos = pos;
>  
> -	if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
> -	    get_ksymbol_arch(iter))
> -		return 1;
> -
>  	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
>  	    get_ksymbol_mod(iter))
>  		return 1;
> -- 
> 2.39.2
>