Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [RFC][PATCH 2/4] checkpoint/restart: x86 support | Date | Sat, 9 Aug 2008 00:29:27 +0200 |
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On Friday 08 August 2008, Oren Laadan wrote:
> > It seems weird that you use __u64 members for the registers, but don't > > include r8..r15 in the list. As a consequence, this structure does not > > seem well suited for either x86-32 or x86-64. > > In the context of CR, x86-32 and x86-64 are distinct architectures because > you cannot always migrate from one to the other (though 32->64 is sometimes > possible). Therefore, each architecture can have a separate checkpoint file > format (eg r8..r15 only for x86-64).
So why do you use __u64 members for your 32 bit registers?
> Except for this special case (32 bit running 64 bit), simple conversion can > be done in the kernel if needed, but most conversion between kernel the > format for different kernel versions (should it change) can be done in > user space (eg. with a filter).
The 32bit on 64bit case is quite common on non-x86 architectures, e.g. powerpc or sparc, where 64 bit kernels typically run 32 bit user space.
A particularly interesting case is mixing 32 and 64 bit tasks in a container that you are checkpointing. This is a very realistic scenario, so there may be good arguments for keeping the format identical between the variations of each architecture.
> > I would suggest either using struct pt_regs by reference, or defining > > it so that you can use the same structure for both 32 and 64 bit x86. > > We prefer not to use the kernel structure directly, but an intermediate > structure that can help mitigate subtle incompatibilities issues (between > kernel configurations, versions, and even compiler versions). > > Anyway, either a single structure for both 32 and 64 bit x86, or separate > "struct cr_hdr_cpu{_32,_64}", one for each architecture.
struct pt_regs is part of the kernel ABI, it will not change.
Arnd <><
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