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From: Ferruh Yigit <ferruh.yigit@intel.com>
To: Thomas Monjalon <thomas@monjalon.net>,
	"Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	Akhil Goyal <akhil.goyal@nxp.com>,
	"Trahe, Fiona" <fiona.trahe@intel.com>
Cc: David Marchand <david.marchand@redhat.com>,
	Anoob Joseph <anoobj@marvell.com>,
	"Kusztal, ArkadiuszX" <arkadiuszx.kusztal@intel.com>,
	dev@dpdk.org, "Richardson, Bruce" <bruce.richardson@intel.com>,
	nhorman@tuxdriver.com, "Mcnamara, John" <john.mcnamara@intel.com>,
	dodji@seketeli.net, Andrew Rybchenko <arybchenko@solarflare.com>,
	aconole@redhat.com, bluca@debian.org, ktraynor@redhat.com
Subject: Re: [dpdk-dev] [PATCH v2 4/4] add ABI checks
Date: Mon, 3 Feb 2020 17:40:20 +0000	[thread overview]
Message-ID: <78e8ecf2-2239-897e-e34c-aee7227f3d42@intel.com> (raw)
In-Reply-To: <7566080.EvYhyI6sBW@xps>

On 2/3/2020 5:09 PM, Thomas Monjalon wrote:
> 03/02/2020 10:30, Ferruh Yigit:
>> On 2/2/2020 2:41 PM, Ananyev, Konstantin wrote:
>>> 02/02/2020 14:05, Thomas Monjalon:
>>>> 31/01/2020 15:16, Trahe, Fiona:
>>>>> On 1/30/2020 8:18 PM, Thomas Monjalon wrote:
>>>>>> 30/01/2020 17:09, Ferruh Yigit:
>>>>>>> On 1/29/2020 8:13 PM, Akhil Goyal wrote:
>>>>>>>>
>>>>>>>> I believe these enums will be used only in case of ASYM case which is experimental.
>>>>>>>
>>>>>>> Independent from being experiment and not, this shouldn't be a problem, I think
>>>>>>> this is a false positive.
>>>>>>>
>>>>>>> The ABI break can happen when a struct has been shared between the application
>>>>>>> and the library (DPDK) and the layout of that memory know differently by
>>>>>>> application and the library.
>>>>>>>
>>>>>>> Here in all cases, there is no layout/size change.
>>>>>>>
>>>>>>> As to the value changes of the enums, since application compiled with old DPDK,
>>>>>>> it will know only up to '6', 7 and more means invalid to the application. So it
>>>>>>> won't send these values also it should ignore these values from library. Only
>>>>>>> consequence is old application won't able to use new features those new enums
>>>>>>> provide but that is expected/normal.
>>>>>>
>>>>>> If library give higher value than expected by the application,
>>>>>> if the application uses this value as array index,
>>>>>> there can be an access out of bounds.
>>>>>
>>>>> [Fiona] All asymmetric APIs are experimental so above shouldn't be a problem.
>>>>> But for the same issue with sym crypto below, I believe Ferruh's explanation makes
>>>>> sense and I don't see how there can be an API breakage.
>>>>> So if an application hasn't compiled against the new lib it will be still using the old value
>>>>> which will be within bounds. If it's picking up the higher new value from the lib it must
>>>>> have been compiled against the lib so shouldn't have problems.
>>>>
>>>> You say there is no ABI issue because the application will be re-compiled
>>>> for the updated library. Indeed, compilation fixes compatibility issues.
>>>> But this is not relevant for ABI compatibility.
>>>> ABI compatibility means we can upgrade the library without recompiling
>>>> the application and it must work.
>>>> You think it is a false positive because you assume the application
>>>> "picks" the new value. I think you miss the case where the new value
>>>> is returned by a function in the upgraded library.
>>>>
>>>>> There are also no structs on the API which contain arrays using this
>>>>> for sizing, so I don't see an opportunity for an appl to have a
>>>>> mismatch in memory addresses.
>>>>
>>>> Let me demonstrate where the API may "use" the new value
>>>> RTE_CRYPTO_AEAD_CHACHA20_POLY1305 and how it impacts the application.
>>>>
>>>> Once upon a time a DPDK application counting the number of devices
>>>> supporting each AEAD algo (in order to find the best supported algo).
>>>> It is done in an array indexed by algo id:
>>>> int aead_dev_count[RTE_CRYPTO_AEAD_LIST_END];
>>>> The application is compiled with DPDK 19.11,
>>>> where RTE_CRYPTO_AEAD_LIST_END = 3.
>>>> So the size of the application array aead_dev_count is 3.
>>>> This binary is run with DPDK 20.02,
>>>> where RTE_CRYPTO_AEAD_CHACHA20_POLY1305 = 3.
>>>> When calling rte_cryptodev_info_get() on a device QAT_GEN3,
>>>> rte_cryptodev_info.capabilities.sym.aead.algo is set to
>>>> RTE_CRYPTO_AEAD_CHACHA20_POLY1305 (= 3).
>>>> The application uses this value:
>>>> ++ aead_dev_count[info.capabilities.sym.aead.algo];
>>>> The application is crashing because of out of bound access.
>>>
>>> I'd say this is an example of bad written app.
>>> It probably should check that returned by library value doesn't
>>> exceed its internal array size.
>>
>> +1
>>
>> Application should ignore values >= MAX.
> 
> Of course, blaming the API user is a lot easier than looking at the API.
> Here the API has RTE_CRYPTO_AEAD_LIST_END which can be understood
> as the max value for the application.
> Value ranges are part of the ABI compatibility contract.
> It seems you expect the application developer to be aware that
> DPDK could return a higher value, so the application should
> check every enum values after calling an API. CRAZY.
> 
> When we decide to announce an ABI compatibility and do some marketing,
> everyone is OK. But when we need to really make our ABI compatible,
> I see little or no effort. DISAPPOINTING.

