cpu: Stop extracting inst_flags from the machInst.

The instruction representation is already encoded in the trace
protobuf, so there's no reason to encode a part of it again. This is
especially true since this supposedly generic code is extracting the
first 8 bits of the machInst, a totally arbitrary set of bits for most
ISAs. If certain bits within a machine instruction are actually
relevant, the consumer of the trace should be able to interpret the
instruction bytes which are already there and extract the same bits
within the context of whatever ISA they're appropriate for.

Change-Id: Idaebe6a110d7d4812c3d7c434582d5a9470bcec1
Reviewed-on: https://gem5-review.googlesource.com/9401
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

cpu: Proposed fix for backwards compatibility in proto/inst.proto.

I haven't tested this at all, but this may fix backwards compatibility
in inst.proto by removing the oneof construct.

Change-Id: Iba19744791c2c577c3b442402f8cc6dcef8550bd
Reviewed-on: https://gem5-review.googlesource.com/9361
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

cpu: Make the protobuf inst tracer accept variable sized instructions.

This change adds an inst_bytes field which is of type bytes, and puts
it in a oneof with the previously required inst field. If an
instruction's encoding happens to be 4 bytes long, the original inst
field will be used. Otherwise, the new variably sized inst_bytes field
will be used.

Because this tracer doesn't have visibility into how the data in
inst_bytes is structured, it can't do any endian conversion itself.
To maintain compatibility between producers and consumers who may have
different endiannesses, all data should be manually converted to
little endian before being stored in this field.

inst will be converted into little endian by protobuf, and so
compatibility doesn't have to be handled manually.

Change-Id: I290713f70e7124d8aa9550c022c71334939d84a6
Reviewed-on: https://gem5-review.googlesource.com/7561
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

proto: Fix warnings for protoc v3

protoc v3 introduces a new syntax for proto files and warns when the
syntax is not explicitly stated.

protoc relies on the fact that undefined preprocessor symbols are
explanded to 0 but since we use -Wundef they end up generating
warnings.

Change-Id: If07abeb54e932469c8f2c4d38634a97fdae40f77
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>

cpu: add support for outputing a protobuf formatted CPU trace

Doesn't support x86 due to static instruction representation.