Re: [PATCH v5 3/3] perf annotate: Resolve C++ virtual function calls in x86 insn tracking

[sashiko-bot@kernel.org]

> A C++ virtual function call is an indirect call through the vtable.
> The instruction tracking of the data type profiling cannot resolve the
> callee name for it, so the return type is lost and the type of the
> register holding the returned value is unknown after the call.  It
> matters when the returned value is used directly to access memory, like
> in 'p->next()->val', where no DWARF variable describes the temporary.
> 
> The vtable pointer and the slot index are known statically from the
> type of the object pointer, so the callee can be found by DWARF.  Track
> the two steps of a virtual call in update_insn_state_x86():
> 
> 1. Loading the vtable pointer from the object.  When a load from a
>    register with a pointer type hits the '_vptr' member of the class
>    (or one of its base classes), the destination register is marked as
>    TSR_KIND_VTABLE_PTR with the class DIE returned by
> [ ... ]
>   1260:  addq  $1, %rbx
>   1264:  callq *%rax
>   1266:  addq  8(%rax), %r12     # data-type: struct Node +0x8 (val)
> 
> 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=3