Ok, there are no changes between 4.1 and 4.2 (actually, between 4.1 and
4.2.8) re. either the earlycpio or the initramfs loaders.
So, the problem lies elsewhere.
That said, since I bothered to research this:
EARLY cpio loader (lib/earlycpio.c, loads the microcode data): always
skips zero DWORDs (4 bytes) before any cpio header, so it will just
concatenate every non-compressed cpio archive and skip any dword-aligned
zero padding before, after, or between cpio archive headers. There is
one header per file/directory inside the cpio archive.
Note: the early cpio loader does not care for subdirectories, it can
find data by the whole path, and that's how microcode is loaded. This
means the cpio archive with microcode does not need to have any of the
subdirectories inside, it doesn't matter to the kernel.
LATE cpio loader (init/initramfs.c, loads the real initramfs):
1. Skips any zero bytes before the compressed or uncompressed data (thus,
skips any padding between cpio archives).
2. Unpacks any compressed or uncompressed cpio archive it finds,
concatenating the contents (thus, it *will* also unpack
the microcode in the first cpio archive, and this file will be available
inside the initramfs).
3. It *depends* on subdirectories being created *first* before any files
inside them. If this is not done, it will ignore the file.
4. It does NOT skip inital zero-padding on the *decompressed* data (i.e. if
you compress a cpio archive, it must not have
any initial zero padding).
5. It skips any zero padding at the end (compressed or not), but the zeros
must *end* at a DWORD boundary.
So, we need more data to debug this. Because the kernel should have been able
to read and unpack that initramfs just fine. The boot log (with the exact error
message) or a better description of exactly where (and how) things went wrong
during the boot would help.
** Changed in: intel-microcode (Ubuntu)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1507443
Title:
intel-microcode seems to result in an invalid initrd
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