stats: Create HDF5 stat files relative to simout

When using the HDF5 stats backend, we currently pass the filename from
the command line straight to the HDF5 library. This behaviour is
different from the expected behaviour when using plain text stat files
where relative paths are resolved relative to simout. This change adds
support for resolving hdf5 paths relative to simout.

Change-Id: I09cb0b7468735e697125eda7f04c5a85725ca8d0
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20508
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

stats: Catch exceptions by const reference

Catching exceptions by value causes -Werror=catch-value= to be
triggered during a build process. This change replaces the values
with const references in the catch blocks.

Change-Id: Iddabb595c5916d8120dcdb08e2c2f36ff21c3c9b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20528
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

stats: Add beta support for HDF5 stat dumps

This changeset add support for stat dumps in the HDF5 file
format. HDF5 is a binary data format that represents data in a
file-system-like balanced tree. It has native support for
N-dimensional arrays and binary data (e.g., frame buffers).

It has the following benefits over traditional text stat files:

* Efficient storage of time series (multiple stat dumps)

* Fast lookup of stats

* Plenty of existing tooling (e.g., Python libraries and graphical
viewers)

* File format can be used to store frame buffers together with
normal stats.

Drawbacks:

* Large startup cost (single stat dump larger than text equivalent)

* Stat dumps are slower than text

Known limitations:

* Distributions and histograms aren't supported.

HDF5 stat output can be enabled using the 'h5' URL scheme when
overriding the stat file name on gem5's command line. The following
parameters are supported:

* chunking (unsigned): Number of time steps to pre-allocate
(default: 10)

* desc (bool): Output stat descriptions (default: True)

* formulas (bool): Output derived stats (default: True)

Example gem5 command line:

./build/ARM/gem5.opt \
--stats-file="h5://stats.h5?desc=False;formulas=False" \
configs/example/fs.py

Example Python stat consumer that computes IPC:
import h5py

f = h5py.File('stats.h5', 'r')
group = f['/system/cpu']
for i, c in zip(group['committedInsts'], group['numCycles']):
print i, c, i / c

Change-Id: I351c6cbff2fb7bef9012f47876ba227ed288975b
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/8121
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>