[Lldb-commits] [lldb] [lldb][RISCV] Fix return value reading (PR #163931)

[Georgiy Samoylov via lldb-commits]

================
@@ -602,7 +604,104 @@ GetValObjFromFPRegs(Thread &thread, const RegisterContextSP &reg_ctx,
                                           value, ConstString(""));
   }
   // we should never reach this, but if we do, use the integer registers
-  return GetValObjFromIntRegs(thread, reg_ctx, machine, type_flags, byte_size);
+  return GetValObjFromIntRegs(thread, reg_ctx, machine, compiler_type,
+                              byte_size);
+}
+
+static DataExtractor CopyReturnValueToBuffer(ExecutionContext &exe_ctx,
+                                             RegisterValue &a0_reg_value,
+                                             RegisterValue &a1_reg_value,
+                                             const size_t xlen_byte_size,
+                                             const uint32_t byte_size) {
+
+  DataExtractor a0_extractor;
+  DataExtractor a1_extractor;
+
+  // RISC-V ABI stands:
+  // "Aggregates whose total size is no more than XLEN bits
+  // are passed in a register, with the fields laid out as though
+  // they were passed in memory."
+  if (byte_size <= xlen_byte_size) {
+    // value is stored only in a0
+    a0_reg_value.GetData(a0_extractor);
+    // shrink data to byte_size length
+    DataExtractor data{a0_extractor, 0, byte_size};
+    return data;
+  }
+
+  // "Aggregates whose total size is no more than 2×XLEN bits
+  // are passed in a pair of registers;"
+  if (byte_size <= 2 * xlen_byte_size) {
+    // value is stored in a0 and a1 consequently
+    a0_reg_value.GetData(a0_extractor);
+    a1_reg_value.GetData(a1_extractor);
+    a0_extractor.Append(a1_extractor);
+    // shrink data to byte_size length
+    DataExtractor data{a0_extractor, 0, byte_size};
+    return data;
+  }
+
+  // "Aggregates larger than 2×XLEN bits are passed by reference
+  // and are replaced in the argument list with the address"
+  const lldb::addr_t value_addr =
+      a1_reg_value.GetAsUInt64(LLDB_INVALID_ADDRESS, nullptr);
+
+  if (value_addr == LLDB_INVALID_ADDRESS)
+    return DataExtractor{};
+
+  Status error;
+  WritableDataBufferSP data_sp(new DataBufferHeap(byte_size, 0));
+  if (exe_ctx.GetProcessRef().ReadMemory(value_addr, data_sp->GetBytes(),
+                                         byte_size, error) != byte_size ||
+      error.Fail())
+    return DataExtractor{};
+
+  DataExtractor data;
+  data.SetData(data_sp);
+  return data;
----------------
sga-sc wrote:

In this case I can't do it in one line because [DataExtractor constructor](https://lldb.llvm.org/cpp_reference/classlldb__private_1_1DataExtractor.html#aa34edc5c5ac945be4905b6fc33ab2b2a) also needs byte order and address size which I set after return value creation 

https://github.com/llvm/llvm-project/pull/163931