need some clarifications concerning rootf mounting

[stl]

I have dug a little more, and if I well understand, the
initramfs_data.cpio.gz should be
expanded from __initramfs_start (defined in vmlinux.lds.S)

But when and how is it done?
And by who?
Architecture specific code? bootloader, or setup_arch() memory
initialisation function?
Or the kernel itself and automatically during kernel build? Or during boot?

In my case, the initramfs_data.cpio.gz is not present at __initramfs_start.
When the kernel tries to find the compression magic number
("decompress_method() function),
it complains and panic with the following message:

kernel panic: junk in compressed archive

(I precise that I am porting Linux-2.6.37 to a new architecture)

Thanks in advance for your help and advices.
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