Use C++17 [[fallthrough]] attribute

This changes gdb to use the C++17 [[fallthrough]] attribute rather
than special comments.

This was mostly done by script, but I neglected a few spellings and so
also fixed it up by hand.

I suspect this fixes the bug mentioned below, by switching to a
standard approach that, presumably, clang supports.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=23159
Approved-By: John Baldwin <jhb@FreeBSD.org>
Approved-By: Luis Machado <luis.machado@arm.com>
Approved-By: Pedro Alves <pedro@palves.net>

60 files changed, 140 insertions, 143 deletions

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index eaae2d9..ba37b49 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -1851,7 +1851,7 @@ pass_in_v_vfp_candidate (struct gdbarch *gdbarch, struct regcache *regcache,
       if (arg_type->is_vector ())
 	return pass_in_v (gdbarch, regcache, info, arg_type->length (),
 			  arg->contents ().data ());
-      /* fall through.  */
+      [[fallthrough]];
 
     case TYPE_CODE_STRUCT:
     case TYPE_CODE_UNION:
diff --git a/gdb/ada-exp.y b/gdb/ada-exp.y
index 3280a48..fcb5aa4 100644
--- a/gdb/ada-exp.y
+++ b/gdb/ada-exp.y
@@ -1307,7 +1307,7 @@ write_object_renaming (struct parser_state *par_state,
 	break;
       case 'L':
 	slice_state = LOWER_BOUND;
-	/* FALLTHROUGH */
+	[[fallthrough]];
       case 'S':
 	renaming_expr += 1;
 	if (isdigit (*renaming_expr))
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index ff7222c..1a59156 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -5508,7 +5508,7 @@ compare_names_with_case (const char *string1, const char *string2,
 	  else
 	    return 1;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
     default:
       if (*string2 == '(')
 	return strcmp_iw_ordered (string1, string2);
diff --git a/gdb/ada-valprint.c b/gdb/ada-valprint.c
index 86cab35..309bb51 100644
--- a/gdb/ada-valprint.c
+++ b/gdb/ada-valprint.c
@@ -89,7 +89,7 @@ print_optional_low_bound (struct ui_file *stream, struct type *type,
       break;
     case TYPE_CODE_UNDEF:
       index_type = NULL;
-      /* FALL THROUGH */
+      [[fallthrough]];
     default:
       if (low_bound == 1)
 	return 0;
diff --git a/gdb/amd64-windows-tdep.c b/gdb/amd64-windows-tdep.c
index 9d69ec2..6be4343 100644
--- a/gdb/amd64-windows-tdep.c
+++ b/gdb/amd64-windows-tdep.c
@@ -380,7 +380,7 @@ amd64_windows_return_value (struct gdbarch *gdbarch, struct value *function,
 		break;
 	      }
 	  }
-	/* fall through */
+	[[fallthrough]];
       default:
 	/* All other values that are 1, 2, 4 or 8 bytes long are returned
 	   via RAX.  */
diff --git a/gdb/arch/arm.c b/gdb/arch/arm.c
index 4720c20..6fc4c0e 100644
--- a/gdb/arch/arm.c
+++ b/gdb/arch/arm.c
@@ -153,7 +153,7 @@ arm_instruction_changes_pc (uint32_t this_instr)
 	    return 0;
 	  }
 	/* Data processing instruction.  */
-	/* Fall through.  */
+	[[fallthrough]];
 
       case 0x1:
 	if (bits (this_instr, 12, 15) == 15)
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 7a93b09..23fecf7 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -7600,7 +7600,7 @@ arm_decode_miscellaneous (struct gdbarch *gdbarch, uint32_t insn,
       else if (op == 0x3)
 	/* Not really supported.  */
 	return arm_copy_unmodified (gdbarch, insn, "smc", dsc);
-      /* Fall through.  */
+      [[fallthrough]];
 
     default:
       return arm_copy_undef (gdbarch, insn, dsc);
diff --git a/gdb/c-exp.y b/gdb/c-exp.y
index a27dbfa..2b4c218 100644
--- a/gdb/c-exp.y
+++ b/gdb/c-exp.y
@@ -2731,7 +2731,7 @@ lex_one_token (struct parser_state *par_state, bool *is_quoted_name)
 	  last_was_structop = true;
 	  goto symbol;		/* Nope, must be a symbol. */
 	}
-      /* FALL THRU.  */
+      [[fallthrough]];
 
     case '0':
     case '1':
@@ -2828,7 +2828,7 @@ lex_one_token (struct parser_state *par_state, bool *is_quoted_name)
 	    return ENTRY;
 	  }
       }
-      /* FALLTHRU */
+      [[fallthrough]];
     case '+':
     case '-':
     case '*':
@@ -2855,7 +2855,7 @@ lex_one_token (struct parser_state *par_state, bool *is_quoted_name)
     case 'U':
       if (tokstart[1] != '"' && tokstart[1] != '\'')
 	break;
-      /* Fall through.  */
+      [[fallthrough]];
     case '\'':
     case '"':
 
diff --git a/gdb/cli/cli-setshow.c b/gdb/cli/cli-setshow.c
index c7bbac1..11f9306 100644
--- a/gdb/cli/cli-setshow.c
+++ b/gdb/cli/cli-setshow.c
@@ -379,7 +379,7 @@ do_set_command (const char *arg, int from_tty, struct cmd_list_element *c)
     case var_filename:
       if (*arg == '\0')
 	error_no_arg (_("filename to set it to."));
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case var_optional_filename:
       {
 	char *val = NULL;
diff --git a/gdb/coffread.c b/gdb/coffread.c
index 5898b3a..3736363 100644
--- a/gdb/coffread.c
+++ b/gdb/coffread.c
@@ -896,7 +896,7 @@ coff_symtab_read (minimal_symbol_reader &reader,
 	     backtraces, so filter them out (from phdm@macqel.be).  */
 	  if (within_function)
 	    break;
-	  /* Fall through.  */
+	  [[fallthrough]];
 	case C_STAT:
 	case C_THUMBLABEL:
 	case C_THUMBSTAT:
@@ -934,7 +934,7 @@ coff_symtab_read (minimal_symbol_reader &reader,
 	       that look like this.  Ignore them.  */
 	    break;
 	  /* For static symbols that don't start with '.'...  */
-	  /* Fall through.  */
+	  [[fallthrough]];
 	case C_THUMBEXT:
 	case C_THUMBEXTFUNC:
 	case C_EXT:
diff --git a/gdb/compile/compile-c-support.c b/gdb/compile/compile-c-support.c
index 3a3e4d2..f099504 100644
--- a/gdb/compile/compile-c-support.c
+++ b/gdb/compile/compile-c-support.c
@@ -267,7 +267,7 @@ generate_register_struct (struct ui_file *stream, struct gdbarch *gdbarch,
 		    }
 		}
 
