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. 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. 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? */ +typedef u32 __attribute__((bitwise)) __my_be32_1; +typedef u32 __attribute__((bitwise)) __my_be32_2; + +static __my_be32_1 my_type(void) +{ + __my_be32_2 x = (__attribute__((force)) __my_be32_2) 0x2a; + + return x; +} + + /* * check-name: conversions to bitwise types * check-command: sparse -Wbitwise $file --- bitwise-cast.c:46:16: warning: incorrect type in return expression (different base types) bitwise-cast.c:46:16: expected restricted __my_be32_1 bitwise-cast.c:46:16: got restricted __my_be32_2 [usertype] x This might be not a full list of issues we have, but this is what I can remember right now. Best regards, Ilya Maximets.
