The upgraders in util/cpt_upgraders have been able to check the
root.isa element of checkpoints to determine what "the" ISA is for a
simulation, as a quick way to bail out of that particular updater
applies only to specific ISAs. We are moving away from the idea that
there is a single ISA, and so this mechanism will no longer work.
Fortunately, these cpt_upgraders are only relevant for old checkpoints.
If a checkpoint doesn't have a root.isa element inside it at all, we
know (as of this writing) that it is newer than all of these upgraders
and hence they do not apply. Any new upgraders will have to be written
to not rely on the root.isa field which will be removed. If that sort
of field is still needed, it can be added somewhere else in the
hierarchy, perhaps at the system level, or as part of the actual ISA
object.
The simplest way to implement this new behavior is to add a fallback
option when an upgrader looks for root.isa, specifically ''. If the
root.isa element does not exist, the script will get '' back, and this
will not match whatever ISA it's trying to check against. The one even
remotely more complicated script is isa-is-simobject.py which has
several behaviors for different ISAs. In that case, we just explicitly
check for '' and return early if that's what we found.
Jira Issue: https://gem5.atlassian.net/browse/GEM5-1056
Change-Id: Ie78deccb2bac51f38224e62a28dd733cefd63ed7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48883
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
This commit addresses gem5 checkpoints' linear versioning bottleneck.
Since development is distributed across many private trees, there exists
a sort of 'race' for checkpoint version numbers: internally a checkpoint
version may be used but then resynchronizing with the external tree causes
a conflict on that version. This change replaces the linear version number
with a set of unique strings called tags. Now the only conflicts that can
arise are of tag names, where collisions are much easier to avoid.
The checkpoint upgrader (util/cpt_upgrader.py) upgrades the version
representation, as one would expect. Each tag version implements its
upgrader code in a python file in the util/cpt_upgraders directory
rather than adding a function to the upgrader script itself.
The version tags are stored in the 'Globals' section rather than 'root'
(as the version was previously) because 'Globals' gets unserialized
first and can provide a warning before any other unserialization errors
can occur.
