I have created the appropriate issues in case anyone is interested:
clang not generating stack-passed parameters:
https://github.com/llvm/llvm-project/issues/94986
clang skipping and intermingling parameters:
https://github.com/llvm/llvm-project/issues/95645
GCC not generating stack-passed parameters:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115543
On Jun 14, 2024 at 9:37 PM +0300, Robinson, Paul ,
wrote:
> The spec does say they occur in the same order, which strongly implies that
> there is a DW_TAG_call_site_parameter for each actual parameter. Although,
> now that I say that, I have a memory of some discussion where a parameter
> entry might be omitted entirely. I don’t remember the details, but Jakub
> probably does. The spec does not clearly say that parameter entries can be
> omitted, though.
> --paulr
>
> From: Sergey
> Sent: Friday, June 14, 2024 1:12 PM
> To: dwarf-discuss@lists.dwarfstd.org; Robinson, Paul
> Subject: RE: [Dwarf-discuss] Request for clarification of handling
> stack-passed parameters
>
> In that case I shall create appropriate issues for the mentioned compilers in
> order to discuss the matter with them.
>
> I think I have found another issue with clang. In some cases it does not
> generate middle parameters: namely, it skipped the 2nd one yet included the
> 3rd one.
> It believe it does not match the standard (p91 line 6-7): "Call site
> parameter entries occur in the same order as the corresponding parameters in
> the source.", does it?
> On Jun 14, 2024, 15:11 +0300, Robinson, Paul , wrote:
>
> > I believe this is an issue with the implementations, although it is a bit
> > odd that both gcc and clang behave the same way. There should be a
> > DW_TAG_call_site_parameter for each parameter. DW_AT_location should
> > describe the stack slot where the parameter is passed. It should not be a
> > problem for the compiler to do that, the location description would be
> > evaluated in the context of the caller.
> > --paulr
> >
> > From: Dwarf-discuss
> > On Behalf
> > Of Sergey via Dwarf-discuss
> > Sent: Wednesday, June 12, 2024 9:57 AM
> > To: dwarf-discuss@lists.dwarfstd.org
> > Subject: [Dwarf-discuss] Request for clarification of handling stack-passed
> > parameters
> >
> > # Request for clarification of handling stack-passed parameters
> >
> > ## Background
> >
> > I came across this while parsing parameters of a variadic function in C.
> > Formal parameters are not sufficient for my case, since all the variadic
> > arguments are described with a single `DW_TAG_unspecified_parameters`,
> > whereas reading `DW_TAG_call_site_parameter` allows to get their locations
> > and values.
> >
> > ## Overview
> >
> > When generating a DWARF5 of a C function with **more than 6** parameters,
> > the generated `DW_TAG_call_site` contains only **first 6**
> > `DW_TAG_call_site_parameter`s (function's `DW_TAG_formal_parameter`s
> > contain all of them).
> >
> > Something I have noticed is that the parameters, which do not get
> > `DW_TAG_call_site_parameter` generated, are all **passed through
> > stack**(whereas first 6 through registers), as evident by function's
> > `DW_TAG_formal_parameter`'s `DW_AT_location` containing `DW_OP_fbreg`.
> >
> > ## Request for clarification
> >
> > It happens both with gcc and clang, however I was unable to find any
> > information in the standard regarding generation of only registed-passed
> > parameters.
> >
> > I request clarification on whether it is an issue with implementations, or
> > is there something in the standard which justifies the described behaviour.
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