From: Jan Beulich <jbeulich@suse.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org, Wei Liu <wl@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH 1/3] x86/mm: do not attempt to convert _PAGE_GNTTAB to a boolean
Date: Tue, 5 May 2020 15:47:43 +0200 [thread overview]
Message-ID: <20332b18-960c-a180-8150-55fae60bdc6e@suse.com> (raw)
In-Reply-To: <20200505092454.9161-2-roger.pau@citrix.com>
On 05.05.2020 11:24, Roger Pau Monne wrote:
> Clang 10 complains with:
>
> mm.c:1239:10: error: converting the result of '<<' to a boolean always evaluates to true
> [-Werror,-Wtautological-constant-compare]
> if ( _PAGE_GNTTAB && (l1e_get_flags(l1e) & _PAGE_GNTTAB) &&
> ^
> xen/include/asm/x86_64/page.h:161:25: note: expanded from macro '_PAGE_GNTTAB'
> #define _PAGE_GNTTAB (1U<<22)
> ^
This is a rather odd warning. Do they also warn for "if ( 0 )"
or "do { } while ( 0 )", as we use in various places? There's
no difference to me between a plain number and a constant
composed via an expression.
> Remove the conversion of _PAGE_GNTTAB to a boolean, since the and
> operation performed afterwards will already return false if the value
> of the macro is 0.
I'm sorry, but no. The expression was put there on purpose by
0932210ac095 ("x86: Address "Bitwise-and with zero
CONSTANT_EXPRESSION_RESULT" Coverity issues"), and the
description there is clearly telling us that this wants to stay
unless Coverity changed in the meantime. Otherwise I'm afraid
a more elaborate solution will be needed to please both. Or a
more simplistic one, like using "#if _PAGE_GNTTAB" around the
construct.
Jan
next prev parent reply other threads:[~2020-05-05 13:48 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 9:24 [PATCH 0/3] build: fixes for clang 10 Roger Pau Monne
2020-05-05 9:24 ` [PATCH 1/3] x86/mm: do not attempt to convert _PAGE_GNTTAB to a boolean Roger Pau Monne
2020-05-05 13:47 ` Jan Beulich [this message]
2020-05-05 14:11 ` Roger Pau Monné
2020-05-05 14:59 ` Jan Beulich
2020-05-05 9:24 ` [PATCH 2/3] configure: also add EXTRA_PREFIX to {CPP/LD}FLAGS Roger Pau Monne
2020-05-06 13:07 ` Wei Liu
2020-05-22 8:41 ` Bertrand Marquis
2020-05-22 9:05 ` Wei Liu
2020-05-22 9:37 ` Bertrand Marquis
2020-05-22 9:59 ` Wei Liu
2020-05-22 11:19 ` Roger Pau Monné
2020-05-22 11:40 ` Bertrand Marquis
2020-05-22 11:41 ` Wei Liu
2020-05-05 9:24 ` [PATCH 3/3] tools/libxl: disable clang indentation check for the disk parser Roger Pau Monne
2020-05-06 13:07 ` Wei Liu
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