On Thu, May 27, 2021 at 07:37:05AM -0700, Andrii Nakryiko wrote: > > This patch checks for older versions of pahole and only allows > > DEBUG_INFO_BTF_MODULES if pahole supports zero-sized per-cpu structures. > > DEBUG_INFO_BTF is still allowed as a KVM boot test passed with pahole > > Unfortunately this won't work. The problem is that vmlinux BTF is > corrupted, which results in module BTFs to be rejected as well, as > they depend on it. > > But vmlinux BTF corruption makes BPF subsystem completely unusable. So > even though kernel boots, nothing BPF-related works. So we'd need to > add dependency for DEBUG_INFO_BTF on pahole 1.22+. > While bpf usage would be broken, the kernel will boot and the effect should be transparent to any kernel build based on "make oldconfig". CONFIG_DEBUG_INFO_BTF defaults N so if that is forced out, it will be easily missed by a distribution kernel maintainer. Yes, users of BPF will be affected and it may generate bug reports but the fix will be to build with a working pahole. Breaking boot on the other hand is a lot more visible and hacking around this with a non-zero struct size has been shot down. -- Mel Gorman SUSE Labs
