Am 27.10.2021 um 12:55 schrieb Hannes Domani:
Am Mittwoch, 27. Oktober 2021, 11:19:19 MESZ hat Thomas Wolff <t...@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];').
Thanks for the hint. I acknowledge that the analyser cannot know that
count > 0 here. But if types[0] exists, it cannot be unitialized so the
wording of the warning is not correct in this case. Anyway, this leads
to a less obtrusive workaround than the current one.
Thomas
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