On Wed, Feb 19, 2020 at 8:56 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > On 2/19/20 1:42 AM, Yonghong Song wrote: > > The latest llvm supports cpu version v3, which is cpu version v1 > > plus some additional 64bit jmp insns and 32bit jmp insn support. > > > > In selftests/bpf Makefile, the llvm flag -mcpu=probe did runtime > > probe into the host system. Depending on compilation environments, > > it is possible that runtime probe may fail, e.g., due to > > memlock issue. This will cause generated code with cpu version v1. > > But those are tiny BPF progs that LLVM is probing. If memlock is not > sufficient, should it try to bump the limit with the diff needed and > only if that fails as well then it bails out to v1. with hundred parallel clangs running and all stamping on the same rlimit I don't think bumping that limit can work. Also building on older kernel should still do v3, since build should produce selftest binaries for the same vmlinux as this kernel tree. We hit this issue with github/libbpf CI. The vm used to do the build was too old. So far we cannot build vmlinux out of latest tree, boot into it and only then build selftests inside. It's too complex for CI system. So we build vmlinux and build selftests in that CI's VM, and then boot into it and run selftests. Upgrading VM is an easy fix for now, but the issue will cause the problems later. So imo fixing selftests build to predictable -mcpu=v3 is the most sensible way.