-		/* Fall through.  */
+		[[fallthrough]];
 
 	      default:
 		gdb_printf (stream,
diff --git a/gdb/compile/compile-c-symbols.c b/gdb/compile/compile-c-symbols.c
index 5982178..a80b9a4 100644
--- a/gdb/compile/compile-c-symbols.c
+++ b/gdb/compile/compile-c-symbols.c
@@ -136,7 +136,7 @@ convert_one_symbol (compile_c_instance *context,
 		     "be referenced from the current thread in "
 		     "compiled code."),
 		   sym.symbol->print_name ());
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 	case LOC_UNRESOLVED:
 	  /* 'symbol_name' cannot be used here as that one is used only for
 	     local variables from compile_dwarf_expr_to_c.
diff --git a/gdb/compile/compile-cplus-symbols.c b/gdb/compile/compile-cplus-symbols.c
index 1edbf8f..5cffe5c 100644
--- a/gdb/compile/compile-cplus-symbols.c
+++ b/gdb/compile/compile-cplus-symbols.c
@@ -132,7 +132,7 @@ convert_one_symbol (compile_cplus_instance *instance,
 		     "be referenced from the current thread in "
 		     "compiled code."),
 		   sym.symbol->print_name ());
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 	case LOC_UNRESOLVED:
 	  /* 'symbol_name' cannot be used here as that one is used only for
 	     local variables from compile_dwarf_expr_to_c.
diff --git a/gdb/cp-name-parser.y b/gdb/cp-name-parser.y
index e6c8c4c..9a359d4 100644
--- a/gdb/cp-name-parser.y
+++ b/gdb/cp-name-parser.y
@@ -1604,7 +1604,7 @@ yylex (YYSTYPE *lvalp, cpname_state *state)
 					  sizeof "(anonymous namespace)" - 1);
 	  return NAME;
 	}
-	/* FALL THROUGH */
+	[[fallthrough]];
 
     case ')':
     case ',':
@@ -1641,7 +1641,7 @@ yylex (YYSTYPE *lvalp, cpname_state *state)
 	  state->lexptr++;
 	  return '-';
 	}
-      /* FALL THRU.  */
+      [[fallthrough]];
 
     try_number:
     case '0':
diff --git a/gdb/cp-support.c b/gdb/cp-support.c
index cb16944..9eb5577 100644
--- a/gdb/cp-support.c
+++ b/gdb/cp-support.c
@@ -531,7 +531,7 @@ replace_typedefs (struct demangle_parse_info *info,
 	{
 	case DEMANGLE_COMPONENT_ARGLIST:
 	  check_cv_qualifiers (ret_comp);
-	  /* Fall through */
+	  [[fallthrough]];
 
 	case DEMANGLE_COMPONENT_FUNCTION_TYPE:
 	case DEMANGLE_COMPONENT_TEMPLATE:
diff --git a/gdb/ctfread.c b/gdb/ctfread.c
index c74ec04..03a042e 100644
--- a/gdb/ctfread.c
+++ b/gdb/ctfread.c
@@ -1473,7 +1473,7 @@ ctf_psymtab_type_cb (ctf_id_t tid, void *arg)
     {
       case CTF_K_ENUM:
 	ctf_psymtab_add_enums (ccp, tid);
-	/* FALL THROUGH */
+	[[fallthrough]];
       case CTF_K_STRUCT:
       case CTF_K_UNION:
 	domain = STRUCT_DOMAIN;
diff --git a/gdb/d-exp.y b/gdb/d-exp.y
index 6c5569a..e250798 100644
--- a/gdb/d-exp.y
+++ b/gdb/d-exp.y
@@ -1103,7 +1103,7 @@ lex_one_token (struct parser_state *par_state)
 	    last_was_structop = 1;
 	  goto symbol;		/* Nope, must be a symbol.  */
 	}
-      /* FALL THRU.  */
+      [[fallthrough]];
 
     case '0':
     case '1':
@@ -1180,7 +1180,7 @@ lex_one_token (struct parser_state *par_state)
 	    return ENTRY;
 	  }
       }
-      /* FALLTHRU */
+      [[fallthrough]];
     case '+':
     case '-':
     case '*':
diff --git a/gdb/d-valprint.c b/gdb/d-valprint.c
index 38fb2a0..4c3ea22 100644
--- a/gdb/d-valprint.c
+++ b/gdb/d-valprint.c
@@ -85,7 +85,7 @@ d_value_print_inner (struct value *val, struct ui_file *stream, int recurse,
 				  stream, recurse, val, options);
 	if (ret == 0)
 	  break;
-	/* Fall through.  */
+	[[fallthrough]];
       default:
 	c_value_print_inner (val, stream, recurse, options);
 	break;
diff --git a/gdb/dbxread.c b/gdb/dbxread.c
index b92193b..99d9fba 100644
--- a/gdb/dbxread.c
+++ b/gdb/dbxread.c
@@ -2806,7 +2806,7 @@ process_one_symbol (int type, int desc, CORE_ADDR valu, const char *name,
     case N_NBSTS:
     case N_NBLCS:
       unknown_symtype_complaint (hex_string (type));
-      /* FALLTHROUGH */
+      [[fallthrough]];
 
