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SubjectRe: [PATCH] perf probe: Add support for DW_OP_call_frame_cfa vars
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>

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