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. > 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. If we define _LIST_MAX as a bigger value than current _LIST_END, we have some room to add values in between. If (as of now) we don't have _LIST_MAX room, then yes we must version the functions returning the enum. In this case, the proper solution is to implement rte_cryptodev_info_get_v1911() so it filters out RTE_CRYPTO_AEAD_CHACHA20_POLY1305 capability. With this solution, an application compiled with DPDK 19.11 will keep seeing the same range as before, while a 20.02 application could see and use ChachaPoly. This is another proposal that I was expecting from the crypto team, instead of claiming there is no issue (and wasting precious time). > 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. I don't understand what you mean. I think you misunderstood what is ABI compat. > > 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