     define_a_symbol:
       /* These symbol types don't need the address field relocated,
diff --git a/gdb/disasm-selftests.c b/gdb/disasm-selftests.c
index 0cf766a..200d33a 100644
--- a/gdb/disasm-selftests.c
+++ b/gdb/disasm-selftests.c
@@ -126,7 +126,7 @@ get_test_insn (struct gdbarch *gdbarch, size_t *len)
 	if (info->bits_per_address > sizeof (bfd_vma) * CHAR_BIT)
 	  return insn;
       }
-      /* fall through */
+      [[fallthrough]];
     default:
     generic_case:
       {
diff --git a/gdb/dwarf2/macro.c b/gdb/dwarf2/macro.c
index 2e88e67..7d86d16 100644
--- a/gdb/dwarf2/macro.c
+++ b/gdb/dwarf2/macro.c
@@ -784,7 +784,7 @@ dwarf_decode_macro_bytes (dwarf2_per_objfile *per_objfile,
 	      /* We don't recognize any vendor extensions.  */
 	      break;
 	    }
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 
 	default:
 	  mac_ptr = skip_unknown_opcode (macinfo_type, opcode_definitions,
@@ -939,7 +939,7 @@ dwarf_decode_macros (dwarf2_per_objfile *per_objfile,
 	      read_direct_string (abfd, mac_ptr, &bytes_read);
 	      mac_ptr += bytes_read;
 	    }
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 
 	default:
 	  mac_ptr = skip_unknown_opcode (macinfo_type, opcode_definitions,
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 9f3297a..468e76d 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -6489,7 +6489,7 @@ process_die (struct die_info *die, struct dwarf2_cu *cu)
 	  && die->parent != NULL
 	  && die->parent->tag == DW_TAG_subprogram)
 	cu->processing_has_namespace_info = true;
-      /* Fall through.  */
+      [[fallthrough]];
     case DW_TAG_inlined_subroutine:
       read_func_scope (die, cu);
       break;
@@ -6531,7 +6531,7 @@ process_die (struct die_info *die, struct dwarf2_cu *cu)
 	 instead.  */
       if (cu->lang () != language_ada)
 	break;
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case DW_TAG_base_type:
     case DW_TAG_subrange_type:
     case DW_TAG_generic_subrange:
@@ -6559,7 +6559,7 @@ process_die (struct die_info *die, struct dwarf2_cu *cu)
 	break;
       /* The declaration is neither a global namespace nor a variable
 	 alias.  */
-      /* Fall through.  */
+      [[fallthrough]];
     case DW_TAG_imported_module:
       cu->processing_has_namespace_info = true;
       if (die->child != NULL && (die->tag == DW_TAG_imported_declaration
@@ -16433,7 +16433,7 @@ cooked_indexer::index_dies (cutu_reader *reader,
 	    case DW_TAG_module:
 	      if (this_entry == nullptr)
 		break;
-	      /* FALLTHROUGH */
+	      [[fallthrough]];
 	    case DW_TAG_namespace:
 	      /* We don't check THIS_ENTRY for a namespace, to handle
 		 the ancient G++ workaround pointed out above.  */
@@ -17140,7 +17140,7 @@ read_attribute_value (const struct die_reader_specs *reader,
 	  info_ptr += bytes_read;
 	  break;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case DW_FORM_line_strp:
       if (!cu->per_cu->is_dwz)
 	{
@@ -17150,7 +17150,7 @@ read_attribute_value (const struct die_reader_specs *reader,
 	  info_ptr += bytes_read;
 	  break;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case DW_FORM_GNU_strp_alt:
       {
 	dwz_file *dwz = dwarf2_get_dwz_file (per_objfile->per_bfd, true);
@@ -18963,7 +18963,7 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
 	  break;
 	case DW_TAG_template_value_param:
 	  suppress_add = 1;
-	  /* Fall through.  */
+	  [[fallthrough]];
 	case DW_TAG_constant:
 	case DW_TAG_variable:
 	case DW_TAG_member:
@@ -19140,7 +19140,7 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
 	  break;
 	case DW_TAG_template_type_param:
 	  suppress_add = 1;
-	  /* Fall through.  */
+	  [[fallthrough]];
 	case DW_TAG_class_type:
 	case DW_TAG_interface_type:
 	case DW_TAG_structure_type:
@@ -19194,7 +19194,7 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
 	case DW_TAG_unspecified_type:
 	  if (cu->lang () == language_ada)
 	    break;
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 	case DW_TAG_typedef:
 	case DW_TAG_array_type:
 	case DW_TAG_base_type:
@@ -19990,7 +19990,7 @@ determine_prefix (struct die_info *die, struct dwarf2_cu *cu)
 	      return parent_type->name ();
 	    return "";
 	  }
-	/* Fall through.  */
+	[[fallthrough]];
       default:
 	return determine_prefix (parent, cu);
       }
@@ -20174,7 +20174,7 @@ dwarf2_name (struct die_info *die, struct dwarf2_cu *cu)
     case DW_TAG_template_value_param:
       if (attr_name == nullptr)
 	return unnamed_template_tag_name (die, cu);
-      /* FALLTHROUGH.  */
+      [[fallthrough]];
     case DW_TAG_class_type:
     case DW_TAG_interface_type:
     case DW_TAG_structure_type:
diff --git a/gdb/eval.c b/gdb/eval.c
index 3358b0d..8192aeb 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -172,7 +172,7 @@ fetch_subexp_value (struct expression *exp,
 	case MEMORY_ERROR:
 	  if (!preserve_errors)
 	    break;
-	  /* Fall through.  */
+	  [[fallthrough]];
 	default:
 	  throw;
 	  break;
diff --git a/gdb/f-exp.y b/gdb/f-exp.y
index 18566af..e4e2171 100644
--- a/gdb/f-exp.y
+++ b/gdb/f-exp.y
@@ -1503,7 +1503,7 @@ yylex (void)
       /* Might be a floating point number.  */
       if (pstate->lexptr[1] < '0' || pstate->lexptr[1] > '9')
 	goto symbol;		/* Nope, must be a symbol.  */
-      /* FALL THRU.  */
+      [[fallthrough]];
       
     case '0':
     case '1':
@@ -1571,7 +1571,7 @@ yylex (void)
 
     case '%':
       last_was_structop = true;
-      /* Fall through.  */
+      [[fallthrough]];
     case '+':
     case '-':
     case '*':
diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index 211b83f..b56e194 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -1641,7 +1641,7 @@ fbsd_nat_target::stop_process (inferior *inf)
       if (status.sig () == GDB_SIGNAL_STOP)
 	break;
 
