r309386 - Recommit r308327 3rd time: Add a warning for missing

[Alex L via cfe-commits]

That's an interesting case. I'll tweak the warning to diagnose this
scenario better today.

On 29 July 2017 at 00:56, Hans Wennborg <hans at chromium.org> wrote:

> On Fri, Jul 28, 2017 at 7:41 AM, Alex Lorenz via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
> > Author: arphaman
> > Date: Fri Jul 28 07:41:21 2017
> > New Revision: 309386
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=309386&view=rev
> > Log:
> > Recommit r308327 3rd time: Add a warning for missing
> > '#pragma pack (pop)' and suspicious uses of '#pragma pack' in included
> files
> >
> > The second recommit (r309106) was reverted because the "non-default
> #pragma
> > pack value chages the alignment of struct or union members in the
> included file"
> > warning proved to be too aggressive for external projects like Chromium
> > (https://bugs.chromium.org/p/chromium/issues/detail?id=749197). This
> recommit
> > makes the problematic warning a non-default one, and gives it the
> > -Wpragma-pack-suspicious-include warning option.
> >
> > 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 did get warnings with this version too, but this time it looks like
> a real bug :-)
>
> C:\b\c\builder\ClangToTWin_dll_\src\third_party\usrsctp\
> usrsctplib\usrsctplib\netinet\sctp.h(51,9):
>  error: unterminated '#pragma pack (push, ...)' at end of file
> [-Werror,-Wpragma-pack]
>
> The interesting thing is that the file does reset the alignment, but
> it does it with a "#pragma pack()" which doesn't pop the stack, but
> just resets to the default value.
>
> It might be worth tweaking the warning to give a better message for
> this. A "#pragma pack(push, ..)" followed by "#pragma pack()" seems
> pretty dodgy since there's no point in pushing if the code isn't going
> to pop.
>
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