@dalias I git bisected it to this:
https://git.busybox.net/busybox/commit/libbb/dump.c?h=1_37_stable&id=e2287f99fe6f21fd6435ad04340170ad4ba5f6b3
The place where it fails in kernel build is here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firmware/efi/libstub/Makefile.zboot?h=v6.6#n9
I have sent a patch for a testcase that reproduces it to busybox mailing list