-      /* FALLTHROUGH */
+      [[fallthrough]];
     default:
       /* Some other event has occurred.  Save the current
 	 event.  */
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index aa2fce0..4c70c9b 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1101,7 +1101,7 @@ get_discrete_low_bound (struct type *type)
       if (!type->is_unsigned ())
 	return -(1 << (type->length () * TARGET_CHAR_BIT - 1));
 
-      /* fall through */
+      [[fallthrough]];
     case TYPE_CODE_CHAR:
       return 0;
 
@@ -1171,7 +1171,7 @@ get_discrete_high_bound (struct type *type)
 	  return -low - 1;
 	}
 
-      /* fall through */
+      [[fallthrough]];
     case TYPE_CODE_CHAR:
       {
 	/* This round-about calculation is to avoid shifting by
@@ -4436,7 +4436,7 @@ rank_one_type_parm_ptr (struct type *parm, struct type *arg, struct value *value
 		return NS_INTEGER_POINTER_CONVERSION_BADNESS;
 	    }
 	}
-      /* fall through  */
+      [[fallthrough]];
     case TYPE_CODE_ENUM:
     case TYPE_CODE_FLAGS:
     case TYPE_CODE_CHAR:
@@ -4608,7 +4608,7 @@ rank_one_type_parm_char (struct type *parm, struct type *arg, struct value *valu
 	return INTEGER_CONVERSION_BADNESS;
       else if (arg->length () < parm->length ())
 	return INTEGER_PROMOTION_BADNESS;
-      /* fall through */
+      [[fallthrough]];
     case TYPE_CODE_CHAR:
       /* Deal with signed, unsigned, and plain chars for C++ and
 	 with int cases falling through from previous case.  */
@@ -4741,7 +4741,7 @@ rank_one_type_parm_struct (struct type *parm, struct type *arg, struct value *va
       rank.subrank = distance_to_ancestor (parm, arg, 0);
       if (rank.subrank >= 0)
 	return sum_ranks (BASE_CONVERSION_BADNESS, rank);
-      /* fall through */
+      [[fallthrough]];
     default:
       return INCOMPATIBLE_TYPE_BADNESS;
     }
diff --git a/gdb/go-exp.y b/gdb/go-exp.y
index 28bf3f0..c9b9c0b 100644
--- a/gdb/go-exp.y
+++ b/gdb/go-exp.y
@@ -1054,7 +1054,7 @@ lex_one_token (struct parser_state *par_state)
 	    last_was_structop = 1;
 	  goto symbol;		/* Nope, must be a symbol. */
 	}
-      /* FALL THRU.  */
+      [[fallthrough]];
 
     case '0':
     case '1':
@@ -1129,7 +1129,7 @@ lex_one_token (struct parser_state *par_state)
 	    return ENTRY;
 	  }
       }
-      /* FALLTHRU */
+      [[fallthrough]];
     case '+':
     case '-':
     case '*':
diff --git a/gdb/go-valprint.c b/gdb/go-valprint.c
index 05788af..ca1e6b5 100644
--- a/gdb/go-valprint.c
+++ b/gdb/go-valprint.c
@@ -114,7 +114,7 @@ go_language::value_print_inner (struct value *val, struct ui_file *stream,
 	      break;
 	    }
 	}
-	/* Fall through.  */
+	[[fallthrough]];
 
       default:
 	c_value_print_inner (val, stream, recurse, options);
diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index 8efd858..e00c3bd 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -6011,7 +6011,7 @@ Do you want to stop the program?"),
 	  ir.addr -= 1;
 	  goto no_support;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case 0x0fb2:    /* lss Gv */
     case 0x0fb4:    /* lfs Gv */
     case 0x0fb5:    /* lgs Gv */
@@ -6248,7 +6248,7 @@ Do you want to stop the program?"),
 						  I386_SAVE_FPU_REGS))
 			    return -1;
 			}
-		      /* Fall through */
+		      [[fallthrough]];
 		    default:
 		      if (record_full_arch_list_add_mem (addr64, 2))
 			return -1;
@@ -6787,7 +6787,7 @@ Do you want to stop the program?"),
 	  ir.addr -= 1;
 	  goto no_support;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case 0xf5:    /* cmc */
     case 0xf8:    /* clc */
     case 0xf9:    /* stc */
@@ -7229,7 +7229,7 @@ Do you want to stop the program?"),
 	      else if (ir.rm == 1)
 		break;
 	    }
-	  /* Fall through.  */
+	  [[fallthrough]];
 	case 3:  /* lidt */
 	  if (ir.mod == 3)
 	    {
diff --git a/gdb/m2-typeprint.c b/gdb/m2-typeprint.c
index 72f9782..179c3fc 100644
--- a/gdb/m2-typeprint.c
+++ b/gdb/m2-typeprint.c
@@ -389,7 +389,7 @@ m2_get_discrete_bounds (struct type *type, LONGEST *lowp, LONGEST *highp)
 	      return 0;
 	    }
 	}
-      /* fall through */
+      [[fallthrough]];
     default:
       return get_discrete_bounds (type, lowp, highp);
     }
diff --git a/gdb/m2-valprint.c b/gdb/m2-valprint.c
index 96a566f..c4570da 100644
--- a/gdb/m2-valprint.c
+++ b/gdb/m2-valprint.c
@@ -373,7 +373,7 @@ m2_language::value_print_inner (struct value *val, struct ui_file *stream,
 	  gdb_printf (stream, "{...}");
 	  break;
 	}
-      /* Fall through.  */
+      [[fallthrough]];
     case TYPE_CODE_STRUCT:
       if (m2_is_long_set (type))
 	m2_print_long_set (type, valaddr, 0, address, stream);
@@ -451,7 +451,7 @@ m2_language::value_print_inner (struct value *val, struct ui_file *stream,
 	  value_print_inner (v, stream, recurse, options);
 	  break;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
 
