mips: Implement readRegOtherThread and setRegOtherThread directly.

These accessors can be implemented as helper functions within MIPS
without having to plumb them through a bunch of common interfaces.
There are a few problems with the way they were implemented which are
carried forward to this new implementation as well. That includes
hiding the register accesses from the ISA parser and therefore the
CPU's dependency tracking, potentially panicing or accessing a non
existent thread based on a possible set of input values, and modifying
register values even if an instruction is being executed speculatively.

Fixing these problems would be fairly involved and require changing how
dependencies are tracked in all the CPUs so that they can act across
threads, and also how registers are handled in the ISA description
itself.

The original implementation just punted on making this work in CPUs
other than the minor CPU (and potentially one or more CPU models that
were not and/or are not in the code base). Where as that implementation
might have paniced if these methods were called, this will attempt to
work, but may have incorrect behavior based on the limitations
described above. I'd consider this an acceptable tradeoff, at least for
the time being.

Change-Id: I94adceafb9812a8641c76ea3518c3285c31baf51
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18435
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

arch: Fix all override related warnings.

Clang has started(?) reporting override related warnings, something gcc
apparently did before, but was disabled in the SConstruct. Rather than
disable the warnings in for clang as well, this change fixes the
warnings. A future change will re-enable the warnings for gcc.

Change-Id: I3cc79e45749b2ae0f9bebb1acadc56a3d3a942da
Reviewed-on: https://gem5-review.googlesource.com/9343
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

alpha,arm,mips,power,riscv,sparc,x86,isa: De-specialize ExecContexts.

The ISA parser used to generate different copies of exec functions
for each exec context class a particular CPU wanted to use. That's
since been changed so that those functions take a pointer to the base
ExecContext, so the code which would generate those extra functions
can be removed, and some functions which used to be templated on an
ExecContext subclass can be untemplated, or minimally less templated.

Now that some functions aren't going to be instantiated multiple times
with different signatures, there are also opportunities to collapse
templates and make many instruction definitions simpler within the
parser. Since those changes will be less mechanical, they're left for
later changes and will probably be done in smaller increments.

Change-Id: I0015307bb02dfb9c60380b56d2a820f12169ebea
Reviewed-on: https://gem5-review.googlesource.com/5381
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch, cpu: Architectural Register structural indexing

Replace the unified register mapping with a structure associating
a class and an index. It is now much easier to know which class of
register the index is referring to. Also, when adding a new class
there is no need to modify existing ones.

Change-Id: I55b3ac80763702aa2cd3ed2cbff0a75ef7620373
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
[ Fix RISCV build issues ]
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2700

arch: Use shared_ptr for all Faults

This patch takes quite a large step in transitioning from the ad-hoc
RefCountingPtr to the c++11 shared_ptr by adopting its use for all
Faults. There are no changes in behaviour, and the code modifications
are mostly just replacing "new" with "make_shared".

arch: teach ISA parser how to split code across files

This patch encompasses several interrelated and interdependent changes
to the ISA generation step. The end goal is to reduce the size of the
generated compilation units for instruction execution and decoding so
that batch compilation can proceed with all CPUs active without
exhausting physical memory.

The ISA parser (src/arch/isa_parser.py) has been improved so that it can
accept 'split [output_type];' directives at the top level of the grammar
and 'split(output_type)' python calls within 'exec {{ ... }}' blocks.
This has the effect of "splitting" the files into smaller compilation
units. I use air-quotes around "splitting" because the files themselves
are not split, but preprocessing directives are inserted to have the same
effect.

Architecturally, the ISA parser has had some changes in how it works.
In general, it emits code sooner. It doesn't generate per-CPU files,
and instead defers to the C preprocessor to create the duplicate copies
for each CPU type. Likewise there are more files emitted and the C
preprocessor does more substitution that used to be done by the ISA parser.

