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Re: [SG12] EWG Requests feedback/suggestions on Core Issue 1555

From: Gabriel Dos Reis <gdr_at_[hidden]>
Date: Wed, 13 May 2020 20:11:08 +0000
I received the previous message like 1min before this one (although it was dared April 15 2020), so I don't know that was sufficient for the group to discuss :-)

-- Gaby
________________________________
From: SG12 <sg12-bounces_at_[hidden]> on behalf of Keane, Erich via SG12 <sg12_at_[hidden]>
Sent: Wednesday, April 22, 2020 8:34:11 AM
To: sg12_at_[hidden] <sg12_at_[hidden]>
Cc: Keane, Erich <erich.keane_at_[hidden]>
Subject: Re: [SG12] EWG Requests feedback/suggestions on Core Issue 1555


Hi all!

Did this make it to the mailing list? I didnít see any discussion on this so I didnít know if the group decided to just cover this in a telecon that I didnít hear about, or it just dropped ?? I just wanted to make sure it doesnít get dropped.



Thanks,
Erich



From: Keane, Erich
Sent: Wednesday, April 15, 2020 8:56 AM
To: sg12_at_[hidden]
Cc: JF Bastien <cxx_at_[hidden]>
Subject: EWG Requests feedback/suggestions on Core Issue 1555



Hi SG12-

In the EWG telecon today, we discussed core issue 1555 (http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_closed.html#1555<https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.open-std.org%2Fjtc1%2Fsc22%2Fwg21%2Fdocs%2Fcwg_closed.html%231555&data=02%7C01%7Cgdr%40microsoft.com%7C40c6746bc4a348e4c69508d7f7786aae%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637249968868887111&sdata=7bsDz0L7qhKojk8IjFyKggli2R1l4ib4cTiFjNmnopc%3D&reserved=0>). The summary of the issue is that the standard makes function types of different language linkage incompatible, thus calling a function from a pointer with different language linkage is undefined behavior. One unnamed implementation was referenced during the discussion where language linkage effects calling convention.



The major implementations (and none other than the 1 unnamed one listed) simply donít implement this restriction (that the types arenít compatible) because the calling convention is the same between the linkages.



EWG was undecided as to whether we should remove this instance restriction, or leave it as undefined behavior. None seemed to support CWG1555ís proposed resolution of conditionally-supported behavior.



(TL-DR people can start here?? )

The outcome of the discussion is that the impact and scope of this Undefined Behavior should be evaluated by SG12, and if possible, provide a set of recommendations for dealing with this core issue.



-Erich

Received on 2020-05-13 15:14:22