From: Oleg Nesterov <oleg@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-kernel@vger.kernel.org,
Nick Desaulniers <ndesaulniers@google.com>,
"Eric W . Biederman" <ebiederm@xmission.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-arch@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
Paul Burton <paul.burton@mips.com>,
James Hogan <jhogan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Deepa Dinamani <deepa.kernel@gmail.com>,
Christian Brauner <christian@brauner.io>,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
linux-mips@vger.kernel.org
Subject: Re: [PATCH] signal: fix building with clang
Date: Thu, 7 Mar 2019 16:28:05 +0100 [thread overview]
Message-ID: <20190307152805.GA25101@redhat.com> (raw)
In-Reply-To: <20190307091218.2343836-1-arnd@arndb.de>
On 03/07, Arnd Bergmann wrote:
>
> clang warns about the sigset_t manipulating functions (sigaddset, sigdelset,
> sigisemptyset, ...) because it performs semantic analysis before discarding
> dead code, unlike gcc that does this in the reverse order.
>
> The result is a long list of warnings like:
>
> In file included from arch/arm64/include/asm/ftrace.h:21:
> include/linux/compat.h:489:10: error: array index 3 is past the end of the array (which contains 2 elements) [-Werror,-Warray-bounds]
> case 2: v.sig[3] = (set->sig[1] >> 32); v.sig[2] = set->sig[1];
stupid question... I have no idea if this can work or not, but may be we can just do
--- x/Makefile
+++ x/Makefile
@@ -701,6 +701,7 @@ KBUILD_CPPFLAGS += $(call cc-option,-Qun
KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
+KBUILD_CFLAGS += $(call cc-disable-warning, array-bounds)
# Quiet clang warning: comparison of unsigned expression < 0 is always false
KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
# CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
?
> As a (rather ugly) workaround,
Yes :/
But I am not going to argue, just a couple of questions.
> I turn the nice switch()/case statements
> into preprocessor conditionals, and where that is not possible, use the
> '%' operator
I can't say what looks worse... to me it would be either use ifdef's or %'s
everywhere in signal.h, with this patch the code doesn't look consistent.
But I won't insist.
> static inline int sigisemptyset(sigset_t *set)
> {
> - switch (_NSIG_WORDS) {
> - case 4:
> - return (set->sig[3] | set->sig[2] |
> - set->sig[1] | set->sig[0]) == 0;
> - case 2:
> - return (set->sig[1] | set->sig[0]) == 0;
> - case 1:
> - return set->sig[0] == 0;
> - default:
> - BUILD_BUG();
> - return 0;
> - }
> +#if _NSIG_WORDS == 4
> + return (set->sig[3] | set->sig[2] |
> + set->sig[1] | set->sig[0]) == 0;
> +#elif _NSIG_WORDS == 2
> + return (set->sig[1] | set->sig[0]) == 0;
> +#elif _NSIG_WORDS == 1
> + return set->sig[0] == 0;
> +#else
> + BUILD_BUG();
> +#endif
> }
Or perhaps we can simply rewrite this and other helpers?
I don't think that, say,
static inline int sigisemptyset(sigset_t *set)
{
for (i = 0; i < ARRAY_SIZE(set->sig); ++i)
set->sig[i] = 0;
}
will make asm worse...
Oleg.
next prev parent reply other threads:[~2019-03-07 15:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-07 9:11 [PATCH] signal: fix building with clang Arnd Bergmann
2019-03-07 10:03 ` Christian Brauner
2019-03-07 15:28 ` Oleg Nesterov [this message]
2019-03-07 15:37 ` Arnd Bergmann
2019-03-07 16:46 ` Oleg Nesterov
2019-03-07 18:41 ` Nick Desaulniers
2019-03-07 21:45 ` Arnd Bergmann
2019-03-08 0:22 ` Nick Desaulniers
2019-03-08 0:27 ` Joe Perches
2019-03-08 21:09 ` Nick Desaulniers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190307152805.GA25101@redhat.com \
--to=oleg@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=christian@brauner.io \
--cc=deepa.kernel@gmail.com \
--cc=ebiederm@xmission.com \
--cc=gustavo@embeddedor.com \
--cc=jhogan@kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=ndesaulniers@google.com \
--cc=paul.burton@mips.com \
--cc=ralf@linux-mips.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).