Re: [PATCH] kallsyms: work around bogus -Wrestrict warning

[Masami Hiramatsu <mhiramat@kernel.org>]

Hi Arnd,

On Tue,  7 Jan 2020 22:40:26 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> gcc -O3 produces some really odd warnings for this file:
> 
> kernel/kallsyms.c: In function 'sprint_symbol':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> kernel/kallsyms.c: In function 'sprint_symbol_no_offset':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> kernel/kallsyms.c: In function 'sprint_backtrace':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> 
> This obviously cannot be since it is preceded by an 'if (name != buffer)'
> check.

Hmm, this looks like a bug in gcc.

> 
> Using sprintf() instead of strcpy() is a bit wasteful but is
> the best workaround I could come up with.
> 
> Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  kernel/kallsyms.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index d812b90f4c86..726b8eeb223e 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -366,7 +366,7 @@ static int __sprint_symbol(char *buffer, unsigned long address,
>  		return sprintf(buffer, "0x%lx", address - symbol_offset);
>  
>  	if (name != buffer)
> -		strcpy(buffer, name);
> +		sprintf(buffer, "%s", name);

BTW, this seems not happen. kallsyms_lookup() (and it's subfunctions)
always stores the result into buffer unless name == NULL.
Maybe we can remove these 2 lines?
(and add a comment line for kallsyms_lookup() so that it guarantees the
 symbol name always stored in namebuf argument)

Thank you,


-- 
Masami Hiramatsu <mhiramat@kernel.org>