[lldb] [Process/NetBSD] Fix error handling in register operations

[mgorny]

Summary

Ensure that errors are passed through correctly when performing
register read/write operations. Currently, any ptrace() errors are
silently discarded and LLDB behaves as if operation was successful.

// NB: This is a prerequisite for xstate support since xstate might not be supported on old kernels and ptrace() will fail then.

lldb/source/Plugins/Process/NetBSD/NativeRegisterContextNetBSD_x86_64.h

private:
 
   // Private member variables.
   struct reg m_gpr_x86_64;
   struct fpreg m_fpr_x86_64;
   struct dbreg m_dbr_x86_64;
 
   int GetSetForNativeRegNum(int reg_num) const;
 
-  int ReadRegisterSet(uint32_t set);
-  int WriteRegisterSet(uint32_t set);
+  Status ReadRegisterSet(uint32_t set);
+  Status WriteRegisterSet(uint32_t set);
 };
 
 } // namespace process_netbsd
 } // namespace lldb_private
 
 #endif // #ifndef lldb_NativeRegisterContextNetBSD_x86_64_h
 
 #endif // defined(__x86_64__)

lldb/source/Plugins/Process/NetBSD/NativeRegisterContextNetBSD_x86_64.cpp

int NativeRegisterContextNetBSD_x86_64::GetSetForNativeRegNum(
   else if (reg_num <= k_last_mpxc_x86_64)
     return -1; // MPXC
   else if (reg_num <= lldb_dr7_x86_64)
     return DBRegSet; // DBR
   else
     return -1;
 }
 
-int NativeRegisterContextNetBSD_x86_64::ReadRegisterSet(uint32_t set) {
+Status NativeRegisterContextNetBSD_x86_64::ReadRegisterSet(uint32_t set) {
   switch (set) {
   case GPRegSet:
-    ReadGPR();
-    return 0;
+    return ReadGPR();
   case FPRegSet:
-    ReadFPR();
-    return 0;
+    return ReadFPR();
   case DBRegSet:
-    ReadDBR();
-    return 0;
-  default:
-    break;
+    return ReadDBR();
   }
-  return -1;
+  llvm_unreachable("NativeRegisterContextNetBSD_x86_64::ReadRegisterSet");
 }
-int NativeRegisterContextNetBSD_x86_64::WriteRegisterSet(uint32_t set) {
+
+Status NativeRegisterContextNetBSD_x86_64::WriteRegisterSet(uint32_t set) {
   switch (set) {
   case GPRegSet:
-    WriteGPR();
-    return 0;
+    return WriteGPR();
   case FPRegSet:
-    WriteFPR();
-    return 0;
+    return WriteFPR();
   case DBRegSet:
-    WriteDBR();
-    return 0;
-  default:
-    break;
+    return WriteDBR();
   }
-  return -1;
+  llvm_unreachable("NativeRegisterContextNetBSD_x86_64::WriteRegisterSet");
 }
 
 Status
 NativeRegisterContextNetBSD_x86_64::ReadRegister(const RegisterInfo *reg_info,
                                                  RegisterValue &reg_value) {
   Status error;
 
   if (!reg_info) {
NativeRegisterContextNetBSD_x86_64::ReadRegister(const RegisterInfo *reg_info,
   if (set == -1) {
     // This is likely an internal register for lldb use only and should not be
     // directly queried.
     error.SetErrorStringWithFormat("register \"%s\" is in unrecognized set",
                                    reg_info->name);
     return error;
   }
 
-  if (ReadRegisterSet(set) != 0) {
-    // This is likely an internal register for lldb use only and should not be
-    // directly queried.
-    error.SetErrorStringWithFormat(
-        "reading register set for register \"%s\" failed", reg_info->name);
+  error = ReadRegisterSet(set);
+  if (error.Fail())
     return error;
-  }
 
   switch (reg) {
   case lldb_rax_x86_64:
     reg_value = (uint64_t)m_gpr_x86_64.regs[_REG_RAX];
     break;
   case lldb_rbx_x86_64:
     reg_value = (uint64_t)m_gpr_x86_64.regs[_REG_RBX];
     break;
Status NativeRegisterContextNetBSD_x86_64::WriteRegister(
   if (set == -1) {
     // This is likely an internal register for lldb use only and should not be
     // directly queried.
     error.SetErrorStringWithFormat("register \"%s\" is in unrecognized set",
                                    reg_info->name);
     return error;
   }
 
-  if (ReadRegisterSet(set) != 0) {
-    // This is likely an internal register for lldb use only and should not be
-    // directly queried.
-    error.SetErrorStringWithFormat(
-        "reading register set for register \"%s\" failed", reg_info->name);
+  error = ReadRegisterSet(set);
+  if (error.Fail())
     return error;
-  }
 
   switch (reg) {
   case lldb_rax_x86_64:
     m_gpr_x86_64.regs[_REG_RAX] = reg_value.GetAsUInt64();
     break;
   case lldb_rbx_x86_64:
     m_gpr_x86_64.regs[_REG_RBX] = reg_value.GetAsUInt64();
     break;
Status NativeRegisterContextNetBSD_x86_64::WriteRegister(
   case lldb_dr4_x86_64:
   case lldb_dr5_x86_64:
   case lldb_dr6_x86_64:
   case lldb_dr7_x86_64:
     m_dbr_x86_64.dr[reg - lldb_dr0_x86_64] = reg_value.GetAsUInt64();
     break;
   }
 
-  if (WriteRegisterSet(set) != 0)
-    error.SetErrorStringWithFormat("failed to write register set");
-
-  return error;
+  return WriteRegisterSet(set);
 }
 
 Status NativeRegisterContextNetBSD_x86_64::ReadAllRegisterValues(
     lldb::DataBufferSP &data_sp) {
   Status error;
 
   data_sp.reset(new DataBufferHeap(REG_CONTEXT_SIZE, 0));
   if (!data_sp) {