Re: [PATCH v5 2/3] perf dwarf-aux: Add C++ vtable helpers

[sashiko-bot@kernel.org]

> Add DWARF helper functions needed to resolve C++ virtual function calls
> statically in the data type profiling:
> 
> - die_get_vtable_index() returns the vtable slot index of a virtual
>   function DIE from DW_AT_vtable_elem_location.  DWARF defines the
>   attribute as a location description of the slot but GCC and Clang
>   both emit the slot index as a single DW_OP_constu, which is also how
>   debuggers interpret it.
> 
> - die_find_virtual_func() finds the virtual function DIE at a given
>   vtable slot index of a class.  The (primary) vtable of a class starts
>   with the vtable of its primary base class, i.e. the first non-virtual
>   base class at offset 0 which has a vtable, and the slots for virtual
>   functions introduced by the class come after that.  So it looks at
>   the class first and then follows the primary base class chain.
> [ ... ]
> finds Base::set() through the primary base.  The vtable pointer at
> offset 16 belongs to the Other subobject, so it's looked up with Other
> where slot 0 finds Other::hi().
> 
> Signed-off-by: Yanbo Zhao <yzhao62@ncsu.edu>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261105181949.43198-1-yzhao62@ncsu.edu?part=2