On Thursday 27 December 2012 02:30 PM, Vineet Gupta wrote: > On Friday 16 November 2012 10:28 AM, Al Viro wrote: >>> + ; --------- check for signals/restore-sigmask ------------ >>> + bbit0 r9, TIF_SIGPENDING, chk_next_work >>> + >>> + ; save CALLEE Regs. >>> + ; (i) If this signal causes coredump - full regfile needed >>> + ; (ii) If signal is SIGTRAP/SIGSTOP, task is being traced thus >>> + ; tracer might call PEEKUSR for a CALLEE reg >>> + ; >>> + ; NOTE: SP will grow up by size of CALLEE Reg-File >>> + SAVE_CALLEE_SAVED_USER ; clobbers r12 >>> + >>> + ; save location of saved Callee Regs @ thread_struct->callee >>> + GET_CURR_TASK_FIELD_PTR TASK_THREAD, r10 >>> + st sp, [r10, THREAD_CALLEE_REG] >>> + >>> + bl @do_signal >>> + >>> + ; unwind SP for cheap discard of Callee saved Regs >>> + DISCARD_CALLEE_SAVED_USER >> Uh-oh... And what if tracer wanted to modify callee-saved regs? > > So the solution would be to either unconditionally restore all the 13 callee > regs > - or add additional state (struct thread) where ptrace makes a note that it > wrote > to a callee reg which is used here to conditional-ize the restore. Former is > simpler to do - although it might ill-affect micro-benchmarks such as LMBench > lat_sig. Anyhow correctness comes before optimization.
Havign coded above, I just couldn't accept the anti-optimization here. Is it absolute sin to take a look at current->ptrace != 0 in deciding whether to save/restore the regs. However that won't work for coredump case. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
