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From: "mity at morous dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/64384] New: mingw-w64: stdcall function returning an aggregate is incompatible with MS ABI
Date: Tue, 23 Dec 2014 13:39:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64384

            Bug ID: 64384
           Summary: mingw-w64: stdcall function returning an aggregate is
                    incompatible with MS ABI
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mity at morous dot org

When using COM interface (i.e. calling stdcall function/method), aggregates are
returned through an implicit parameter after the this/interface pointer,
according to MS ABI. However it is not so when using gcc.

This issue manifests itself when e.g. calling ID2D1RenderTarget::GetSize() from
<d2d1.h> as discussed here:

https://sourceforge.net/p/mingw-w64/mailman/mingw-w64-public/?style=threaded&viewmonth=201412&viewday=23


Wine team encountered the issue too, they seem to "solve" the issue on their
side by ugly hacks and changing prototypes of the relevant functions for now:

https://www.winehq.org/pipermail/wine-patches/2014-September/134351.html