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

H. Peter Anvin
2007-11-29T18:23:58Z

Chuck Ebbert wrote:
> On 11/29/2007 01:09 PM, Linus Torvalds 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?
>> No, %gs is untouched by the kernel, so it contains user space version, and
>> getting the value directly from %gs looks correct.
>>
>
> But this is x86_64, where swapgs is done on kernel entry.
>

For i386-x86_64 sharing, getting to the user segments probably should be
macroized. I'm thinking something like
get_user_[cs|ds|es|fs|gs|ss](thread) in <asm/processor.h> doing the
appropriate thing for different configurations.

-hpa