On Fri, Oct 16, 2020 at 11:38:37PM +0200, Jiri Olsa wrote:
> On Wed, Sep 16, 2020 at 11:06:27AM +0200, Jiri Olsa wrote:
> > On Tue, Sep 15, 2020 at 02:17:46PM +0200, Jiri Olsa wrote:
> >
> > SNIP
> >
> > > <2><140d7aa>: Abbrev Number: 3 (DW_TAG_formal_parameter)
> > > <140d7ab> DW_AT_type : <0x140cfb6>
> > > <2><140d7af>: Abbrev Number: 3 (DW_TAG_formal_parameter)
> > > <140d7b0> DW_AT_type : <0x1406176>
> > > <2><140d7b4>: Abbrev Number: 3 (DW_TAG_formal_parameter)
> > > <140d7b5> DW_AT_type : <0x14060c9>
> > > <2><140d7b9>: Abbrev Number: 0
> > >
> > > the latter is just declaration.. but it's missing the
> > > <365d69d> DW_AT_declaration : 1
> > >
> > > so it goes through pahole's function processing:
> > >
> > > cu__encode_btf:
> > > ...
> > > cu__for_each_function(cu, core_id, fn) {
> > > int btf_fnproto_id, btf_fn_id;
> > >
> > > if (fn->declaration || !fn->external)
> > > continue;
> > > ...
> > >
> > >
> > > CC-ing Frank.. any idea why is the DW_AT_declaration : 1 missing?
> >
> > looks like gcc issue:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060
> >
> > let's see ;-)
>
> so this gcc bug did not disappear and the fix might be delayed,
> as I was told it's real complex and difficult to fix
>
> and it's no longer just rawhide issue, because I just started to
> see it in Fedora 32 after updating to gcc (GCC) 10.2.1 20201005
> (Red Hat 10.2.1-5)
>
> I'm checking on pahole's workaround, but so far I can't see dwarf
> based solution for that.. any thoughts/ideas? ;-)
hi,
FYI there's still no solution yet, so far the progress is:
the proposed workaround was to use the negation -> we don't have
DW_AT_declaration tag, so let's find out instead which DW_TAG_subprogram
tags have attached code and skip them if they don't have any:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060#c10
the attached patch is doing that, but the resulting BTF is missing
several functions due to another bug in dwarf:
https://bugzilla.redhat.com/show_bug.cgi?id=1890107
the only other workaround I can think of is to check each DW_TAG_subprogram
tag name with vmlinux symbol to ensure it's actually present,
I'll check on it, because as Mark suggested it might be good
for future not to completely rely on dwarf being correct, even
if that gcc bug gets eventually fixed
jirka
---
diff --git a/btf_encoder.c b/btf_encoder.c
index e90150784282..51a370d580b7 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -302,8 +302,9 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
cu__for_each_function(cu, core_id, fn) {
int btf_fnproto_id, btf_fn_id;
+ bool has_pc = !!function__addr(fn) || fn->ranges;
- if (fn->declaration || !fn->external)
+ if (!has_pc || !fn->external)
continue;
btf_fnproto_id = btf_elf__add_func_proto(btfe, &fn->proto, type_id_off);
diff --git a/dwarf_loader.c b/dwarf_loader.c
index d3586aa5b0dd..4763b9118475 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -953,6 +953,7 @@ static struct function *function__new(Dwarf_Die *die, struct cu *cu)
func->declaration = dwarf_hasattr(die, DW_AT_declaration);
func->external = dwarf_hasattr(die, DW_AT_external);
func->abstract_origin = dwarf_hasattr(die, DW_AT_abstract_origin);
+ func->ranges = dwarf_hasattr(die, DW_AT_ranges);
dwarf_tag__set_spec(func->proto.tag.priv,
attr_type(die, DW_AT_specification));
func->accessibility = attr_numeric(die, DW_AT_accessibility);
@@ -2023,8 +2024,10 @@ static int tag__recode_dwarf_type(struct tag *tag, struct cu *cu)
dtype = dwarf_cu__find_tag_by_ref(cu->priv, &dtag->abstract_origin);
if (dtype == NULL)
dtype = dwarf_cu__find_tag_by_ref(cu->priv, &specification);
- if (dtype != NULL)
+ if (dtype != NULL) {
fn->name = tag__function(dtype->tag)->name;
+ fn->external = tag__function(dtype->tag)->external;
+ }
else {
fprintf(stderr,
"%s: couldn't find name for "
diff --git a/dwarves.h b/dwarves.h
index 7c4254eded1f..3204f69abfe5 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -813,6 +813,7 @@ struct function {
uint8_t virtuality:2; /* DW_VIRTUALITY_{none,virtual,pure_virtual} */
uint8_t declaration:1;
uint8_t btf:1;
+ uint8_t ranges:1;
int32_t vtable_entry;
struct list_head vtable_node;
/* fields used by tools */
