arch-arm: Only build ArmCapstoneDisassembler when ISA is arm (#553)

Currently, if the Capstone header file is found in the host system,
scons will try to build the ArmCapstoneDisassembler regardless of the
gem5 target ISA. This is causing problem when the host has Capstone, but
the gem5 target ISA is not arm. Compiling gem5 in this case will cause
errors, e.g., ArmISA and ArmSystem is not found.

This change aims to prevent building the ArmCapstoneDisassembler when
the gem5 target ISA is not arm.

Ref:
[1] The Arm Capstone PR https://github.com/gem5/gem5/pull/494

Change-Id: I1e714d34aec8fe2a2af8cd351536951053a4d8a5

src/arch/arm/tracers/SConscript

@@ -43,7 +43,7 @@ Source('tarmac_tracer.cc', tags='arm isa')
 Source('tarmac_record.cc', tags='arm isa')
 Source('tarmac_record_v8.cc', tags='arm isa')
 
-if env['CONF']['HAVE_CAPSTONE']:
+if env['CONF']['USE_CAPSTONE']:
     SimObject('ArmCapstone.py', sim_objects=['ArmCapstoneDisassembler'],
-              tags=['capstone', 'arm isa'])
-    Source('capstone.cc', tags=['capstone', 'arm isa'])
+              tags=['arm isa'])
+    Source('capstone.cc', tags=['arm isa'])

src/cpu/Kconfig

@@ -27,3 +27,9 @@ config HAVE_CAPSTONE
     def_bool $(HAVE_CAPSTONE)
 
 rsource "kvm/Kconfig"
+
+config USE_CAPSTONE
+    depends on HAVE_CAPSTONE
+    depends on USE_ARM_ISA
+    bool "Use CapstoneDisassembler"
+    default y

src/cpu/SConscript

@@ -115,9 +115,11 @@ Source('simple_thread.cc')
 Source('thread_context.cc')
 Source('thread_state.cc')
 Source('timing_expr.cc')
-SourceLib('capstone', tags='capstone')
-Source('capstone.cc', tags='capstone')
-SimObject('Capstone.py', sim_objects=['CapstoneDisassembler'], tags='capstone')
+
+if env['CONF']['USE_CAPSTONE']:
+    SourceLib('capstone')
+    Source('capstone.cc')
+    SimObject('Capstone.py', sim_objects=['CapstoneDisassembler'])
 
 SimObject('DummyChecker.py', sim_objects=['DummyChecker'])
 Source('checker/cpu.cc')