I did some bisecting and it seems that the update to clang 10 broke valgrind. Specifically /usr/local/lib/valgrind/memcheck-amd64-openbsd:
$ ktrace -i /usr/local/lib/valgrind/memcheck-amd64-openbsd Abort trap $ kdump 12913 ktrace RET ktrace 0 12913 ktrace CALL execve(0x7f7ffffc6fca,0x7f7ffffc6e68,0x7f7ffffc6e78) 12913 ktrace NAMI "/usr/local/lib/valgrind/memcheck-amd64-openbsd" 12913 ktrace ARGS [0] = "/usr/local/lib/valgrind/memcheck-amd64-openbsd" Compiling valgrind with CC=gcc gives the same result, so my guess is that the linker does something unexpected. martijn@