The checkpoint plugin watches for writes on the given symbol and logs
the written value and the simulation time to a given output file.
Additionally, a SHA1 hash is computed over all memory locations between
given start and stop symbols.
On x86, virtual memory is disabled while computing the checkpoint hash.
This means the checkpoint plugin in checksumming over physical, not
virtual, address ranges! This can result to unexpected behaviour if
virtual memory is not used for identity paging.
To save checkpoint information to a file, use the Checkpoint constructor
with a given checkpoint symbol and add the plugin to the experiment (flow).
To check checkpoints against an existing file, use the constructor without
memory symbol and do not add the plugin to the experiment. Instead, define
a memory listener "manually" and call the check() function. This approach
was taken as the simplest form of cooperation between experiment and
plugins.
For SHA1 calculation, C code from RFC 3174 is used to prevent depending
on another external library. However, this may not be the fastest or
best code for the task.
TEMPORARY HACK/WORKAROUND:
Since dOSEK uses the highest bit (31) of some pointers for parity and
the checksum plugin reads these (stack) pointers to determine checksum
regions, the plugin currently DISCARDS BIT 31 of pointers used as
dynamic region limits.
This will be replaced in the future by a callback mechanism, which lets
the experiment specify the regions to checksum (called at each checkpoint).
Change-Id: I176eccc34b582bbf13e52b6943191dd20258acc5
