[cfe-dev] Force __builtin_va_list to be a char* in any architecture?

[Oliver Stannard via cfe-dev]

Hi Mikhail,

I'm not aware of any option to do that, and I don't think such an option
could work for AArch64 without completely changing the ABI. For
AArch64, __builtin_va_list is a struct with 5 members, which is needed
because arguments can be passed in a mixture of integer and floating-point
registers, and on the stack, so a single pointer can't store all of the
necessary state.

Oliver

On Thu, 12 Dec 2019 at 17:14, Mikhail Ramalho via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi all,
>
> Is there any way to force __builtin_va_list to always be a char*,
> regardless of the architecture?
>
> We are using clang as a frontend in our project and our analysis relies on
> the fact that __builtin_va_list is a char* on 64 bits architecture as well,
> but we keep getting:
>
> |-TypedefDecl 0x4148c78 <<invalid sloc>> <invalid sloc> implicit
> referenced __builtin_va_list 'struct __va_list_tag [1]'
> | `-ConstantArrayType 0x4148c20 'struct __va_list_tag [1]' 1
> |   `-RecordType 0x4148aa0 'struct __va_list_tag'
> |     `-Record 0x4148a10 '__va_list_tag'
>
> I've tried several different combinations of defines but to no avail.
>
> In case it is not possible, we could submit a patch to add an option to
> force that on clang. A bit of an overkill given that we would be the only
> users (I think).
>
> Best,
>
> --
>
> Mikhail Ramalho.
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> cfe-dev at lists.llvm.org
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>
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