On Thu, Dec 04, 2025 at 10:10:10AM -0800, Y Song wrote:
> > DW_OP_GNU_parameter_ref is an extension, see
> > https://dwarfstd.org/issues/230109.1.html
> > In any case, I don't see why you need something like
> > DW_TAG_inlined_subroutine at DW_TAG_compile_unit scope, you can't inline a
> > function into a translation unit.
>
> Thanks. This is indeed an option. See
> https://github.com/llvm/llvm-project/pull/157349#issuecomment-3412590751
> But lldb has some concerns since it change the *existing* output
> during lldb debugger.
> See the above link.
>
> Do you have better suggestions or have a way to make lldb people okay with it?
GCC has been emitting it this way for at least 15 years, so lldb better
handles it.
When you change signature of a function, it is no longer the original, it is
some modified copy (clone) of that, so that is how it should be represented.
Now, either you also emit the function with unchanged signature (e.g. if it
is not TU-local function but the compiler wants to optimize it anyway), or
don't. And, there doesn't need to be just one clone, there can be several,
e.g. several callers pass the same constant to one argument, so that argument
can be optimized away in the clone, but other callers pass constant to a
different
argument or the argument is needed by the callee or cloning can be done
based on interprocedural value range propagation etc.
Anyway, from what you've posted, i.e. that DW_OP_piece 8 DW_OP_reg rsi
DW_OP_piece 1
etc. you can see the first 8 bytes of the structure are <optimized out> and
in where is the last byte passed in. There are ways to get value also in
some cases from DW_TAG_call_site information if you can prove what the
caller is, but if it is not passed, it will be always a best effort,
sometimes there is no way to find out the argument value that wasn't passed.
Jakub
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