On Fri, Nov 13, 2020 at 7:13 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> 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.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
I tested locally, all seems to work fine. Left few suggestions below,
but those could be done in follow ups (or argued to not be done).
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
BTW, for some stats.
BEFORE allowing static funcs:
.BTF ELF section
=======================================
Data size: 4101624
Header size: 24
Types size: 2472836
Strings size: 1628764
BTF types
=======================================
Total 2472836 bytes (83310 types)
Struct: 920436 bytes (10305 types)
FuncProto: 638668 bytes (18869 types)
Func: 308304 bytes (25692 types)
Enum: 184308 bytes (2293 types)
Ptr: 173484 bytes (14457 types)
Array: 89064 bytes (3711 types)
Union: 81552 bytes (1961 types)
Const: 34368 bytes (2864 types)
Typedef: 32124 bytes (2677 types)
Var: 4688 bytes (293 types)
Datasec: 3528 bytes (1 types)
Fwd: 1656 bytes (138 types)
Volatile: 360 bytes (30 types)
Int: 272 bytes (17 types)
Restrict: 24 bytes (2 types)
AFTER allowing static funcs:
.BTF ELF section
=======================================
Data size: 4930558
Header size: 24
Types size: 2914016
Strings size: 2016518
BTF types
=======================================
Total 2914016 bytes (108282 types)
Struct: 920436 bytes (10305 types)
FuncProto: 851528 bytes (24814 types)
Func: 536664 bytes (44722 types)
Enum: 184308 bytes (2293 types)
Ptr: 173484 bytes (14457 types)
Array: 89064 bytes (3711 types)
Union: 81552 bytes (1961 types)
Const: 34368 bytes (2864 types)
Typedef: 32124 bytes (2677 types)
Var: 4688 bytes (293 types)
Datasec: 3528 bytes (1 types)
Fwd: 1656 bytes (138 types)
Volatile: 360 bytes (30 types)
Int: 256 bytes (16 types)
So 25692 vs 44722 functions, but the increase in func_proto is smaller
due to dedup. Good chunk is strings data for all those function and
parameter names.
> 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)))
Seeing Arnaldo's confusion, I remember initially I was similarly
confused. I think this p->generated = true should be moved out of
should_generate_function() and done here explicitly. Let's turn
should_generate_function() into find_allowed_function() or something,
to encapsulate bsearch. Checking !p || p->generated could be done here
explicitly.
> continue;
> } else {
> - if (fn->declaration || !fn->external)
> + if (!fn->external)
Hm.. why didn't you drop this fallback? For non-vmlinux, do you think
it's a problem to generate all FUNCs? Mostly theoretical question,
though.
> continue;
> }
>
> --
> 2.26.2
>
