Re: [PATCH v1] perf test type profiling: Remote typedef on struct

[Dmitry Dolgov]

> On Wed, Mar 04, 2026 at 11:44:16AM +0100, Dmitry Dolgov wrote:
> > On Mon, Mar 02, 2026 at 03:58:21PM -0800, Ian Rogers wrote:
> > The typedef creates an issue where the struct or the typedef may
> > appear in the output and cause the "perf data type profiling tests" to
> > fail. Let's remove the typedef to keep the test passing.
> 
> Yes, makes sense to me, thanks. As mentioned in the previous message, it
> sounds fishy to me that perf record and perf mem record capture
> different data type -- I'll try to get to the bottom of it.

I think I figured it out. To reiterate, the problem was that in my environment
this:

    $ perf record ...
    $ perf annotate --code-with-type ...

was showing a different data structure for workload_datasym_buf1 (buf vs struct
_buf) than:

    $ perf mem record ...
    $ perf annotate --code-with-type ...

It turns out that the type_die for this variable was derived differently: for
"record" it was going through check_variable, for "mem record" through
global_var__collect. If the type tag is DW_TAG_typedef, check_variable tries to
figure out a real data type via die_get_real_type, which says this:

    /**
     * [...]
     * If the type is qualifiers (e.g. const) or typedef, this skips it
     * and tries to find real type (structure or basic types, e.g. int).
     */

But the underlying implementation doesn't actually check for DW_TAG_typedef for
some reason:

	while (tag == DW_TAG_const_type ||
		 tag == DW_TAG_restrict_type ||
		 tag == DW_TAG_volatile_type ||
		 tag == DW_TAG_shared_type);

By itself it doesn't look problematic, but for some reason datasym test was
producing such a code, that had a chain of two DW_TAG_typedef in a row, so that
die_get_real_type was returning a DW_TAG_typedef again.

It looks to me like a deficiency of die_get_real_type, and the following code
change fixes the problem for me:

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 9267af204c7..de152fae1d9 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -279,6 +279,7 @@ Dwarf_Die *__die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
        } while (tag == DW_TAG_const_type ||
                 tag == DW_TAG_restrict_type ||
                 tag == DW_TAG_volatile_type ||
+                tag == DW_TAG_typedef ||
                 tag == DW_TAG_shared_type);

        return vr_die;

Does this change sound reasonable?