Daniel Kiper <daniel.kiper at oracle.com> writes: > Hi, > > Could you explain why do you clear all registers just before jumping > into purgatory (please look into arch/x86/kernel/relocate_kernel_64.S > for more details)? There is no any single word about that. I do not > count comment which states what is going on. purgatory on entry does > not assume any value in registers. Are you going to use that feature > for something in the future (e.g. to differentiate between callers > and/or Linux versions if it be needed)? It has been a long time now, but as I recall the reason was to just have things well defined and to make certain that we were not accidentially exporting anything except the stack pointer for applications to depend upon. 0/NULL is a good choice because if you are expecting pointer for some strange reason interesting things happen. purgatory is definitely not the only target and the C version of purgatory was actually written well after kexec came into existence. Is there any particular reason why you are asking? > By the way, interestingly it is not done if preserve_context is in > force. Something different is done, and all of the registers should be preserved from the when the return to Linux. In theory you can swap between to kernels with the preserve_context case. Technically I like the ability but I don't know that it has ever achieved much uptake. Eric
