Re: [PATCH] ftrace: shut up -Wcast-function-type warning for ftrace_ops_no_ops

From: Peter Zijlstra
Date: Tue Mar 23 2021 - 03:40:25 EST


On Mon, Mar 22, 2021 at 10:49:58PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> With 'make W=1', gcc warns about casts between incompatible function
> types:
>
> kernel/trace/ftrace.c:128:31: error: cast between incompatible function types from 'void (*)(long unsigned int, long unsigned int)' to 'void (*)(long unsigned int, long unsigned int, struct ftrace_ops *, struct ftrace_regs *)' [-Werror=cast-function-type]
> 128 | #define ftrace_ops_list_func ((ftrace_func_t)ftrace_ops_no_ops)
> | ^
>
> As the commet here explains, this one was intentional, so shut up the
> warning harder by using a double cast.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> kernel/trace/ftrace.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 4d8e35575549..d8fc87a17421 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -125,7 +125,7 @@ static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
> #else
> /* See comment below, where ftrace_ops_list_func is defined */
> static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip);
> -#define ftrace_ops_list_func ((ftrace_func_t)ftrace_ops_no_ops)
> +#define ftrace_ops_list_func ((ftrace_func_t)(void *)ftrace_ops_no_ops)

So now we're making perfectly fine code worse, because GCC is stupid?

Please just kill the warning, like we do with so many other warnings.
It's broken!