llvm dev - Dec 2013 - [LLVMdev] Switching to the new MingW ABI

The tool uses Clang to parse the user's C/C++ code to get the calling
conventions from the AST, so they need to match the ones in the compiled
libraries to allow correct interop. If the user libraries were compiled
with GCC 4.6 (which stills seems used by some MinGW distros) then once we
upgrade to the latest Clang we'll start getting thiscall CC instead of the
correct one used pre-4.7 for those libraries. If there was something like
an "-fgcc-abi=4.6" flag we could pass to Clang, then it would provide
us
with the correct CCs for the given GCC version.

If the community thinks that is undesirable for the project then we can
work around it on our side, but it seems to me these details should be
contained in Clang.


On Tue, Dec 10, 2013 at 2:21 PM, Rafael Espíndola <
rafael.espindola at gmail.com> wrote:
> On 10 December 2013 09:16, João Matos <ripzonetriton at gmail.com>
wrote:
> > For the current project I'm working on
(https://github.com/mono/CppSharp
> )
> > having the flags to change the ABI based on a GCC version would be
> ideal. If
> > there are no flags, this means we must implement some logic to change
the
> > calling conventions of methods manually to how they were pre-4.7.
Should
> not
> > be a lot of work but it'd be best to contain all the C++ ABI
details
> inside
> > Clang itself.
>
> Because you must link with gcc 4.6 compiled libraries for now or is
> that a permanent thing?
>
> Cheers,
> Rafael
>


-- 
João Matos
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On 10 December 2013 11:18, João Matos <ripzonetriton at gmail.com>
wrote:
> The tool uses Clang to parse the user's C/C++ code to get the calling
> conventions from the AST, so they need to match the ones in the compiled
> libraries to allow correct interop. If the user libraries were compiled
with
> GCC 4.6 (which stills seems used by some MinGW distros)
Do you have an idea for how long you will have to support these
distros? This change would only show up on clang 3.5, and it is not
even expected to build with gcc 4.6
> then once we upgrade
> to the latest Clang we'll start getting thiscall CC instead of the
correct
> one used pre-4.7 for those libraries. If there was something like an
> "-fgcc-abi=4.6" flag we could pass to Clang, then it would
provide us with
> the correct CCs for the given GCC version.
>
> If the community thinks that is undesirable for the project then we can
work
> around it on our side, but it seems to me these details should be contained
> in Clang.
On the clang side the change should be trivial (note the attached
clang.patch on first email). Do you think that is something you can
keep locally if needed?

If we can avoid creating new ABI options I think that is desirable.

Cheers,
Rafael

>
> On the clang side the change should be trivial (note the attached
>  clang.patch on first email). Do you think that is something you can
> keep locally if needed?
>
> If we can avoid creating new ABI options I think that is desirable.
>
I can work around it locally, let's keep it simple on the Clang side.



-- 
João Matos
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