This is not to blame the user or to do less work, this is more sane approach
that library provides the _END/_MAX value and application uses it as valid range
check.

> 
>> Do you suggest we don't extend any enum or define between ABI breakage releases
>> to be sure bad written applications not affected?
> 
> I suggest we must consider not breaking any assumption made on the API.
> Here we are breaking the enum range because nothing mentions _LIST_END
> is not really the absolute end of the enum.
> The solution is to make the change below in 20.02 + backport in 19.11.1:
> 
> - _LIST_END
> + _LIST_END, /* an ABI-compatible version may increase this value */
> + _LIST_MAX = _LIST_END + 42 /* room for ABI-compatible additions */
> };
> 

What is the point of "_LIST_MAX" here?

Application should know the "_LIST_END" of when it has been compiled for the
valid range check. Next time it is compiled "_LIST_END" may be different value
but same logic applies.

When "_LIST_END" is missing, application can't protect itself, in that case
library should send only the values application knows when it is compiled, this
means either we can't extend our enum/defines until next ABI breakage, or we
need to do ABI versioning to the functions that returns an enum each time enum
value extended.

I believe it is saner to provide _END/_MAX values to the application to use. And
if required comment them to clarify the expected usage.

But in above suggestion application can't use or rely on "_LIST_MAX", it doesn't
mean anything to application.

> Then *_LIST_END values could be ignored by libabigail with such a change.
> 
> If such a patch is not done by tomorrow, I will have to revert
> Chacha-Poly commits before 20.02-rc2, because
> 
> 1/ LIST_END, without any comment, means "size of range"
> 2/ we do not blame users for undocumented ABI changes
> 3/ we respect the ABI compatibility contract
> 
> 


