* Zachary Amsden ([email protected]) wrote:
> ENTRY(sysenter_entry)
> movl TSS_sysenter_esp0(%esp),%esp
> sysenter_past_esp:
> STI
> pushl $(__USER_DS)
> pushl %ebp
> pushfl
> pushl $(__USER_CS)
> pushl $SYSENTER_RETURN
>
> SYSENTER_RETURN is a link time constant that is defined based on the
> location of the vsyscall page. If the vsyscall page can move, this can
> not be a constant. The reason is, this "fake" exception frame is used
> to return back to the EIP of the call site, and sysenter does not record
> the EIP of the call site.
It's only real issue for something like execshield. For this it's easy
to do the fixed math since it's still at fixed address.
+ DEFINE(VSYSCALL_BASE, (PAGE_OFFSET - 2*PAGE_SIZE));
But execshield has to make SYSENTER_RETURN context sensitive to current
since the vdso is mapped at random location.
thanks,
-chris
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