From: Arnd Bergmann <arnd@arndb.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andi Kleen <andi@firstfloor.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andi Kleen <ak@linux.intel.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>
Subject: Re: [PATCH 01/17] kbuild: Disable -Waddress-of-packed-member for gcc 9
Date: Fri, 22 Mar 2019 17:57:09 +0100 [thread overview]
Message-ID: <CAK8P3a3Zpkz+TNYE_PtY0dS=jxi1G1VtXWAmiABAS7nRMUkGgA@mail.gmail.com> (raw)
In-Reply-To: <20190322163954.GG7905@worktop.programming.kicks-ass.net>
On Fri, Mar 22, 2019 at 5:40 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Mar 22, 2019 at 02:58:51PM +0100, Arnd Bergmann wrote:
> > On Thu, Mar 21, 2019 at 11:00 PM Andi Kleen <andi@firstfloor.org> wrote:
> > >
> > > From: Andi Kleen <ak@linux.intel.com>
> > >
> > > This warning is very noisy in a default build with gcc 9.
> > > Move it into W=2 only.
> > >
> > > Cc: arnd@arndb.de
> > > Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> > > Signed-off-by: Andi Kleen <ak@linux.intel.com>
> >
> > I think W=2 is too aggressive. On many architectures, this finds
> > real bugs and the false positives tend to be trivial to fix
> > (by removing the bogus __packed annotation), which improves
> > the generated code in the process.
> >
> > Moving it to W=1 for the moment is probably fine, but ideally
> > I think we should fix the kernel to behave according to the
> > C standard.
>
> Lol... we're actively moving away from the C standard on many places.
>
> Why does the silly compiler think it is a problem to take the address of
> a member of a packed structure? That sounds like something that's
> perfectly fine and useful.
The problem is casting a pointer of an unaligned variable to one
of higher alignment and passing that to a function that does not
expect unaligned data.
On CPUs that don't have unaligned load/store instructions, this
causes an alignment fault, which will have to be fixed up in
software by doing a bytewise access or crash the system.
Arnd
next prev parent reply other threads:[~2019-03-22 16:57 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-21 21:59 Fixes and cleanup from LTO tree Andi Kleen
2019-03-21 21:59 ` [PATCH 01/17] kbuild: Disable -Waddress-of-packed-member for gcc 9 Andi Kleen
2019-03-22 13:58 ` Arnd Bergmann
2019-03-22 16:31 ` Andi Kleen
2019-03-22 16:39 ` Peter Zijlstra
2019-03-22 16:57 ` Arnd Bergmann [this message]
2019-03-22 16:58 ` Andi Kleen
2019-03-25 16:27 ` David Laight
2019-04-01 1:04 ` Masahiro Yamada
2019-03-21 21:59 ` [PATCH 02/17] x86, lto: Mark all top level asm statements as .text Andi Kleen
2019-03-26 17:03 ` Thomas Gleixner
2019-03-26 21:38 ` Andi Kleen
2019-03-26 22:25 ` Thomas Gleixner
2019-03-27 0:55 ` Andi Kleen
2019-03-27 1:08 ` Andi Kleen
2019-03-27 14:20 ` Thomas Gleixner
2019-03-27 14:39 ` Ingo Molnar
2019-03-27 14:59 ` Andi Kleen
2019-03-27 15:08 ` Thomas Gleixner
2019-03-27 15:45 ` Andi Kleen
2019-03-27 19:08 ` Thomas Gleixner
2019-03-27 20:40 ` Andi Kleen
2019-03-27 21:55 ` Thomas Gleixner
2019-03-27 22:29 ` Andi Kleen
2019-03-27 22:50 ` Thomas Gleixner
2019-04-02 8:54 ` Thomas Gleixner
2019-03-21 21:59 ` [PATCH 03/17] x86: Don't inline __const_udelay Andi Kleen
2019-03-21 21:59 ` [PATCH 04/17] init: Add __noreorder and mark initcalls __noreorder Andi Kleen
2019-03-21 21:59 ` [PATCH 05/17] Use C version for SYSCALL_ALIAS Andi Kleen
2019-03-21 21:59 ` [PATCH 06/17] locking/core: Mark spinlocks noinline when inline spinlocks are disabled Andi Kleen
2019-03-21 21:59 ` [PATCH 07/17] amdkfd: Fix extern declaration Andi Kleen
2019-03-21 22:00 ` [PATCH 08/17] x86/speculation: Fix __initconst in bugs.c Andi Kleen
2019-03-26 17:24 ` Thomas Gleixner
2019-03-21 22:00 ` [PATCH 09/17] x86/kvm: Make steal_time visible Andi Kleen
2019-03-21 22:00 ` [PATCH 10/17] delta: Fix buffer overrun in delta_ipc_open Andi Kleen
2019-04-01 13:37 ` Hugues FRUCHET
2019-04-01 16:54 ` Andi Kleen
2019-04-02 9:56 ` Hugues FRUCHET
2019-03-21 22:00 ` [PATCH 11/17] x86/kprobes: Make trampoline_handler global and visible Andi Kleen
2019-03-23 9:45 ` Masami Hiramatsu
2019-03-23 14:35 ` Andi Kleen
2019-03-25 1:53 ` Masami Hiramatsu
2019-03-21 22:00 ` [PATCH 12/17] afs: Avoid section confusion in CM_NAME Andi Kleen
2019-03-21 22:00 ` [PATCH 13/17] ASoC: AMD: Fix incorrect extern Andi Kleen
2019-03-21 22:00 ` [PATCH 14/17] crypto: Don't mark AES tables const and cacheline_aligned Andi Kleen
2019-03-26 8:42 ` Rasmus Villemoes
2019-03-26 18:30 ` Andi Kleen
2019-03-21 22:00 ` [PATCH 15/17] x86/hyperv: Make hv_vcpu_is_preempted visible Andi Kleen
2019-03-26 8:15 ` Yi Sun
2019-03-21 22:00 ` [PATCH 16/17] x86/xen: Mark xen_vcpu_stolen as __visible Andi Kleen
2019-03-21 22:00 ` [PATCH 17/17] dm: Fix const confusion in dm Andi Kleen
2019-03-22 8:34 ` [PATCH 12/17] afs: Avoid section confusion in CM_NAME David Howells
2019-03-26 17:00 ` Fixes and cleanup from LTO tree Thomas Gleixner
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