     case TYPE_CODE_REF:
     case TYPE_CODE_ENUM:
diff --git a/gdb/machoread.c b/gdb/machoread.c
index 38c252c..87d30ec 100644
--- a/gdb/machoread.c
+++ b/gdb/machoread.c
@@ -292,7 +292,7 @@ macho_symtab_read (minimal_symbol_reader &reader,
 		    case N_FUN:
 		      if (sym->name == NULL || sym->name[0] == 0)
 			break;
-		      /* Fall through.  */
+		      [[fallthrough]];
 		    case N_STSYM:
 		      /* Interesting symbol.  */
 		      nbr_syms++;
diff --git a/gdb/mdebugread.c b/gdb/mdebugread.c
index fc73160..a280050 100644
--- a/gdb/mdebugread.c
+++ b/gdb/mdebugread.c
@@ -2582,7 +2582,7 @@ parse_partial_symbols (minimal_symbol_reader &reader,
 	     those too.  */
 	  if (name[0] == '.')
 	    continue;
-	  /* Fall through.  */
+	  [[fallthrough]];
 	default:
 	  ms_type = mst_unknown;
 	  unknown_ext_complaint (name);
@@ -3430,7 +3430,7 @@ parse_partial_symbols (minimal_symbol_reader &reader,
 					   mst_file_text,
 					   SECT_OFF_TEXT (objfile));
 
-		  /* FALLTHROUGH */
+		  [[fallthrough]];
 
 		case stProc:
 		  /* Ignore all parameter symbol records.  */
@@ -3666,7 +3666,7 @@ parse_partial_symbols (minimal_symbol_reader &reader,
 		default:
 		  unknown_ext_complaint (debug_info->ssext + psh->iss);
 		  /* Pretend it's global.  */
-		  /* Fall through.  */
+		  [[fallthrough]];
 		case stGlobal:
 		  /* Global common symbols are resolved by the runtime loader,
 		     ignore them.  */
diff --git a/gdb/mi/mi-cmd-stack.c b/gdb/mi/mi-cmd-stack.c
index 6982338..401e7c4 100644
--- a/gdb/mi/mi-cmd-stack.c
+++ b/gdb/mi/mi-cmd-stack.c
@@ -652,7 +652,7 @@ list_args_or_locals (const frame_print_options &fp_opts,
 		case PRINT_SIMPLE_VALUES:
 		  if (!mi_simple_type_p (sym2->type ()))
 		    break;
-		  /* FALLTHROUGH */
+		  [[fallthrough]];
 
 		case PRINT_ALL_VALUES:
 		  if (sym->is_argument ())
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index 72e500b..71e22ce 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -140,7 +140,7 @@ msymbol_is_function (struct objfile *objfile, minimal_symbol *minsym,
       /* Ignore function symbol that is not a function entry.  */
       if (msymbol_is_cold_clone (minsym))
 	return false;
-      /* fallthru */
+      [[fallthrough]];
     default:
       if (func_address_p != NULL)
 	*func_address_p = msym_addr;
diff --git a/gdb/mips-tdep.c b/gdb/mips-tdep.c
index 066c7c8..c7157c19 100644
--- a/gdb/mips-tdep.c
+++ b/gdb/mips-tdep.c
@@ -3992,7 +3992,7 @@ mips_deal_with_atomic_sequence (struct gdbarch *gdbarch, CORE_ADDR pc)
 		       && (itype_rt (insn) & 0x2) == 0);
 	  if (is_branch) /* BC1ANY2F, BC1ANY2T, BC1ANY4F, BC1ANY4T */
 	    break;
-	/* Fall through.  */
+	  [[fallthrough]];
 	case 18: /* COP2 */
 	case 19: /* COP3 */
 	  is_branch = (itype_rs (insn) == 8); /* BCzF, BCzFL, BCzT, BCzTL */
@@ -4100,7 +4100,7 @@ micromips_deal_with_atomic_sequence (struct gdbarch *gdbarch,
 		      || (insn & 0x3) != 0x1))
 				/* BC1ANY*: bits 010000 111xx xxx01 */
 		break;
-	      /* Fall through.  */
+	      [[fallthrough]];
 
 	    case 0x25: /* BEQ: bits 100101 */
 	    case 0x2d: /* BNE: bits 101101 */
@@ -4122,7 +4122,7 @@ micromips_deal_with_atomic_sequence (struct gdbarch *gdbarch,
 				/* JALR, JALR.HB: 000000 000x111100 111100 */
 				/* JALRS, JALRS.HB: 000000 010x111100 111100 */
 		break;
-	      /* Fall through.  */
+	      [[fallthrough]];
 
