From 3e626ccf8f38dbda57dd12554a7057d246101d5b Mon Sep 17 00:00:00 2001 From: Ciro Santilli Date: Thu, 31 May 2018 14:57:43 +0100 Subject: [PATCH] disk persistency: gem5 is not persistent --- README.adoc | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/README.adoc b/README.adoc index 44bf8ea..dbe2c4f 100644 --- a/README.adoc +++ b/README.adoc @@ -865,9 +865,12 @@ the disk image gets overwritten by a fresh filesystem and you lose all changes. Remember that if you forcibly turn QEMU off without `sync` or `poweroff` from inside the VM, e.g. by closing the QEMU window, disk changes may not be saved. -Persistency can be turned off by passing the `snapshot` option to `-drive` (not exposed on our scripts). +Persistency can be turned off by: -When booting from <> however without a disk, persistency is lost. +* passing the `snapshot` option to `-drive` (not exposed on our scripts) +* booting from <> with a CPIO instead of with a disk + +gem5 does not write back to the disk image, which is a good thing to keep its reboots deterministic. === Kernel command line parameters @@ -4995,7 +4998,9 @@ Memory access on vanilla seem impossible due to optimizations that QEMU does: ==== gem5 tracing -gem5 also has a tracing mechanism, as documented at: http://www.gem5.org/Trace_Based_Debugging +gem5 unlike QEMU is deterministic by default without needing to replay traces + +But it also provides a tracing mechanism documented at: link:http://www.gem5.org/Trace_Based_Debugging[] to allow easily inspecting certain aspects of the system: .... ./run -a aarch64 -E 'm5 exit' -g -T Exec