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

[Indan Zupancic]

On Fri, January 20, 2012 23:41, H. Peter Anvin wrote:
> On 01/20/2012 02:40 PM, Roland McGrath wrote:
>> If you change the size of a regset, then the new full size will be the size
>> of the core file notes.  Existing userland tools will not be expecting
>> this, they expect a known exact size.  If you need to add new stuff, it
>> really is easier all around to add a new regset flavor.  When adding a new
>> one, you can make it variable-sized from the start so as to be extensible
>> in the future.  We did this for NT_X86_XSTATE, for example.
>>
>
> Yes, that definitely seems cleaner.

I would prefer Linus' way of just stuffing it into cs. Jamie also wanted
a bit telling in what mode the userspace is running. That's 3 bits in total,
with one bit telling whether the other bits are valid or not. Anything else?
Maybe a bit telling whether it is syscall entry or exit?

As all this is very x86_64 specific and cs is already used to figure out
the mode, it seems overkill to add a new regset just for this.

It's a lot easier for existing code to add an extra cs check than to use
different register sets and different ptrace commands. Considering that
PTRACE_GETREGSET is undocumented it's likely that existing code isn't
using it much.

Greetings,

Indan


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/