 	    case 0x1d: /* JALS: bits 011101 */
 	    case 0x35: /* J: bits 110101 */
diff --git a/gdb/msp430-tdep.c b/gdb/msp430-tdep.c
index 97d9073..f65948f 100644
--- a/gdb/msp430-tdep.c
+++ b/gdb/msp430-tdep.c
@@ -886,7 +886,7 @@ msp430_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 	      break;
 	    }
 	}
-	/* Fall through.  */
+	[[fallthrough]];
       default:
 	error (_("Unknown msp430 isa"));
 	break;
diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
index c0cebbb..89bf28b 100644
--- a/gdb/nat/linux-btrace.c
+++ b/gdb/nat/linux-btrace.c
@@ -895,8 +895,7 @@ linux_read_pt (btrace_data_pt *btrace, linux_btrace_target_info *tinfo,
     case BTRACE_READ_NEW:
       if (!perf_event_new_data (&tinfo->pev))
 	return BTRACE_ERR_NONE;
-
-      /* Fall through.  */
+      [[fallthrough]];
     case BTRACE_READ_ALL:
       perf_event_read_all (&tinfo->pev, &btrace->data, &btrace->size);
       return BTRACE_ERR_NONE;
diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index 7951bc3..ea95f95 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -454,7 +454,7 @@ windows_process_info::handle_exception (struct target_waitstatus *ourstatus,
 	  break;
 	}
 #endif
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case STATUS_WX86_BREAKPOINT:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT");
       ourstatus->set_stopped (GDB_SIGNAL_TRAP);
@@ -493,7 +493,7 @@ windows_process_info::handle_exception (struct target_waitstatus *ourstatus,
 	  break;
 	}
 	/* treat improperly formed exception as unknown */
-	/* FALLTHROUGH */
+	[[fallthrough]];
     default:
       /* Treat unhandled first chance exceptions specially.  */
       if (current_event.u.Exception.dwFirstChance)
diff --git a/gdb/nat/x86-dregs.c b/gdb/nat/x86-dregs.c
index 731093d..16669f6 100644
--- a/gdb/nat/x86-dregs.c
+++ b/gdb/nat/x86-dregs.c
@@ -289,7 +289,7 @@ Invalid hardware breakpoint type %d in x86_length_and_rw_bits.\n"),
       case 8:
 	if (TARGET_HAS_DR_LEN_8)
 	  return (DR_LEN_8 | rw);
-	/* FALL THROUGH */
+	[[fallthrough]];
       default:
 	internal_error (_("\
 Invalid hardware breakpoint length %d in x86_length_and_rw_bits.\n"), len);
diff --git a/gdb/p-exp.y b/gdb/p-exp.y
index 2360a50..b0f3348 100644
--- a/gdb/p-exp.y
+++ b/gdb/p-exp.y
@@ -1159,7 +1159,7 @@ yylex (void)
 	  goto symbol;		/* Nope, must be a symbol.  */
 	}
 
-      /* FALL THRU.  */
+      [[fallthrough]];
 
     case '0':
     case '1':
diff --git a/gdb/p-valprint.c b/gdb/p-valprint.c
index 0560162..1b7dab4 100644
--- a/gdb/p-valprint.c
+++ b/gdb/p-valprint.c
@@ -298,7 +298,7 @@ pascal_language::value_print_inner (struct value *val,
 	  gdb_printf (stream, "{...}");
 	  break;
 	}
-      /* Fall through.  */
+      [[fallthrough]];
     case TYPE_CODE_STRUCT:
       if (options->vtblprint && pascal_object_is_vtbl_ptr_type (type))
 	{
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 98f38b2..27a4eb3 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -482,7 +482,7 @@ print_scalar_formatted (const gdb_byte *valaddr, struct type *type,
 			       byte_order);
 	  break;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case 'f':
       print_floating (valaddr, type, stream);
       break;
diff --git a/gdb/record-btrace.c b/gdb/record-btrace.c
index 27b3753..a6c6888 100644
--- a/gdb/record-btrace.c
+++ b/gdb/record-btrace.c
@@ -231,7 +231,7 @@ record_btrace_get_cpu (void)
 
     case CS_NONE:
       record_btrace_cpu.vendor = CV_UNKNOWN;
-      /* Fall through.  */
+      [[fallthrough]];
     case CS_CPU:
       return &record_btrace_cpu;
     }
diff --git a/gdb/remote.c b/gdb/remote.c
index 22215b5..8ccc126 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -8123,7 +8123,7 @@ Packet: '%s'\n"),
       if (event->ws.kind () != TARGET_WAITKIND_IGNORE)
 	break;
 
-      /* fall through */
+      [[fallthrough]];
     case 'S':		/* Old style status, just signal only.  */
       {
 	int sig;
@@ -8647,7 +8647,7 @@ remote_target::wait_as (ptid_t ptid, target_waitstatus *status,
 	      putpkt (buf);
 	      break;
 	    }
-	  /* fallthrough */
+	  [[fallthrough]];
 	default:
 	  warning (_("Invalid remote reply: %s"), buf);
 	  break;
@@ -10002,7 +10002,7 @@ remote_target::putpkt_binary (const char *buf, int cnt)
 	      return 1;
 	    case '-':
 	      remote_debug_printf_nofunc ("Received Nak");
-	      /* FALLTHROUGH */
+	      [[fallthrough]];
 	    case SERIAL_TIMEOUT:
 	      tcount++;
 	      if (tcount > 3)
diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index 3725be4..8849483 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -3183,7 +3183,7 @@ riscv_arg_location (struct gdbarch *gdbarch,
 	  riscv_call_arg_struct (ainfo, cinfo);
 	  break;
 	}
-      /* FALLTHROUGH */
+      [[fallthrough]];
 
