On Thu, Oct 08, 2020 at 12:04:55PM +0200, Ilya Maximets wrote: > On 10/8/20 11:13 AM, Ilya Maximets wrote: > > On 10/8/20 1:15 AM, Luc Van Oostenryck wrote: > >> On Wed, Oct 07, 2020 at 01:52:34PM +0200, Ilya Maximets wrote: > >>> The actual code in question that makes sparse fail > >>> OVS build could be found here: > >>> https://github.com/openvswitch/ovs/blob/39fbd2c3f0392811689ec780f09baf90faceb877/lib/netdev-linux.c#L1238 > >> > >> I'm impressed and surprised you're using of includes just for Sparse. > >> I also see that this is since 2011. Just for my curiosity, have > >> you an idea for why exactly this was needed and if it is still > >> really needed? > > > > There are some Sparse-related headers that could be safely removed now > > because required functionality is already supported by Sparse. We need > > to clean this up someday, e.g. OVS builds fine without > > include/sparse/threads.h since Sparse 0.5.1. > > > > However, there are headers that are necessary for successful build. > > There are few classes of issues that these headers are targeted on: > > > > 1. Missing functionality in Sparse. > > For example, it doesn't know about __builtin_ia32_pause, so we have to have > > include/sparse/xmmintrin.h. > > Sparse also doesn't know __atomic_load_n that comes from some DPDK headers. > > OVS itself avoids using builtin atomics if __CHECKER__ defined. > > DPDK library also has some issues with types in __sync_add_and_fetch, but I > > do not remember exact problem. We have include/sparse/rte_atomic.h for it. > > These are from the top of my head. I could go through our specific headers > > and make a list of missing features someday if you're interested. OK, I see. I'll add __builtin_ia32_pause() now and I'll look at __atomic_load_n(), __sync_add_and_fetch() and friends soon. > > 2. Sparse complains on standard libraries. > > Complains on PTHREAD_MUTEX_INITIALIZER: > > error: Using plain integer as NULL pointer > > So, we have to have include/sparse/pthread.h. > > Maybe some other examples, but I do not remember right now. > > > > 3. Issues inside external libraries. > > Ex. numa.h header from libnuma contains non-ANSI function declarations. > > So we have include/sparse/numa.h. It's always possible to use -Wno-non-pointer-null and -Wno-old_-style-definition but ... > > 4. Issues with restricted types (these are heaviest). > > OVS uses restricted types like 'ovs_be32' inside (with __attribute__((bitwise))), > > but standard functions like htonl() operates with usual 'uint32_t'. While it's > > safe to use these exact functions, Sparse complains about type mismatch. One > > option here is to explicitly cast arguments with (OVS_FORCE ovs_be32) each time, > > but that is impractical (too many occurrences, ~4K lines of code only for hton/ntoh > > conversions) and will make code less readable. Much easier to override these > > functions just for Sparse. Ex. include/sparse/netinet/in.h. > > > > Similar issue with some data types that goes from external libraries and system > > headers. e.g. DPDK library operates with its own types like rte_be32_t. While > > it's completely safe to mix them with ovs_be32, Sparse doesn't know about that, > > because DPDK doesn't mark them as bitwise. This issue might be fixed on DPDK > > side, I guess. But Sparse will complain about different types even if these types > > defined in exactly same way. e.g. following test fails: > > > > diff --git a/validation/bitwise-cast.c b/validation/bitwise-cast.c > > index 0583461c..9284bd05 100644 > > --- a/validation/bitwise-cast.c > > +++ b/validation/bitwise-cast.c > > @@ -35,6 +35,18 @@ static __be32 quuy(void) > > return (__attribute__((force)) __be32) 1730; > > } > > > > +/* Implicit casts of equally defined types, should be legal? */ > > I do understand why this is illegal. Otherwise it will be not possible to > create le and be types. However, since the main purpose of 'bitwise' attribute, > AFAIU, is to create le and be types, maybe it make sense to have 2 different > attributes? e.g. 'bitwise_le' and 'bitwise_be'. This way Sparse will be able > to detect that 2 different types ovs_be32 and rte_be32_t could be safely mixed, > if both defined with attribute 'bitwise_be' and has same base type uint32_t. Well, one of the key characteristic of __bitwise is that it creates new, distinct, incompatible types and it is very much used as such. For example, in the kernel the 6 {be,le}{16,32,64} are maybe the most used but there are about 100 other bitwise types that are defined (like poll_t or pci_power_t) just to have a distinct type. So, for the problem with rte_be32_t & ovs_be32, the solutions should be to have a common definition, either via a macro or a typedef. Not an easy thing with external libraries. Best regards, -- Luc
