Samba has a bunch of dependencies on packages like tdb/talloc which currently do not build on ARM64.

https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8933604242952626400

tdb-1.3.15: >>> Emerging (1 of 1) sys-libs/tdb-1.3.15::portage-stable for /build/kevin64/
tdb-1.3.15:  * tdb-1.3.15.tar.gz BLAKE2B SHA512 size ;-) ...                         [ ok ]
tdb-1.3.15:  * Running stacked hooks for pre_pkg_setup
tdb-1.3.15:  *    sysroot_build_bin_dir ...
tdb-1.3.15:  [ ok ]
tdb-1.3.15:  * Running stacked hooks for post_pkg_setup
tdb-1.3.15:  *    python_eclass_hack ...
tdb-1.3.15:  [ ok ]
tdb-1.3.15:  * Running stacked hooks for pre_src_unpack
tdb-1.3.15:  *    python_multilib_setup ...
tdb-1.3.15:  [ ok ]
tdb-1.3.15: >>> Unpacking source...
tdb-1.3.15: >>> Unpacking tdb-1.3.15.tar.gz to /build/kevin64/tmp/portage/sys-libs/tdb-1.3.15/work
tdb-1.3.15: >>> Source unpacked in /build/kevin64/tmp/portage/sys-libs/tdb-1.3.15/work
tdb-1.3.15:  * Running stacked hooks for post_src_unpack
tdb-1.3.15:  *    asan_init ...
tdb-1.3.15:  [ ok ]
tdb-1.3.15:  * Running stacked hooks for pre_src_prepare
tdb-1.3.15:  *    cross ...
tdb-1.3.15:  * ERROR: sys-libs/tdb-1.3.15::portage-stable failed (prepare phase):
tdb-1.3.15:  *   tdb-1.3.15 does not support cross-compiling for arm64
tdb-1.3.15:  * 
tdb-1.3.15:  * Call stack:
tdb-1.3.15:  *        ebuild.sh, line  133:  Called pre_src_prepare
tdb-1.3.15:  *      environment, line 2024:  Called cros_stack_hooks 'pre_src_prepare'
tdb-1.3.15:  *   profile.bashrc, line   86:  Called cros_pre_src_prepare_cross
tdb-1.3.15:  *       tdb.bashrc, line   22:  Called die
tdb-1.3.15:  * The specific snippet of code:
tdb-1.3.15:  *   			die "${P} does not support cross-compiling for ${ARCH}"

To repro:

$ ./setup_board --board=kevin64
$ emerge-kevin64 net-fs/samba