Re: Compat 32-bit syscall entry from 64-bit task!?

[H.J. Lu]

On Wed, Feb 8, 2012 at 8:29 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 02/08/2012 08:20 PM, Indan Zupancic wrote:
>>
>> CS is already available to user space, but any other value than 0x23 or 0x33
>> will confuse user space, as that is all they know about. Apparently Xen uses
>> different values, but if those are static then user space can check for them
>> separately. But if the values change dynamically then some other way may be
>> needed.
>>
>> But does it make much sense to pass the CPU mode of user space if that mode
>> can be changed at any moment? I don't think it really does. Can you give an
>> example of how that info can be used by a ptracer?
>>
>
> Uh... you could make THAT argument about ANY register state!
>
> I believe H.J. can fill you in about the usage.
>

GDB uses CS value to tell ia32 process from x86-64 process.
At minimum, we need a bit in CS for GDB.  But any changes
will break old GDB.

H.J.
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