  parent reply	other threads:[~2020-02-03 17:40 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-20 15:20 [dpdk-dev] [PATCH] " David Marchand
2019-12-20 15:32 ` Richardson, Bruce
2019-12-20 16:20   ` Kinsella, Ray
2019-12-20 21:00     ` Thomas Monjalon
2020-01-06 13:17       ` Aaron Conole
2020-01-15 13:07         ` Burakov, Anatoly
2020-01-14 23:19     ` Thomas Monjalon
2020-01-15 11:33       ` Neil Horman
2020-01-15 12:38         ` Thomas Monjalon
2020-01-16 11:52           ` Neil Horman
2020-01-16 14:20             ` Thomas Monjalon
2020-01-16 18:49               ` Neil Horman
2020-01-16 20:01                 ` Thomas Monjalon
2020-01-17 19:01                   ` Neil Horman
2020-01-17 21:26                     ` David Marchand
2019-12-20 20:25 ` Neil Horman
2020-01-29 17:26 ` [dpdk-dev] [PATCH v2 0/4] " David Marchand
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 1/4] hash: fix meson headers packaging David Marchand
2020-01-30 10:12     ` Luca Boccassi
2020-01-30 10:54       ` David Marchand
2020-01-30 10:56         ` Luca Boccassi
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 2/4] build: split build helper David Marchand
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 3/4] build: test meson installation David Marchand
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 4/4] add ABI checks David Marchand
2020-01-29 17:42     ` Thomas Monjalon
2020-01-29 18:10       ` Anoob Joseph
2020-01-29 20:03         ` David Marchand
2020-01-29 20:13           ` Akhil Goyal
2020-01-30 16:09             ` Ferruh Yigit
2020-01-30 20:18               ` Thomas Monjalon
2020-01-31  9:03                 ` Ferruh Yigit
2020-01-31 10:26                   ` Ananyev, Konstantin
2020-01-31 14:16                 ` Trahe, Fiona
2020-02-02 13:05                   ` Thomas Monjalon
2020-02-02 14:41                     ` Ananyev, Konstantin
2020-02-03  9:30                       ` Ferruh Yigit
2020-02-03 11:50                         ` Neil Horman
2020-02-03 13:09                           ` Ferruh Yigit
2020-02-03 14:00                             ` Dodji Seketeli
2020-02-03 14:46                               ` Ferruh Yigit
2020-02-03 15:08                             ` Trahe, Fiona
2020-02-03 17:09                         ` Thomas Monjalon
2020-02-03 17:34                           ` Thomas Monjalon
2020-02-03 18:55                             ` Ray Kinsella
2020-02-03 21:07                               ` Thomas Monjalon
2020-02-04  9:46                                 ` Ferruh Yigit
2020-02-04 10:24                                 ` Thomas Monjalon
2020-02-04 12:44                                   ` Trahe, Fiona
2020-02-04 15:52                                     ` Trahe, Fiona
2020-02-04 15:59                                       ` Thomas Monjalon
2020-02-04 17:46                                         ` Trahe, Fiona
2020-02-13 14:51                                           ` Kusztal, ArkadiuszX
2020-03-16 12:57                                             ` Trahe, Fiona
2020-03-16 13:09                                               ` Thomas Monjalon
2020-03-17 13:27                                                 ` Kusztal, ArkadiuszX
2020-03-17 15:10                                                   ` Thomas Monjalon
2020-03-17 19:10                                                     ` Kusztal, ArkadiuszX
2020-02-04 12:57                                   ` Kevin Traynor
2020-02-04 14:44                                   ` Aaron Conole
2020-02-04 19:49                                     ` Neil Horman
2020-02-04  9:51                               ` David Marchand
2020-02-04 10:10                                 ` Trahe, Fiona
2020-02-04 10:38                                   ` Thomas Monjalon
2020-02-05 11:10                                 ` Ray Kinsella
2020-02-03 17:40                           ` Ferruh Yigit [this message]
2020-02-03 18:40                             ` Thomas Monjalon
2020-02-04  9:19                               ` Ferruh Yigit
2020-02-04  9:45                                 ` Thomas Monjalon
2020-02-04  9:56                                   ` Ferruh Yigit
2020-02-04 10:08                                     ` Bruce Richardson
2020-02-04 10:17                                     ` Kevin Traynor
2020-02-04 10:16                             ` Akhil Goyal
2020-02-04 10:28                               ` Thomas Monjalon
2020-02-04 10:32                                 ` Akhil Goyal
2020-02-04 11:35                                   ` Bruce Richardson
2020-02-04 22:10                                   ` Neil Horman
2020-02-05  6:16                                     ` [dpdk-dev] [EXT] " Anoob Joseph
2020-02-05 14:33                                       ` Trahe, Fiona
2020-02-04 21:59                               ` [dpdk-dev] " Neil Horman
2020-01-30 13:06         ` Trahe, Fiona
2020-01-30 15:59           ` Thomas Monjalon
2020-01-30 16:42             ` Ferruh Yigit
2020-01-30 23:49             ` Ananyev, Konstantin
2020-01-31  9:07               ` Ferruh Yigit
2020-01-31  9:37                 ` Ananyev, Konstantin
2020-01-30 10:57   ` [dpdk-dev] [PATCH v2 0/4] " Luca Boccassi
2020-01-30 16:00 ` [dpdk-dev] [PATCH v3 " David Marchand
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 1/4] hash: fix meson headers packaging David Marchand
2020-01-30 18:01     ` Wang, Yipeng1
2020-01-30 18:40       ` Honnappa Nagarahalli
2020-02-05 19:51         ` Wang, Yipeng1
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 2/4] build: split build helper David Marchand
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 3/4] build: test meson installation David Marchand
2020-01-30 22:17     ` Thomas Monjalon
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 4/4] add ABI checks David Marchand
2020-01-30 22:32     ` Thomas Monjalon
2020-02-01 15:29       ` David Marchand
2020-01-30 22:44     ` Thomas Monjalon
2020-02-02 21:08 ` [dpdk-dev] [PATCH v4 0/3] " David Marchand
2020-02-02 21:08   ` [dpdk-dev] [PATCH v4 1/3] hash: fix meson headers packaging David Marchand
2020-02-05 19:53     ` Wang, Yipeng1
2020-02-02 21:08   ` [dpdk-dev] [PATCH v4 2/3] build: split build helper David Marchand
2020-02-02 21:08   ` [dpdk-dev] [PATCH v4 3/3] add ABI checks David Marchand
2020-02-05 14:13   ` [dpdk-dev] [PATCH v4 0/3] " Thomas Monjalon

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