Re: [PATCH 2/2] btf_encoder: Fix function generation

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Nov 13, 2020 at 04:12:22PM +0100, Jiri Olsa escreveu:
> Current conditions for picking up function records break
> BTF data on some gcc versions.
> 
> Some function records can appear with no arguments but with
> declaration tag set, so moving the 'fn->declaration' in front
> of other checks.
> 
> Then checking if argument names are present and finally checking
> ftrace filter if it's present. If ftrace filter is not available,
> using the external tag to filter out non external functions.

Humm has_arg_names() will return true for a:

void foo(void)

function, which I think is right, but can't this function appear
multiple times in different CUs and we end up with the same function
multiple times in the BTF info?

- Arnaldo
 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  btf_encoder.c | 24 ++++++++++--------------
>  1 file changed, 10 insertions(+), 14 deletions(-)
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index d531651b1e9e..de471bc754b1 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -612,25 +612,21 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
>  		const char *name;
>  
>  		/*
> -		 * The functions_cnt != 0 means we parsed all necessary
> -		 * kernel symbols and we are using ftrace location filter
> -		 * for functions. If it's not available keep the current
> -		 * dwarf declaration check.
> +		 * Skip functions that:
> +		 *   - are marked as declarations
> +		 *   - do not have full argument names
> +		 *   - are not in ftrace list (if it's available)
> +		 *   - are not external (in case ftrace filter is not available)
>  		 */
> +		if (fn->declaration)
> +			continue;
> +		if (!has_arg_names(cu, &fn->proto))
> +			continue;
>  		if (functions_cnt) {
> -			/*
> -			 * We check following conditions:
> -			 *   - argument names are defined
> -			 *   - there's symbol and address defined for the function
> -			 *   - function address belongs to ftrace locations
> -			 *   - function is generated only once
> -			 */
> -			if (!has_arg_names(cu, &fn->proto))
> -				continue;
>  			if (!should_generate_function(btfe, function__name(fn, cu)))
>  				continue;
>  		} else {
> -			if (fn->declaration || !fn->external)
> +			if (!fn->external)
>  				continue;
>  		}
>  
> -- 
> 2.26.2
> 

-- 

- Arnaldo