I've successfully hibernated and resumed from swap partition in Linux. As far as I know, nothing was since swapped, nor has been the swap partition otherwise modified. That makes me think, that the hibernated image of previous state is still present and functional, only with modified header or something like that.
If that is true, how can I resume from such image? Tangent question is then whether it is advisable to try such thing, and what are some things it could break.
Obvious possibility to get this working is to recreate the process of hibernation but not actually save the image. After misguided fiddling with
/sys/power/resume I came across this segment from https://www.kernel.org/doc/Documentation/power/swsusp.txt:
The resume process checks for the presence of the resume device, if found, it then checks the contents for the hibernation image signature. If both are found, it resumes the hibernation image.
From this I get the feeling, that this signature is what is written at hibernation to signify, that the device needs to be resumed and is wiped afterwards to prevent recurrent resuming. Even if that is true, I'm not skilled enough to get information about the signature from kernel code and hex-dump of swap partition is surprisingly sparse and full of structures I don't understand.