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Re: -fsanitize=undefined detects undefined behaviour in signed shift ove
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From: |
Thomas Dickey |
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Subject: |
Re: -fsanitize=undefined detects undefined behaviour in signed shift overflow |
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Date: |
Sat, 8 May 2021 16:31:46 -0400 |
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User-agent: |
Mutt/1.10.1 (2018-07-13) |
On Sat, May 08, 2021 at 08:55:48PM +0100, Sergei Trofimovich wrote:
> Hello ncurses maintainers!
>
> In search for an unrelated bug I built a few local tools with
> `-fsanitize=undefined` gcc option to catch an suspected undefined
> behaviour.
>
> Among other things ncurses was flagged in ncurses-based applications as:
> ncurses/tinfo/read_entry.c:111:19:
> runtime error: left shift of 255 by 24 places cannot be represented in
> type 'int'
>
> which looks like a real (perhaps minor) problem:
I'm aware of the warning, but don't see a way to detect the overflow
and not elicit a warning about undefined behavior.
A patch would help discussion.
(earlier this week I noticed a change by someone to eliminate undefined
behavior which doesn't produce a compiler warning with/without the change,
_and_ the change causes incorrect behavior -- something to keep in mind)
--
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net
ftp://ftp.invisible-island.net
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