On Thu, Jul 27, 2017 at 3:41 AM, Alex L <arpha...@gmail.com> wrote: > > > On 26 July 2017 at 22:32, Hans Wennborg <h...@chromium.org> wrote: >> >> On Wed, Jul 26, 2017 at 11:27 AM, Hans Wennborg <h...@chromium.org> wrote: >> > On Wed, Jul 26, 2017 at 5:20 AM, Alex Lorenz via cfe-commits >> > <cfe-commits@lists.llvm.org> wrote: >> >> Author: arphaman >> >> Date: Wed Jul 26 05:20:57 2017 >> >> New Revision: 309106 >> >> >> >> URL: http://llvm.org/viewvc/llvm-project?rev=309106&view=rev >> >> Log: >> >> Recommit r308327 2nd time: Add a warning for missing >> >> '#pragma pack (pop)' and suspicious uses of '#pragma pack' in included >> >> files >> >> >> >> The first recommit (r308441) caused a "non-default #pragma pack value >> >> might >> >> change the alignment of struct or union members in the included file" >> >> warning >> >> in LLVM itself. This recommit tweaks the added warning to avoid >> >> warnings for >> >> #includes that don't have any records that are affected by the >> >> non-default >> >> alignment. This tweak avoids the previously emitted warning in LLVM. >> >> >> >> Original message: >> >> >> >> This commit adds a new -Wpragma-pack warning. It warns in the following >> >> cases: >> >> >> >> - When a translation unit is missing terminating #pragma pack (pop) >> >> directives. >> >> - When entering an included file if the current alignment value as >> >> determined >> >> by '#pragma pack' directives is different from the default alignment >> >> value. >> >> - When leaving an included file that changed the state of the current >> >> alignment >> >> value. >> >> >> >> rdar://10184173 >> >> >> >> Differential Revision: https://reviews.llvm.org/D35484 >> > >> > We have code in Chromium that does exactly this: >> > >> > gles2_cmd_format.h does #pragma pack(push, 4) and then #includes a >> > file with some generated structs, with the intention that the pragma >> > applies to them. >> > >> > What's the best way to pacify the warning in this case? >> > >> > (We're tracking this in >> > https://bugs.chromium.org/p/chromium/issues/detail?id=749197) >> >> I agree that cases 1) and 3) from your patch description make sense to >> warn for, but I'm not sure that's the case for 2). Do you have >> examples where this catches any bugs? In our case #pragma packing an >> included file is intentional, and I suspect it might be a bit of a >> pattern. > > > I see, thanks for your input. > > 2) is generally designed for times when #pragma pack pop was accidentally > used too late (after some #includes that unintentionally receive the > alignment). I can see how some projects use this pattern heavily, and I > don't think there's a good way to pacify this warning in that case. > > I think that for us it would be reasonable to turn 2) off by default, and > allow users to enable it explicitly using a stronger flag (something like > -Wpragma-pack-suspicious-include?). I think that I will leave 2) out of this > commit, recommit it without 2) and then commit 2) as a non-default warning > that uses a separate flag.
That sounds reasonable. You can probably still do it with the same commit, just moving 2) behind a separate flag. Thanks, Hans _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits