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
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