On Thu, 2008-05-15 at 19:25 -0700, Eric W. Biederman wrote: > "Huang, Ying" <ying.huang at intel.com> writes: > > > On Thu, 2008-05-15 at 11:39 -0700, Eric W. Biederman wrote: > > [...] > >> 2) After we figure out our address read the stack pointer from > >> a fixed location and simply set it. (This is my preference) > > > > Just for confirmation (My English is poor). > > > > Do you mean that kernel A just read the stack top as re-entry point, > > regardless of whether it is return address or argument 1? > > What I was thinking was: > > In kernel A() > > relocate_new_kernel: > > ... > > call *%eax > > kexec_jump_back_entry: > /* This code should be PIC so figure out where we are */ > call 1f > 1: > popl %edi > subl $(1b - relocate_kernel), %edi > > /* Setup a safe stack */ > leal PAGE_SIZE(%edi), %esp > ... > > > Then in purgatory we can read the address of kexec_jump_back_entry > by examining 0(%esp) and export it in whatever fashion is sane. > > However we reach kexec_jump_back_entry we should be fine. I think it is reasonable to enable jumping back and forth more than one time. So the following should be possible: 1. Jump from A to B (actually jump to purgatory, trigger the boot of B) 2. Jump from B to A 3. Jump from A to B again (jump to the kexec_jump_back_entry of B) 4. Jump from B to A ... So it should be possible to get the re-entry point of kernel B in kexec_jump_back_entry of kernel A too. So I think in kexec_jump_back_entry, the caller's stack should be checked to get re-entry point of peer. And the stack state is different depend on where come from, from relocate_new_kernel() or return. Best Regards, Huang Ying
