Hi Greg and Sasha,
Please consider applying the following commits to 6.1 (they all picked cleanly for me):
630ae80ea1dd ("tools lib subcmd: Add install target") 77dce6890a2a ("tools lib subcmd: Make install_headers clearer") 5d890591db6b ("tools lib subcmd: Add dependency test to install_headers") 0e43662e61f2 ("tools/resolve_btfids: Use pkg-config to locate libelf") af03299d8536 ("tools/resolve_btfids: Install subcmd headers") 13e07691a16f ("tools/resolve_btfids: Alter how HOSTCC is forced") 56a2df7615fa ("tools/resolve_btfids: Compile resolve_btfids as host program") e0975ab92f24 ("tools/resolve_btfids: Tidy HOST_OVERRIDES") 2531ba0e4ae6 ("tools/resolve_btfids: Pass HOSTCFLAGS as EXTRA_CFLAGS to prepare targets") edd75c802855 ("tools/resolve_btfids: Fix setting HOSTCFLAGS")
The most critical change is 13e07691a16f, which resolves a missing EXTRA_CFLAGS to the libsubcmd build. Without that EXTRA_CFLAGS, the Android hermetic toolchain kernel build fails on host distributions using glibc 2.38 and newer. The majority of those commits are strictly needed due to dependency/fixes requirements, the few that are not still seem to be worth bringing in for ease of backporting the rest and do not appear to cause any problems.
I proposed another solution downstream, which may be more palatable if people have concerns about this list of changes and the risk of regressions, but Ian seemed to have some concerns on that thread around that path and suggested this series of backports instead:
https://android-review.googlesource.com/c/kernel/common/+/2745896
While the number of patches seems large, the final changes are pretty well self-contained.
Cheers, Nathan