> > Yeah, this is reasonable. You have to be careful that you save and restore > > any registers that might be used by one of the stubs, but they don't use > > FP. > I also thought about not saving FP-regs on each kernel entry. But if you do > this optimization, you need to save / restore FP-regs on switch_to. Also you > need to get the FP-regs when setting up a signal-handler stackframe. And they > have to be restored on sys_(rt_)sigreturn from the values found in the > stackframe. Thanks for the replies. let me understand them. In a SKAS mode UML kernel, the pseudo code of a system call invocation would be like the following.
wait4(); // wait until a user process raises a syscall save_registers(); // copy the user process' registers to UML kernel space execute_syscall(); // execute the syscall in UML kernel context restore_registers(); // copy the user registers back to the user process but, during execute_syscall(), even if its stubs use all the registers and/or it happens to invoke switch_to(), it will happen all in the UML kernel's context. that means the user process's context will be protected by host kernel's context switching mechanism. doesn't it? because the host kernel will automatically save/restore a process' registers when the process is stopped and resumed, all we care about in the above routine should be to get system call parameters from the tracee and save the return value to it. shouldn't it? (again, only for SKAS) Thanks a lot! > As s390 can give me regs and FP-regs in one single ptrace call, I decided to > not do this optimization. Maybe for i386 and x86_64 it would be worth the > cost. > > Bodo > > > > Jeff > ------------------------------------------------------- This SF.Net email is sponsored by Oracle Space Sweepstakes Want to be the first software developer in space? Enter now for the Oracle Space Sweepstakes! http://ads.osdn.com/?ad_idt12&alloc_id344&op=click _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