     default:
       riscv_call_arg_scalar_int (ainfo, cinfo);
diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index fef47f8..16f3da9 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -4309,7 +4309,7 @@ ppc_process_record_op4 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 39:		/* Vector Multiply-Sum Unsigned Halfword Saturate */
     case 41:		/* Vector Multiply-Sum Signed Halfword Saturate */
       record_full_arch_list_add_reg (regcache, PPC_VSCR_REGNUM);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 20:		/* Move To VSR Byte Mask Immediate opcode, b2 = 0,
 			   ignore bit 31 */
     case 21:		/* Move To VSR Byte Mask Immediate opcode, b2 = 1,
@@ -4375,7 +4375,7 @@ ppc_process_record_op4 (struct gdbarch *gdbarch, struct regcache *regcache,
 	  && vra != 7	/* Decimal Convert From National */
 	  && vra != 31)	/* Decimal Set Sign */
 	break;
-      /* Fall through.  */
+      [[fallthrough]];
 			/* 5.16 Decimal Integer Arithmetic Instructions */
     case 1:		/* Decimal Add Modulo */
     case 65:		/* Decimal Subtract Modulo */
@@ -4564,7 +4564,7 @@ ppc_process_record_op4 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 970:		/* Vector Convert To Signed Fixed-Point Word Saturate */
     case 906:		/* Vector Convert To Unsigned Fixed-Point Word Saturate */
       record_full_arch_list_add_reg (regcache, PPC_VSCR_REGNUM);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 12:		/* Vector Merge High Byte */
     case 14:		/* Vector Pack Unsigned Halfword Unsigned Modulo */
     case 76:		/* Vector Merge High Halfword */
@@ -4897,7 +4897,7 @@ ppc_process_record_op19 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 560:		/* Branch Conditional to Branch Target Address Register */
       if ((PPC_BO (insn) & 0x4) == 0)
 	record_full_arch_list_add_reg (regcache, tdep->ppc_ctr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 528:		/* Branch Conditional to Count Register */
       if (PPC_LK (insn))
 	record_full_arch_list_add_reg (regcache, tdep->ppc_lr_regnum);
@@ -4988,7 +4988,7 @@ ppc_process_record_op31 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 491:		/* Divide Word */
       if (PPC_OE (insn))
 	record_full_arch_list_add_reg (regcache, tdep->ppc_xer_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 9:		/* Multiply High Doubleword Unsigned */
     case 11:		/* Multiply High Word Unsigned */
     case 73:		/* Multiply High Doubleword */
@@ -5080,7 +5080,7 @@ ppc_process_record_op31 (struct gdbarch *gdbarch, struct regcache *regcache,
       record_full_arch_list_add_reg (regcache, tdep->ppc_xer_regnum);
       record_full_arch_list_add_reg (regcache,
 				     tdep->ppc_gp0_regnum + PPC_RA (insn));
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 0:		/* Compare */
     case 32:		/* Compare logical */
     case 144:		/* Move To Condition Register Fields */
@@ -5103,7 +5103,7 @@ ppc_process_record_op31 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 373:		/* Load Word Algebraic with Update Indexed */
       record_full_arch_list_add_reg (regcache,
 				     tdep->ppc_gp0_regnum + PPC_RA (insn));
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 21:		/* Load Doubleword Indexed */
     case 52:		/* Load Byte And Reserve Indexed */
     case 116:		/* Load Halfword And Reserve Indexed */
@@ -5176,7 +5176,7 @@ ppc_process_record_op31 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 631:		/* Load Floating-Point Double with Update Indexed */
       record_full_arch_list_add_reg (regcache,
 				     tdep->ppc_gp0_regnum + PPC_RA (insn));
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 535:		/* Load Floating-Point Single Indexed */
     case 599:		/* Load Floating-Point Double Indexed */
     case 855:		/* Load Floating-Point as Integer Word Algebraic Indexed */
@@ -5272,7 +5272,7 @@ ppc_process_record_op31 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 759:		/* Store Floating-Point Double with Update Indexed */
       record_full_arch_list_add_reg (regcache,
 				     tdep->ppc_gp0_regnum + PPC_RA (insn));
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 135:		/* Store Vector Element Byte Indexed */
     case 167:		/* Store Vector Element Halfword Indexed */
     case 199:		/* Store Vector Element Word Indexed */
@@ -5566,7 +5566,7 @@ ppc_process_record_op31 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 878:		/* Transaction Abort Doubleword Conditional Immediate */
     case 910:		/* Transaction Abort */
       record_full_arch_list_add_reg (regcache, tdep->ppc_ps_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 718:		/* Transaction Check */
       record_full_arch_list_add_reg (regcache, tdep->ppc_cr_regnum);
       return 0;
@@ -5790,7 +5790,7 @@ ppc_process_record_op60_XX2 (struct gdbarch *gdbarch,
     case 24:	/* VSX Vector Convert Half-Precision format to
 		   Single-Precision format */
       record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-      /* Fall-through */
+      [[fallthrough]];
     case 0:	/* VSX Vector Extract Exponent Double-Precision */
     case 1:	/* VSX Vector Extract Significand Double-Precision */
     case 7:	/* VSX Vector Byte-Reverse Halfword */
@@ -5884,7 +5884,7 @@ ppc_process_record_op60 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 19:		/* VSX Scalar Compare Greater Than or Equal
 			   Double-Precision */
       record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 240:		/* VSX Vector Copy Sign Double-Precision */
     case 208:		/* VSX Vector Copy Sign Single-Precision */
     case 130:		/* VSX Logical AND */
@@ -6071,7 +6071,7 @@ ppc_process_record_op60 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 203:		/* VSX Vector Square Root Double-Precision */
     case 139:		/* VSX Vector Square Root Single-Precision */
       record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 345:		/* VSX Scalar Absolute Value Double-Precision */
     case 267:		/* VSX Scalar Convert Scalar Single-Precision to
 			   Vector Single-Precision format Non-signalling */
@@ -6094,7 +6094,7 @@ ppc_process_record_op60 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 298:		/* VSX Scalar Test Data Class Single-Precision */
     case 362:		/* VSX Scalar Test Data Class Double-Precision */
       record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 106:		/* VSX Scalar Test for software Square Root
 			   Double-Precision */
     case 234:		/* VSX Vector Test for software Square Root
@@ -6366,7 +6366,7 @@ ppc_process_record_op63 (struct gdbarch *gdbarch, struct regcache *regcache,
 	  case 22:	/* Move From FPSCR Control & set RN */
 	  case 23:	/* Move From FPSCR Control & set RN Immediate */
 	    record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-	    /* Fall through.  */
+	    [[fallthrough]];
 	  case 0:	/* Move From FPSCR */
 	  case 24:	/* Move From FPSCR Lightweight */
 	    if (PPC_FIELD (insn, 11, 5) == 0 && PPC_RC (insn))
@@ -6412,7 +6412,7 @@ ppc_process_record_op63 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 644:		/* VSX Scalar Compare Unordered Quad-Precision */
     case 708:		/* VSX Scalar Test Data Class Quad-Precision */
       record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 128:		/* Floating Test for software Divide */
     case 160:		/* Floating Test for software Square Root */
       record_full_arch_list_add_reg (regcache, tdep->ppc_cr_regnum);
@@ -6449,7 +6449,7 @@ ppc_process_record_op63 (struct gdbarch *gdbarch, struct regcache *regcache,
       }
 
