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From: Bruce Richardson <bruce.richardson@intel.com>
To: Ferruh Yigit <ferruh.yigit@intel.com>
Cc: Thomas Monjalon <thomas@monjalon.net>,
	dev@dpdk.org, "Ananyev,
	Konstantin" <konstantin.ananyev@intel.com>,
	Akhil Goyal <akhil.goyal@nxp.com>,
	"Trahe, Fiona" <fiona.trahe@intel.com>,
	David Marchand <david.marchand@redhat.com>,
	Anoob Joseph <anoobj@marvell.com>,
	"Kusztal, ArkadiuszX" <arkadiuszx.kusztal@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: Tue, 4 Feb 2020 10:08:32 +0000
Message-ID: <20200204100832.GA637@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <6c630641-d229-daff-92d5-fb80eae4bd16@intel.com>

On Tue, Feb 04, 2020 at 09:56:31AM +0000, Ferruh Yigit wrote:
> On 2/4/2020 9:45 AM, Thomas Monjalon wrote:
> > 04/02/2020 10:19, Ferruh Yigit:
> >> On 2/3/2020 6:40 PM, Thomas Monjalon wrote:
> >>> 03/02/2020 18:40, Ferruh Yigit:
> >>>> 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?
> >>>
> >>> _LIST_MAX is range of value that DPDK can return in the ABI contract.
> >>> So the appplication can rely on the range 0.._LIST_MAX.
> >>>
> >>>> 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.
> >>>
> >>> No, ABI compatibility contract means you can compile your application
> >>> with DPDK 19.11.0 and run it with DPDK 20.02.
> >>> So _LIST_END comes from 19.11 and does not include ChachaPoly.
> >>
> >> That is what I mean, let me try to give a sample.
> >>
> >> DPDK19.11 returns, A=1, B=2, END=3
> >>
> >> Application compiled with DPDK19.11, it will process A, B and ignore anything ">= 3"
> > 
> > No, the application will not ignore anything ">=3" as I explained above,
> > and you blamed the application for it.
> > Nothing in the API says the application must filter value higher than 3,
> > because as of now, values higher than 3 are PMD bug.
> 
> When application compiled, that is the END value, anything bigger than this
> value is not valid, if any application use the return value directly I think it
> is doing something wrong.
> But yes there may be applications relying on library will always send in the
> range. We never communicated this. But we can add comments to clarify this.
> 
I don't think we should do so, as for any function returning an enum by
definition it should never return an out-of-range value. I strongly agree
with the suggestion of versioning the functions so that the ranges seen by
apps are clamped to the expected 19.11 compatible values.

  reply index

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
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 [this message]
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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