linux-kernel - RE: next build: 235 warnings 3 failures (next/next-20151117)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 18 Nov 2015 10:22:04 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Arnd Bergmann' <arnd@...db.de>, Will Deacon <will.deacon@....com>
CC:	Catalin Marinas <catalin.marinas@....com>,
	"kernel-build-reports@...ts.linaro.org" 
	<kernel-build-reports@...ts.linaro.org>,
	"olof@...om.net" <olof@...om.net>,
	David Miller <davem@...emloft.net>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: next build: 235 warnings 3 failures (next/next-20151117)

From: Arnd Bergmann
> Sent: 17 November 2015 19:17
> On Tuesday 17 November 2015 17:12:37 Will Deacon wrote:
> > On Tue, Nov 17, 2015 at 06:03:40PM +0100, Arnd Bergmann wrote:
> > > On Tuesday 17 November 2015 16:44:53 Will Deacon wrote:
> > > > > 8<----
> > > > > Subject: ARM64: make smp_load_acquire() work with const arguments
> > > > >
> > > > > smp_load_acquire() uses typeof() to declare a local variable for temporarily
> > > > > storing the output of the memory access. This fails when the argument is
> > > > > constant, because the assembler complains about using a constant register
> > > > > as output:
> > > > >
> > > > >  arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1'
> > > > >  used as 'asm' output
> > > >
> > > > Do you know the usage in the kernel causing this warning?
> > >
> > > A newly introduced function in include/net/sock.h:
> > >
> > > static inline int sk_state_load(const struct sock *sk)
> > > {
> > >         return smp_load_acquire(&sk->sk_state);
> > > }
> >
> > Hmm, maybe we could play a similar trick to READ_ONCE by declaring an
> > anonymous union and writing through the non-const member?
> 
> Yes, I think that would work, if you think we need to care about the
> case where we read into a structure.

How are you going to find the right type/size for the non-const member of the union?
If the type/size is fixed then why use typeof()?

If the variable being read (sk->sk_state above) might only be 8 or 16 bits then
you might be able to use sizeof() to select between code paths.

	David

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/