Hi Peter/Eric, Shall we use atomic_add_return() unconditionally and add some comments? Or I missed something.
Thanks, Shaokun On 2020/1/20 16:18, Peter Zijlstra wrote: > On Fri, Jan 17, 2020 at 10:48:19AM -0800, Eric Dumazet wrote: >> >> >> On 1/17/20 10:38 AM, Arvind Sankar wrote: >>> On Fri, Jan 17, 2020 at 10:16:45AM -0800, Eric Dumazet wrote: >>>> Wasńt it the case back in 2016 already for linux-4.8 ? >>>> >>>> What will prevent someone to send another report to netdev/lkml ? >>>> >>>> -fno-strict-overflow support is not a prereq for CONFIG_UBSAN. >>>> >>>> Fact that we kept in lib/ubsan.c and lib/test_ubsan.c code for >>>> test_ubsan_add_overflow() and test_ubsan_sub_overflow() is disturbing. >>>> >>> >>> No, it was bumped in 2018 in commit cafa0010cd51 ("Raise the minimum >>> required gcc version to 4.6"). That raised it from 3.2 -> 4.6. >>> >> >> This seems good to me, for gcc at least. >> >> Maybe it is time to enfore -fno-strict-overflow in KBUILD_CFLAGS >> instead of making it conditional. > > IIRC there was a bug in UBSAN vs -fwrapv/-fno-strict-overflow that was > only fixed in gcc-8 or 9 or so. > > So while the -fwrapv/-fno-strict-overflow flag has been correctly > supported since like forever, UBSAN was buggy until quite recent when > used in conjustion with that flag. > > . >