From: "Hunt, David" <david.hunt@intel.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: Nikhil Rao <nikhil.rao@intel.com>,
bruce.richardson@intel.com,
Konstantin Ananyev <konstantin.ananyev@intel.com>,
dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] eal: fix bug in x86 cmpset
Date: Fri, 10 Feb 2017 11:56:27 +0000 [thread overview]
Message-ID: <e50b9a09-f2d8-1477-1760-d65fcef53c16@intel.com> (raw)
In-Reply-To: <2295899.BebvH11edl@xps13>
On 10/2/2017 10:53 AM, Thomas Monjalon wrote:
> 2017-02-10 10:39, Hunt, David:
>> On 9/2/2017 4:53 PM, Thomas Monjalon wrote:
>>> 2016-11-06 22:09, Thomas Monjalon:
>>>> 2016-09-29 18:34, Thomas Monjalon:
>>>>> 2016-09-30 02:54, Nikhil Rao:
>>>>>> The original code used movl instead of xchgl, this caused
>>>>>> rte_atomic64_cmpset to use ebx as the lower dword of the source
>>>>>> to cmpxchg8b instead of the lower dword of function argument "src".
>>>>> Could you please start the explanation with a statement of
>>>>> what is wrong from an user point of view?
>>>>> It could help to understand how severe it is.
>>>> Please, we need a clear explanation of the bug, and an acknowledgement.
>>> Should we close this bug?
>> I took a few minutes to look at this, and the issue can easily be
>> reproduced with a small snippet of code.
>> With the 'mov', the lower dword of the result is incorrect. This is
>> resolved by using 'xchgl'.
>>
>> void main()
>> {
>> uint64_t a = 0xff000000ff;
>>
>> rte_atomic64_cmpset( &a, 0xff000000ff, 0xfa000000fa);
>> printf("0x%lx\n", a);
>> }
>>
>> When using 'mov', the result is 0xfa00000000
>> When using 'xchgl', the result is 0xfa000000fa, as expected.
> This operation is used a lot in drivers for link status.
>
> I think we need to clearly explain what was the consequence of this bug.
Agreed. It's probably also worth noting that its only on the __PIC__ enabled
codepath so would have more of an affect on the distros.
next prev parent reply other threads:[~2017-02-10 11:56 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-29 21:24 Nikhil Rao
2016-09-29 13:05 ` Christian Ehrhardt
2016-09-29 13:16 ` Rao, Nikhil
2016-09-29 14:21 ` Thomas Monjalon
2016-09-29 16:34 ` Thomas Monjalon
2016-11-06 21:09 ` Thomas Monjalon
2017-02-09 16:53 ` Thomas Monjalon
2017-02-10 10:39 ` Hunt, David
2017-02-10 10:53 ` Thomas Monjalon
2017-02-10 11:56 ` Hunt, David [this message]
2017-02-10 16:46 ` Stephen Hemminger
2017-03-09 15:39 ` Thomas Monjalon
2017-09-04 13:02 ` Bruce Richardson
2017-09-04 13:06 ` Bruce Richardson
2017-10-26 22:03 ` Thomas Monjalon
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