From 891e7fb179daec94b56e4a740f645e8685dee8e5 Mon Sep 17 00:00:00 2001 From: Mike Frysinger Date: Mon, 14 Feb 2011 04:58:12 +0000 Subject: [PATCH] sim: change to 64bit time keeping to avoid 32bit overflows The sim-events code jumps through some hoops to avoid using 64bit math to manage the current time. One fundamental assumption here is that by constantly scheduling the sim poll event a short time into the future, the 64bit difference will always fall into a signed 32bit value. This does work most of the time, except for when processing the sim poll event itself. Normally, sim_events_process() will dequeue the sim poll event, update the current time (time_from_event) according to the next pending event, process the sim poll event (which will then requeue the sim poll event), and then continue on. The problem here of course is that the current time is updated in that small window before the sim poll event gets a chance to reschedule itself. So if the 64bit difference between the current time and the next event does not fit into the signed 32bit value, time_from_event overflows, and the internal assert at the end of update_time_from_event() triggers. Since attempts at tweaking sim_events_process() logic introduced other subtle bugs (due to tangled assumptions between most pieces of the sim time keeping code), change the time_from_event to a real 64bit value. Tests on my system between a 32bit ELF and a 64bit ELF show no practical difference (it's all lost in the system noise). Basically, I booted a Linux kernel to userspace and then paniced it; this gave me a constant sample size of about 18 million insns. This was noticed when simulating Blackfin Das U-Boot. The simulated core timer is given the max unsigned timeout value possible on a 32bit processor (0xffffffff). This timeout value is used directly to schedule a hw event in the sim future (the IRQ firing). Once the sim poll event is kicked off, the next pending event is the core timer event which is more than 2^31 ticks in the future, and the sim aborts with: sim-events.c:435: assertion failed - current_time == sim_events_time (sd) Signed-off-by: Mike Frysinger --- sim/common/ChangeLog | 4 ++++ sim/common/sim-events.h | 2 +- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/sim/common/ChangeLog b/sim/common/ChangeLog index 7add3c4d1cf..a2539379f64 100644 --- a/sim/common/ChangeLog +++ b/sim/common/ChangeLog @@ -1,3 +1,7 @@ +2011-02-13 Mike Frysinger + + * sim-events.h (_sim_events.time_from_event): Change type to signed64. + 2011-01-12 Mike Frysinger * sim-hw.c (sim_hw_uninstall): Uncomment hw_tree_delete. diff --git a/sim/common/sim-events.h b/sim/common/sim-events.h index 7303a8ec43d..d3eefb783cc 100644 --- a/sim/common/sim-events.h +++ b/sim/common/sim-events.h @@ -93,7 +93,7 @@ struct _sim_events { unsigned long elapsed_wallclock; SIM_ELAPSED_TIME resume_wallclock; signed64 time_of_event; - int time_from_event; + signed64 time_from_event; int trace; }; -- 2.30.2