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Date: Wed, 27 Oct 2021 23:06:54 +0900
Message-ID: <CAAr43iPPAMTUnJzOa=2B3R1Z84SWaDbrYEebLhqJDBnhn475UA@mail.gmail.com>
Subject: Re: gcc 11 weird bug
To: "cygwin@cygwin.com" <cygwin@cygwin.com>
From: Joel Rees via Cygwin <cygwin@cygwin.com>
Reply-To: Joel Rees <joel.rees@gmail.com>
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On Wed, Oct 27, 2021 at 7:56 PM Hannes Domani via Cygwin
<cygwin@cygwin.com> wrote:
>
>  Am Mittwoch, 27. Oktober 2021, 11:19:19 MESZ hat Thomas Wolff <towo@towo.net> Folgendes geschrieben:
>
> > I noticed that mintty did not compile anymore after upgrade to gcc 11,
> > but only on cygwin 32-bit.
> > I tried to minimize the test case as much as possible without having the
> > bug vanish, to the attached standalone file.
> > Compile this with
> > cc -O2 -Wall -Werror m0.c
> > and it gives a false positive warning about possible uninitialized data
> > usage.
> > While data flow analysis is not perfect, it is weird that this used to
> > happen on 32 bit but not on 64 bit.
> > Meanwhile, after updating some other packages (not sure which), but
> > still the same gcc version, the report on the test case also happens on
> > 64 bit, while the original, unstripped file, as part of mintty, still
> > works without error on 64 bit, which is even weirder.
> > I have not yet had the opportunity to test this on Linux, sorry, so I'm
> > reporting it here.
> > Thomas
>
> If you mean this warning:
>
> m0.c: In function 'do_bidi':
> m0.c:256:12: error: '*types[0]' may be used uninitialized [-Werror=maybe-uninitialized]
>
> This warning is correct, because as far as gcc is concerned, count could
> be 0, and in this case types[0] will be uninitialized (and doesn't even
> exist, since it's declared as 'uchar types[count];').

I'm not familiar with cygwin repositories, where can I find the source for this?

I'm looking at the warnings and wondering if it's from a "flexible
array" declaration in a typedef.

-- 
Joel Rees

http://reiisi.blogspot.jp/p/novels-i-am-writing.html

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