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From: Jiri Slaby <jslaby@suse.cz>
To: Peter Zijlstra <peterz@infradead.org>,
	Vegard Nossum <vegard.nossum@oracle.com>
Cc: linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"Luis R . Rodriguez" <mcgrof@kernel.org>,
	stable@vger.kernel.org, Ming Lei <ming.lei@canonical.com>,
	Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 01/12] extarray: define helpers for arrays defined in linker scripts
Date: Mon, 17 Oct 2016 11:01:13 +0200	[thread overview]
Message-ID: <186f8242-3f8d-31cd-a8e8-9743bbc1c1fd@suse.cz> (raw)
In-Reply-To: <20161017083315.GA29322@worktop.vlan200.pylonone.local>

On 10/17/2016, 10:33 AM, Peter Zijlstra wrote:
> On Sun, Oct 16, 2016 at 05:16:05PM +0200, Vegard Nossum wrote:
>> The test in this loop:
>>
>> 	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
>>
>> was getting completely compiled out by my gcc, 7.0.0 20160520. The result
>> was that the loop was going beyond the end of the builtin_fw array and
>> giving me a page fault when trying to dereference b_fw->name.
>>
>> This is because __start_builtin_fw and __end_builtin_fw are both declared
>> as (separate) arrays, and so gcc conludes that b_fw can never point to
>> __end_builtin_fw.
>>
> 
> Urgh, isn't that the kind of 'optimizations' we should shoot in the head
> for the kernel? Just like the -fno-strict-aliassing crap?

Unfortunately, there is no such switch for this optimization.

On the top of that, it's incorrect C according to the standard. So it is
as correct as expecting 0 printed here: 'int zero; printf("%d\n",
zero);'. It never worked, not even with gcc 4 and maybe older. We were
just lucky.

thanks,
-- 
js
suse labs

  reply	other threads:[~2016-10-17  9:01 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-16 15:16 [PATCH 00/12] external array access helpers Vegard Nossum
2016-10-16 15:16 ` [PATCH 01/12] extarray: define helpers for arrays defined in linker scripts Vegard Nossum
2016-10-17  7:04   ` Greg Kroah-Hartman
2016-10-17  8:33   ` Peter Zijlstra
2016-10-17  9:01     ` Jiri Slaby [this message]
2016-10-17  9:09       ` Peter Zijlstra
2016-10-17 11:27         ` Vegard Nossum
2016-10-17 11:45           ` Peter Zijlstra
2016-10-18  8:08             ` Vegard Nossum
2016-10-18 21:18               ` Luis R. Rodriguez
2016-10-19  8:18                 ` Richard Biener
2016-10-19  9:13                   ` Peter Zijlstra
2016-10-19  9:33                     ` Richard Biener
2016-10-19 10:25                       ` Peter Zijlstra
2016-10-19 11:11                         ` Richard Biener
2016-10-19 11:31                           ` Peter Zijlstra
2016-11-02 12:11                         ` Markus Trippelsdorf
2016-11-02 12:14                           ` Richard Biener
2016-11-02 15:02                             ` Linus Torvalds
2016-10-19  7:16             ` Jiri Slaby
2016-10-16 15:16 ` [PATCH 02/12] firmware: declare {__start,__end}_builtin_fw as external array Vegard Nossum
2016-10-16 15:16 ` [PATCH 03/12] ftrace: declare __{start,stop}_mcount_loc " Vegard Nossum
2016-10-16 15:16 ` [PATCH 04/12] tracing: declare __{start,stop}_{annotated_,}branch_profile " Vegard Nossum
2016-10-16 15:16 ` [PATCH 05/12] kprobes: declare __{start,stop}_kprobe_blacklist " Vegard Nossum
2016-10-17  5:53   ` Masami Hiramatsu
2016-10-16 15:16 ` [PATCH 06/12] tracing: declare __{start,stop}_ftrace_events " Vegard Nossum
2016-10-16 15:16 ` [PATCH 07/12] tracing: declare __{start,stop}_ftrace_enum_maps " Vegard Nossum
2016-10-16 15:16 ` [PATCH 08/12] tracing: declare __trace_bprintk_fmt/__tracepoint_str as external arrays Vegard Nossum
2016-10-16 15:16 ` [PATCH 09/12] tracing: declare __{start,stop}_syscalls_metadata as external array Vegard Nossum
2016-10-16 15:16 ` [PATCH 10/12] serial_core: declare __earlycon_table{,_end} " Vegard Nossum
2016-10-16 15:16 ` [PATCH 11/12] jump_label: declare jump table " Vegard Nossum
2016-10-16 16:25   ` Peter Zijlstra
2016-10-16 16:50     ` Vegard Nossum
2016-10-16 17:44       ` Peter Zijlstra
2016-10-17 21:33       ` Steven Rostedt
2016-10-16 15:16 ` [PATCH 12/12] dynamic debug: declare " Vegard Nossum
2016-10-16 16:14 ` [PATCH 00/12] external array access helpers Greg Kroah-Hartman
2016-10-16 17:05   ` Vegard Nossum
2016-10-17  7:02     ` Greg Kroah-Hartman
2016-10-17  6:26   ` Jiri Slaby

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