[Devel] Re: [PATCH 1/1] fill vdso with syscall32_setup_pages if TIF_IA32 on x86_64

[Serge E. Hallyn]

Quoting Oren Laadan (orenl at cs.columbia.edu):
> 
> 
> Serge E. Hallyn wrote:
> > Quoting Oren Laadan (orenl at cs.columbia.edu):
> >>
> >> Serge E. Hallyn wrote:
> >>> Quoting Oren Laadan (orenl at cs.columbia.edu):
> >>>> Serge E. Hallyn wrote:
> >>>>> Quoting Oren Laadan (orenl at cs.columbia.edu):
> >>>>>> Cool !
> >>>>>>
> >>>>>> So what do we have working now for 64 bit kernel (for 32 bit kernel
> >>>>>> we know it works...):
> >>>>>>
> >>>>>> 	'restart'	checkpointed
> >>>>>> 	 program	  program
> >>>>>> 	----------------------------------------
> >>>>>> 	  64bit		  64bit		-> works
> >>>>>> 	  32bit		  32bit		-> works
> >>>>>>
> >>>>>> 	  64bit		  32bit		-> ?????
> > 
> > s/?????/Rejected/
> > 
> > CKPT_ARCH_ID is of course different for X86_32 than X86_64, so
> > we refuse restart in restore_read_header().
> > 
> > -serge
> > 
> 
> lol ... that's actually funny !
> 
> Anyway, in light of the IRC discussions, here are the cases again:
> 
> 
> original	original	restart		target
> program		kernel		program		kernel
> --------	---------	--------	--------
> 64 bit		64 bit		64 bit		64 bit	  [0] works
> 
> 32 bit		32 bit		32 bit		32 bit	  [0] works
> 32 bit		64 bit		32 bit		64 bit	  [0] works
> 
> 32 bit		32 bit		32 bit		64 bit	  [1]
> 32 bit		64 bit		32 bit		32 bit	  [1]
> 
> 32 bit		any		64 bit		64 bit	  [2]
> 64 bit		64 bit		32 bit		64 bit	  [2]
> 
> [0] The first 3 cases are "homogeneous", with conditions equal at
> checkpoint and restart. AFAIK, they work.
> 
> [1] The next two cases consider 32 bit program, and vary only the
> environment - the kernel may change from 32 to 64 or back. We want
> them to work.
> 
> IIUC, your comment above means that they don't work because the
> CKPT_ARCH_ID is a mismatch. The fix should be trivial - either
> make 'restart' modify it, or make the kernel tolerate it.

Well, you'd think so, but we also check for uts->machine, and want
to eventually check for kernel config, both of which are obviously
different.

After I comment out the obvious offending checks, it still fails to
restart from x8632->x86-64.  I can spend some time next week figuring
out what we're not quite doing right as there shouldn't be a
problem really.  But do we definately want to go out of our way to try
 and mask out the differences in this case, while trying to detect
cpu differences between two x86-32's for instance?

-serge
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