On Tue, 7 May 2019 12:57:15 +0000 David Laight <David.Laight@xxxxxxxxxx> wrote: > > Only the INT3 thing needs 'the gap', but the far bigger change here is > > that kernel frames now have a complete pt_regs set and all sorts of > > horrible crap can go away. > > I'm not doubting that generating the 'five register' interrupt stack frame > for faults in kernel space makes life simpler just suggesting that the > 'emulated call' can be done by emulating the 'iret' rather than generating > a gap in the stack. But how would the user put something on the stack? I don't see how emulating an iret helps here. Can you write some pseudo code to explain what you mean. I also believe the gap is only added for kernel->kernel entries. > > > For 32bit 'the gap' happens naturally when building a 5 entry frame. Yes > > it is possible to build a 5 entry frame on top of the old 3 entry one, > > but why bother... > > Presumably there is 'horrid' code to generate the gap in 64bit mode? > (less horrid than 32bit, but still horrid?) > Or does it copy the entire pt_regs into a local stack frame and use > that for the iret? On x86_64, the gap is only done for int3 and nothing else, thus it is much less horrid. That's because x86_64 has a sane pt_regs storage for all exceptions. -- Steve
