Re: [PATCH x86/mm 6/6] x86-64 ia32 ptrace get/putreg32 current task

Chuck Ebbert
2007-11-29T23:01:53Z

On 11/29/2007 05:21 PM, Roland McGrath wrote:
>>> case offsetof(struct user32, regs.gs):
>>> *val = child->thread.gsindex;
>>> + if (child == current)
>>> + asm("movl %%gs,%0" : "=r" (*val));
>> Won't this return the kernel's GS instead of the user's?
> [...]
>> But this is x86_64, where swapgs is done on kernel entry.
>
> As I understand it, and from what the documentation I have says, swapgs has
> nothing to do with the %gs selector. It affects the "GS base register",
> i.e. the MSR.
>

Yep, I confused the GS selector with the base address in the descriptor.