linux-kernel - Re: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test

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Date:	Mon, 16 May 2016 11:25:12 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Dmitry Safonov <0x7f454c46@...il.com>,
	Shuah Khan <shuahkh@....samsung.com>,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test

On Mon, May 16, 2016 at 9:24 AM, Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
> On 05/16/2016 04:54 PM, Ingo Molnar wrote:
>>
>>
>> * Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
>>
>>> Should print on success:
>>> [root@...alhost ~]# ./test_mremap_vdso_32
>>>         AT_SYSINFO_EHDR is 0xf773f000
>>> [NOTE]  Moving vDSO: [f773f000, f7740000] -> [a000000, a001000]
>>> [OK]
>>> Or segfault if landing was bad (before patches):
>>> [root@...alhost ~]# ./test_mremap_vdso_32
>>>         AT_SYSINFO_EHDR is 0xf774f000
>>> [NOTE]  Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
>>> Segmentation fault (core dumped)
>>
>>
>> Can the segfault be caught and recovered from, to print a proper failure
>> message?
>
>
> Will add segfault handler, thanks.
>

It may be more complicated that that.  Glibc is likely to explode if
this happens, and the headers are sufficiently screwed up that it's
awkward to bypass glibc and call rt_sigaction directly.  I have a test
that does the latter, though, so it's at least possible, but I'm
unconvinced it's worth it just for an error message.

-- 
Andy Lutomirski
AMA Capital Management, LLC