Fix const-correctness in RegisterContext methods, NFC

[vsk]

Summary

A few methods in RegisterContext classes accept const objects which are
cast to a non-const thread_state_t. Drop const-ness more explicitly
where we mean to do so. This fixes a slew of warnings.

[clayborg]

Seems wrong to remove the const on structs that don't need to change in order to make the write happen. Can't we just quiet the warnings with a const_cast inside the function call?

[vsk]

In D40821#945314, @clayborg wrote:

Seems wrong to remove the const on structs that don't need to change in order to make the write happen. Can't we just quiet the warnings with a const_cast inside the function call?

Absolutely. I opted for dropping const to make the DoRead* and DoWrite* methods feel consistent. At first glance, it looked like there may be methods in RegisterContext which expect non-const GPR/FPU/etc objects, so it seemed reasonable to drop const.

I'm open to just adding in the const_cast<X>(static_cast<const X>(...)) pattern as needed to suppress warnings, and to constifying the rest of RegisterContext as a follow-up. Let me know what you'd prefer.

[clayborg]

In D40821#945379, @vsk wrote:

In D40821#945314, @clayborg wrote:

Seems wrong to remove the const on structs that don't need to change in order to make the write happen. Can't we just quiet the warnings with a const_cast inside the function call?

Absolutely. I opted for dropping const to make the DoRead* and DoWrite* methods feel consistent. At first glance, it looked like there may be methods in RegisterContext which expect non-const GPR/FPU/etc objects, so it seemed reasonable to drop const.

I'm open to just adding in the const_cast<X>(static_cast<const X>(...)) pattern as needed to suppress warnings, and to constifying the rest of RegisterContext as a follow-up. Let me know what you'd prefer.

Please do that as it makes more sense API wise.

[vsk]

• Address Greg's comments.

lldb/trunk/source/Plugins/Process/Utility/RegisterContextMach_arm.cpp

 
 int RegisterContextMach_arm::DoReadDBG(lldb::tid_t tid, int flavor, DBG &dbg) {
   mach_msg_type_number_t count = DBGWordCount;
   return ::thread_get_state(tid, flavor, (thread_state_t)&dbg, &count);
 }
 
 int RegisterContextMach_arm::DoWriteGPR(lldb::tid_t tid, int flavor,
                                         const GPR &gpr) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&gpr, GPRWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<GPR *>(&gpr)),
+      GPRWordCount);
 }
 
 int RegisterContextMach_arm::DoWriteFPU(lldb::tid_t tid, int flavor,
                                         const FPU &fpu) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&fpu, FPUWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<FPU *>(&fpu)),
+      FPUWordCount);
 }
 
 int RegisterContextMach_arm::DoWriteEXC(lldb::tid_t tid, int flavor,
                                         const EXC &exc) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&exc, EXCWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<EXC *>(&exc)),
+      EXCWordCount);
 }
 
 int RegisterContextMach_arm::DoWriteDBG(lldb::tid_t tid, int flavor,
                                         const DBG &dbg) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&dbg, DBGWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<DBG *>(&dbg)),
+      DBGWordCount);
 }
 
 #endif

lldb/trunk/source/Plugins/Process/Utility/RegisterContextMach_i386.cpp

 
 int RegisterContextMach_i386::DoReadEXC(lldb::tid_t tid, int flavor, EXC &exc) {
   mach_msg_type_number_t count = EXCWordCount;
   return ::thread_get_state(tid, flavor, (thread_state_t)&exc, &count);
 }
 
 int RegisterContextMach_i386::DoWriteGPR(lldb::tid_t tid, int flavor,
                                          const GPR &gpr) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&gpr, GPRWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<GPR *>(&gpr)),
+      GPRWordCount);
 }
 
 int RegisterContextMach_i386::DoWriteFPU(lldb::tid_t tid, int flavor,
                                          const FPU &fpu) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&fpu, FPUWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<FPU *>(&fpu)),
+      FPUWordCount);
 }
 
 int RegisterContextMach_i386::DoWriteEXC(lldb::tid_t tid, int flavor,
                                          const EXC &exc) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&exc, EXCWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<EXC *>(&exc)),
+      EXCWordCount);
 }
 
 #endif

lldb/trunk/source/Plugins/Process/Utility/RegisterContextMach_x86_64.cpp

 int RegisterContextMach_x86_64::DoReadEXC(lldb::tid_t tid, int flavor,
                                           EXC &exc) {
   mach_msg_type_number_t count = EXCWordCount;
   return ::thread_get_state(tid, flavor, (thread_state_t)&exc, &count);
 }
 
 int RegisterContextMach_x86_64::DoWriteGPR(lldb::tid_t tid, int flavor,
                                            const GPR &gpr) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&gpr, GPRWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<GPR *>(&gpr)),
+      GPRWordCount);
 }
 
 int RegisterContextMach_x86_64::DoWriteFPU(lldb::tid_t tid, int flavor,
                                            const FPU &fpu) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&fpu, FPUWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<FPU *>(&fpu)),
+      FPUWordCount);
 }
 
 int RegisterContextMach_x86_64::DoWriteEXC(lldb::tid_t tid, int flavor,
                                            const EXC &exc) {
-  return ::thread_set_state(tid, flavor, (thread_state_t)&exc, EXCWordCount);
+  return ::thread_set_state(
+      tid, flavor, reinterpret_cast<thread_state_t>(const_cast<EXC *>(&exc)),
+      EXCWordCount);
 }
 
 #endif