Finally, the build system (SCons) needs to be able to cope with a
dynamic list of source files coming out of the ISA parser. The changes
to the SCons{cript,truct} files support this. In broad strokes, the
targets requested on the command line are hidden from SCons until all
the build dependencies are determined, otherwise it would try, realize
it can't reach the goal, and terminate in failure. Since build steps
(i.e. running the ISA parser) must be taken to determine the file list,
several new build stages have been inserted at the very start of the
build. First, the build dependencies from the ISA parser will be emitted
to arch/$ISA/generated/inc.d, which is then read by a new SCons builder
to finalize the dependencies. (Once inc.d exists, the ISA parser will not
need to be run to complete this step.) Once the dependencies are known,
the 'Environments' are made by the makeEnv() function. This function used
to be called before the build began but now happens during the build.
It is easy to see that this step is quite slow; this is a known issue
and it's important to realize that it was already slow, but there was
no obvious cause to attribute it to since nothing was displayed to the
terminal. Since new steps that used to be performed serially are now in a
potentially-parallel build phase, the pathname handling in the SCons scripts
has been tightened up to deal with chdir() race conditions. In general,
pathnames are computed earlier and more likely to be stored, passed around,
and processed as absolute paths rather than relative paths. In the end,
some of these issues had to be fixed by inserting serializing dependencies
in the build.

Minor note:
For the null ISA, we just provide a dummy inc.d so SCons is never
compelled to try to generate it. While it seems slightly wrong to have
anything in src/arch/*/generated (i.e. a non-generated 'generated' file),
it's by far the simplest solution.

cpu: rename *_DepTag constants to *_Reg_Base

Make these names more meaningful.

Specifically, made these substitutions:

s/FP_Base_DepTag/FP_Reg_Base/g;
s/Ctrl_Base_DepTag/Misc_Reg_Base/g;
s/Max_DepTag/Max_Reg_Index/g;

scons: Add warning for missing declarations

This patch enables warnings for missing declarations. To avoid issues
with SWIG-generated code, the warning is only applied to non-SWIG
code.

GCC: Get everything working with gcc 4.6.1.

And by "everything" I mean all the quick regressions.

Replace curTick global variable with accessor functions.
This step makes it easy to replace the accessor functions
(which still access a global variable) with ones that access
per-thread curTick values.

MIPS: Format the register index constants like the other ISAs.
Also a few more style fixes.

MIPS: Use BitUnions instead of bits() functions and constants.
Also fix style issues in regions around these changes.

get rid of all instances of readTid() and getThreadNum(). Unify and eliminate
redundancies with threadId() as their replacement.

add back in clobbered MIPS fix for g++ 4.2

go back and fix up MIPS copyright headers

Add in files from merge-bare-iron, get them compiling in FS and SE mode

String constant const-ness changes to placate g++ 4.2.
Also some bug fixes in MIPS ISA uncovered by g++ warnings
(Python string compares don't work in C++!).

mips import pt. 1

src/arch/mips/SConscript:
"mips import pt.1".

Started removing "CodeBlock" objects from the mips isa description.

Edit Fetch DPRINT in simple CPU

src/arch/mips/isa/formats/mt.isa:
change copyright to 2006
src/cpu/simple/base.cc:
Only DPRINT NNPC if we are not using ALPHA
src/cpu/static_inst.hh:
Take Out MIPS Specific functions ...

Authorship stuff

Merging in a month of changes

src/arch/isa_parser.py:
Sign extend bit if you read int reg that is greater than default size
src/arch/mips/SConscript:
src/arch/mips/faults.cc:
src/arch/mips/faults.hh:
src/arch/mips/isa/base.isa:
src/arch/mips/isa/bitfields.isa:
src/arch/mips/isa/decoder.isa:
src/arch/mips/isa/formats/basic.isa:
src/arch/mips/isa/formats/branch.isa:
src/arch/mips/isa/formats/formats.isa:
src/arch/mips/isa/formats/fp.isa:
src/arch/mips/isa/formats/int.isa:
src/arch/mips/isa/formats/mem.isa:
src/arch/mips/isa/formats/noop.isa:
src/arch/mips/isa/formats/tlbop.isa:
src/arch/mips/isa/formats/trap.isa:
src/arch/mips/isa/formats/unimp.isa:
src/arch/mips/isa/formats/unknown.isa:
src/arch/mips/isa/formats/util.isa:
src/arch/mips/isa/includes.isa:
src/arch/mips/isa/main.isa:
src/arch/mips/isa/operands.isa:
src/arch/mips/isa_traits.cc:
src/arch/mips/linux/process.cc:
src/arch/mips/linux/process.hh:
src/arch/mips/process.cc:
src/arch/mips/process.hh:
src/arch/mips/regfile/float_regfile.hh:
src/arch/mips/utility.hh:
1 month of changes!
src/arch/mips/isa/formats/control.isa:
control formats
src/arch/mips/isa/formats/mt.isa:
mips mt format
src/arch/mips/utility.cc:
utility functions