* Zachary Amsden (zach@xxxxxxxxxx) 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
