On 04/25/2015 at 11:01 PM, Henrique de Moraes Holschuh wrote: > On Sat, Apr 25, 2015, at 17:16, songbird wrote: > >> # cpio -i -v < /boot/initrd.img-3.18.0-trunk-686-pae >> kernel >> kernel/x86 >> kernel/x86/microcode >> kernel/x86/microcode/GenuineIntel.bin >> 22 blocks > > Yeah, well, you have a multi-segment initramfs. There's an > uncompressed cpio archive first with the "early initramfs" (used for > platform firmware such as processor microcode updates and ACPI table > overrides). It is followed by a compressed cpio archive with the rest > of the initramfs contents. > > The Linux kernel definition of an initramfs image is: "one or more > cpio archives, compressed or uncompressed, one after the other. Any > of these cpio archives can be zero-padded to any lenght, as long as > it is a multiple of 4". It only supports a very specific subset of > the possible cpio archive formats, too. > > The kernel doesn't really care if you change compression type, or > alternate compressed and uncompressed while loading the regular > initramfs, but the early initramfs MUST be the first segment, and it > MUST be uncompressed.
Hm. That's informative, thanks. So how does one manually expand such a multi-segment archive, to examine and possibly manipulate its contents? The only method I can think of which seems likely to be effective is to scan through the file for a gzip-or-suchlike header within the file, then 'cat' the remainder of the file out to where gunzip can find it, and proceed from there - but I don't know of any way to do that using standard tools; if I wanted to try it, I'd have to write code for the purpose myself. Presumably appropriate tools do exist, if only within the kernel tree... -- The Wanderer The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. -- George Bernard Shaw
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