[Dwarf-discuss] Request for clarification of handling stack-passed parameters

[Sergey]

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 <paul.robinson@sony.com>, 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 <dwarf-discuss-bounces+paul.robinson=sony.com@lists.dwarfstd.org> 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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