packaging/make-sysroot.sh populates a minimal Alpine aarch64 rootfs with
apk-tools-static, so a cross build needs no root, no qemu and no phone. Adapted
from imsd's, plus glib-dev for the bus layer that is coming.
Building against a real Alpine sysroot means the binary links dynamically
against the phone's own musl and libc++ -- libc++, libc++abi, libunwind and
libgcc_s are all already on pmOS. The harness this daemon replaces had to be
built -static, but only because it was built with the host's glibc toolchain;
that constraint was never about the target.
The pipeline is proven end to end rather than assumed: the cross-built binary
runs on the phone, and all five core suites pass there too -- on the real
hardware, not just under qemu-aarch64. That matters for modules that are almost
entirely little-endian field packing and offset arithmetic.
fingerprintd will own the FP6's fingerprint sensor: the rail, the QTEE session,
the storage callbacks QTEE makes back into the normal world, and
net.reactivated.Fprint so pam_fprintd and the desktop need no changes. None of
that runs yet. What is here is the first core module and the machinery around
it.
Fingerprintd:Sfs is the gpfile listener's frame -- the callback that carries
47 of 66 storage requests during an enrolment. It is parse, reply and root
mapping only: no file I/O, no TEE, no allocation of the shared buffer. The
daemon shell supplies those, which is what lets every byte-level decision be
tested on a dev box with no phone.
The module exists mainly to hold one fact. READ answers at req+0x00c and WRITE
reads its payload from req+0x110, because the frame is a union: a WRITE still
needs its path while the payload is copied out, so it sits past the 256-byte
path field, while a READ has consumed the path and packs its reply over it.
Conflating them is wrong in both directions with the same symptom -- the
container does not round-trip, QTEE's HMAC check fails, and the file is
unlinked as tampered on the next session.
So the tests do not assert the constants against themselves. They load two real
containers off the phone -- one written correctly, one written with the offsets
conflated -- and re-derive the bug: the broken one opens with ASCII path text
rather than a binary HMAC, that text is the group name from character 8 because
the read offset is 8 bytes into the path field, and the real container sits
exactly 0x104 further in. Then a write-store-read round trip must be the
identity, and the same round trip through a single offset must not be.
O_TRUNC gets a static_assert of its own. QTEE writes a container as
write(0,4096), write(4096,N), write(0,4096), so truncating on open leaves 4096
bytes where a 258850-byte template belongs; it unlinks a file it means to
shorten rather than relying on the opener.
Verified by mutation: conflating the offsets, making DataOffset return the read
offset for writes, and setting O_TRUNC each fail the suite.
