Re: [PATCH] perf probe: Add support for DW_OP_call_frame_cfa vars

[Masami Hiramatsu <mhiramat@kernel.org>]

Hi Daniel,

On Wed,  1 Apr 2020 19:19:52 +0300
Daniel Shaulov <daniel.shaulov@gmail.com> wrote:

> Add support for probes on variables with DW_OP_call_frame_cfa
> as the dwarf operation in the debug info.
> 
> Some compilers (specifically Golang compiler) output
> DW_OP_call_frame_cfa instead of DW_OP_fbreg for variables
> on the stack. If DW_OP_call_frame_cfa is the only expression
> than it is the same as DW_OP_fbreg with an offset of zero.
> In the case of the Golang compiler, DW_OP_call_frame_cfa may
> be followed by DW_OP_consts, with a number and than DW_OP_plus.
> This trio is the same as DW_OP_fbreg with the number from
> DW_OP_consts as the offset.
> 
> With this change, probing on functions in Golang with variables works.
> 

This looks good to me:)

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks!

> Signed-off-by: Daniel Shaulov <daniel.shaulov@granulate.io>
> ---
>  tools/perf/util/probe-finder.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index e4cff49384f4..866b17aea263 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -240,11 +240,23 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
>  	}
>  
>  	/* If this is based on frame buffer, set the offset */
> -	if (op->atom == DW_OP_fbreg) {
> +	if (op->atom == DW_OP_fbreg || op->atom == DW_OP_call_frame_cfa) {
>  		if (fb_ops == NULL)
>  			return -ENOTSUP;
>  		ref = true;
> -		offs = op->number;
> +		if (op->atom == DW_OP_fbreg) {
> +			offs = op->number;
> +		} else if (nops == 3) {
> +			/*
> +			 * In the case of DW_OP_call_frame_cfa, we either have
> +			 * an offset of 0 or we have two more expressions that
> +			 * add a const
> +			 */
> +			if ((op + 1)->atom != DW_OP_consts ||
> +			    (op + 2)->atom != DW_OP_plus)
> +				return -ENOTSUP;
> +			offs = (op + 1)->number;
> +		}
>  		op = &fb_ops[0];
>  	}
>  
> -- 
> 2.22.0
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>