python: Use PyBind11 instead of SWIG for Python wrappers

Use the PyBind11 wrapping infrastructure instead of SWIG to generate
wrappers for functionality that needs to be exported to Python. This
has several benefits:

  * PyBind11 can be redistributed with gem5, which means that we have
    full control of the version used. This avoid a large number of
    hard-to-debug SWIG issues we have seen in the past.

  * PyBind11 doesn't rely on a custom C++ parser, instead it relies on
    wrappers being explicitly declared in C++. The leads to slightly
    more boiler-plate code in manually created wrappers, but doesn't
    doesn't increase the overall code size. A big benefit is that this
    avoids strange compilation errors when SWIG doesn't understand
    modern language features.

  * Unlike SWIG, there is no risk that the wrapper code incorporates
    incorrect type casts (this has happened on numerous occasions in
    the past) since these will result in compile-time errors.

As a part of this change, the mechanism to define exported methods has
been redesigned slightly. New methods can be exported either by
declaring them in the SimObject declaration and decorating them with
the cxxMethod decorator or by adding an instance of
PyBindMethod/PyBindProperty to the cxx_exports class variable. The
decorator has the added benefit of making it possible to add a
docstring and naming the method's parameters.

The new wrappers have the following known issues:

  * Global events can't be memory managed correctly. This was the
    case in SWIG as well.

Change-Id: I88c5a95b6cf6c32fa9e1ad31dfc08b2e8199a763
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Reviewed-by: Andrew Bardsley <andrew.bardsley@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2231
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

3 files changed, 25 insertions, 27 deletions

diff --git a/src/cpu/BaseCPU.py b/src/cpu/BaseCPU.py
index 7b8a615ea..550ba62ac 100644
--- a/src/cpu/BaseCPU.py
+++ b/src/cpu/BaseCPU.py
@@ -43,6 +43,7 @@
 
 import sys
 
+from m5.SimObject import *
 from m5.defines import buildEnv
 from m5.params import *
 from m5.proxy import *
@@ -96,18 +97,16 @@ class BaseCPU(MemObject):
     abstract = True
     cxx_header = "cpu/base.hh"
 
-    @classmethod
-    def export_methods(cls, code):
-        code('''
-    void switchOut();
-    void takeOverFrom(BaseCPU *cpu);
-    bool switchedOut();
-    void flushTLBs();
-    Counter totalInsts();
-    void scheduleInstStop(ThreadID tid, Counter insts, const char *cause);
-    void scheduleLoadStop(ThreadID tid, Counter loads, const char *cause);
-    uint64_t getCurrentInstCount(ThreadID tid);
-''')
+    cxx_exports = [
+        PyBindMethod("switchOut"),
+        PyBindMethod("takeOverFrom"),
+        PyBindMethod("switchedOut"),
+        PyBindMethod("flushTLBs"),
+        PyBindMethod("totalInsts"),
+        PyBindMethod("scheduleInstStop"),
+        PyBindMethod("scheduleLoadStop"),
+        PyBindMethod("getCurrentInstCount"),
+    ]
 
     @classmethod
     def memory_mode(cls):
diff --git a/src/cpu/kvm/BaseKvmCPU.py b/src/cpu/kvm/BaseKvmCPU.py
index cc0b28fe9..cb9bf481a 100644
--- a/src/cpu/kvm/BaseKvmCPU.py
+++ b/src/cpu/kvm/BaseKvmCPU.py
@@ -35,6 +35,7 @@
 #
 # Authors: Andreas Sandberg
 
+from m5.SimObject import *
 from m5.params import *
 from m5.proxy import *
 
@@ -46,11 +47,10 @@ class BaseKvmCPU(BaseCPU):
     cxx_header = "cpu/kvm/base.hh"
     abstract = True
 
-    @classmethod
-    def export_methods(cls, code):
-        code('''
-      void dump() const;
-''')
+    @cxxMethod
+    def dump(self):
+        """Dump the internal state of KVM to standard out."""
+        pass
 
     @classmethod
     def memory_mode(cls):
diff --git a/src/cpu/kvm/X86KvmCPU.py b/src/cpu/kvm/X86KvmCPU.py
index 18a4d3d6f..411db7dbe 100644
--- a/src/cpu/kvm/X86KvmCPU.py
+++ b/src/cpu/kvm/X86KvmCPU.py
@@ -27,21 +27,20 @@
 # Authors: Andreas Sandberg
 
 from m5.params import *
+from m5.SimObject import *
 from BaseKvmCPU import BaseKvmCPU
 
 class X86KvmCPU(BaseKvmCPU):
     type = 'X86KvmCPU'
     cxx_header = "cpu/kvm/x86_cpu.hh"
 
-    @classmethod
-    def export_methods(cls, code):
-        code('''
-      void dumpFpuRegs();
-      void dumpIntRegs();
-      void dumpSpecRegs();
-      void dumpXCRs();
-      void dumpXSave();
-      void dumpVCpuEvents();
-''')
+    cxx_exports = [
+        PyBindMethod("dumpFpuRegs"),
+        PyBindMethod("dumpIntRegs"),
+        PyBindMethod("dumpSpecRegs"),
+        PyBindMethod("dumpXCRs"),
+        PyBindMethod("dumpXSave"),
+        PyBindMethod("dumpVCpuEvents"),
+    ]
 
     useXSave = Param.Bool(True, "Use XSave to synchronize FPU/SIMD registers")