[Lldb-commits] [lldb] [LLDB] Expose and display GDB remote register union values (PR #224147)

[Greg Clayton via lldb-commits]

================
@@ -161,6 +238,60 @@ class CommandObjectRegisterRead : public CommandObjectParsed {
     return true;
   }
 
+  bool DumpRegisterField(const ExecutionContext &exe_ctx, Stream &strm,
+                         const RegisterInfo &reg_info,
+                         llvm::StringRef expression_path,
+                         size_t reg_name_right_align_at,
+                         CommandReturnObject &result) {
+    if (!llvm::isa_and_present<RegisterTypeComposite>(reg_info.register_type)) {
+      result.AppendErrorWithFormat(
+          "Register '%s' does not have a structured type", reg_info.name);
+      return false;
+    }
+
+    StackFrame *frame = exe_ctx.GetFramePtr();
+    if (!frame)
+      return false;
+    lldb::RegisterContextSP reg_ctx_sp = frame->GetRegisterContextSP();
+    ValueObjectSP register_value =
+        ValueObjectRegister::Create(frame, reg_ctx_sp, &reg_info);
+    ValueObjectSP child =
+        ResolveRegisterExpressionPath(register_value, expression_path);
----------------
clayborg wrote:

We should make a new ValueObjectRegister creator function like:

```
llvm::Expected<ValueObjectSP> 
ValueObjectRegister::CreateFromExpressionPath(
    StackFrame *frame,
    lldb::RegisterContextSP reg_ctx_sp,
    StringRef expression_path);
```
Expression path is always the full path that includes the register name and anything after it. So if the user specifies "x0", it will return a ValueObjectRegister shared pointer to the root register. If it is "u0.f32" or "u0.floats[2]", it will get root ValueObjectRegister and call `ValueObject::GetValueForExpressionPath(...)` where the expression path is relative to the current ValueObject. So we would get the value object for "u0" and call `register_value->GetValueForExpressionPath(".f32", ...)`. This way we can re-use this functionality everywhere in LLDB, not just here.

https://github.com/llvm/llvm-project/pull/224147