       record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 68:		/* VSX Scalar Compare Equal Quad-Precision */
     case 196:		/* VSX Scalar Compare Greater Than or Equal
 			   Quad-Precision */
@@ -6457,7 +6457,7 @@ ppc_process_record_op63 (struct gdbarch *gdbarch, struct regcache *regcache,
     case 676:		/* VSX Scalar Maximum Type-C Quad-Precision */
     case 740:		/* VSX Scalar Minimum Type-C Quad-Precision */
       record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 100:		/* VSX Scalar Copy Sign Quad-Precision */
     case 868:		/* VSX Scalar Insert Exponent Quad-Precision */
       ppc_record_vsr (regcache, tdep, PPC_VRT (insn) + 32);
@@ -6468,7 +6468,7 @@ ppc_process_record_op63 (struct gdbarch *gdbarch, struct regcache *regcache,
 	{
 	case 27:	/* VSX Scalar Square Root Quad-Precision */
 	  record_full_arch_list_add_reg (regcache, tdep->ppc_fpscr_regnum);
-	  /* FALL-THROUGH */
+	  [[fallthrough]];
 	case 0:		/* VSX Scalar Absolute Quad-Precision */
 	case 2:		/* VSX Scalar Extract Exponent Quad-Precision */
 	case 8:		/* VSX Scalar Negative Absolute Quad-Precision */
@@ -7233,10 +7233,10 @@ ppc_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
 
     case 13:		/* Add Immediate Carrying and Record */
       record_full_arch_list_add_reg (regcache, tdep->ppc_cr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 12:		/* Add Immediate Carrying */
       record_full_arch_list_add_reg (regcache, tdep->ppc_xer_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 14:		/* Add Immediate */
     case 15:		/* Add Immediate Shifted */
       record_full_arch_list_add_reg (regcache,
@@ -7246,7 +7246,7 @@ ppc_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
     case 16:		/* Branch Conditional */
       if ((PPC_BO (insn) & 0x4) == 0)
 	record_full_arch_list_add_reg (regcache, tdep->ppc_ctr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 18:		/* Branch */
       if (PPC_LK (insn))
 	record_full_arch_list_add_reg (regcache, tdep->ppc_lr_regnum);
@@ -7275,7 +7275,7 @@ ppc_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
     case 28:		/* AND Immediate */
     case 29:		/* AND Immediate Shifted */
       record_full_arch_list_add_reg (regcache, tdep->ppc_cr_regnum);
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 24:		/* OR Immediate */
     case 25:		/* OR Immediate Shifted */
     case 26:		/* XOR Immediate */
@@ -7295,7 +7295,7 @@ ppc_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
     case 43:		/* Load Halfword Algebraic with Update */
       record_full_arch_list_add_reg (regcache,
 				     tdep->ppc_gp0_regnum + PPC_RA (insn));
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 32:		/* Load Word and Zero */
     case 34:		/* Load Byte and Zero */
     case 40:		/* Load Halfword and Zero */
@@ -7319,7 +7319,7 @@ ppc_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
     case 51:		/* Load Floating-Point Double with Update */
       record_full_arch_list_add_reg (regcache,
 				     tdep->ppc_gp0_regnum + PPC_RA (insn));
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 48:		/* Load Floating-Point Single */
     case 50:		/* Load Floating-Point Double */
       record_full_arch_list_add_reg (regcache,
@@ -7347,7 +7347,7 @@ ppc_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
     case 55:		/* Store Floating-Point Double with Update */
       record_full_arch_list_add_reg (regcache,
 				     tdep->ppc_gp0_regnum + PPC_RA (insn));
-      /* FALL-THROUGH */
+      [[fallthrough]];
     case 36:		/* Store Word */
     case 38:		/* Store Byte */
     case 44:		/* Store Halfword */
diff --git a/gdb/rust-parse.c b/gdb/rust-parse.c
index d2f6008..aaf4cef 100644
--- a/gdb/rust-parse.c
+++ b/gdb/rust-parse.c
@@ -1386,7 +1386,7 @@ rust_parser::parse_binop (bool required)
 
 	case COMPOUND_ASSIGN:
 	  compound_assign_op = current_opcode;
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 	case '=':
 	  precedence = ASSIGN_PREC;
 	  lex ();
@@ -1831,7 +1831,7 @@ rust_parser::parse_path (bool for_expr)
       if (current_token != COLONCOLON)
 	return "self";
       lex ();
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case KW_SUPER:
       while (current_token == KW_SUPER)
 	{
diff --git a/gdb/s390-tdep.c b/gdb/s390-tdep.c
index 54b5c89..5b58cb3 100644
--- a/gdb/s390-tdep.c
+++ b/gdb/s390-tdep.c
@@ -4376,7 +4376,7 @@ ex:
 		    break;
 		  }
 		/* For other instructions... */
-		/* Fall through.  */
+		[[fallthrough]];
 	      default:
 		gdb_printf (gdb_stdlog, "Warning: Unknown KM* function %02x at %s.\n",
 			    (int)tmp, paddress (gdbarch, addr));
@@ -4685,7 +4685,7 @@ ex:
 		    break;
 		  }
 		/* For KLMD...  */
-		/* Fall through.  */
+		[[fallthrough]];
 	      default:
 		gdb_printf (gdb_stdlog, "Warning: Unknown KMAC function %02x at %s.\n",
 			    (int)tmp, paddress (gdbarch, addr));
@@ -6542,7 +6542,7 @@ ex:
 	      /* op3c */
 	      if (record_full_arch_list_add_reg (regcache, S390_R0_REGNUM + inib[3]))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x0c: /* CSST */
 	      /* op4 */
 	      if (record_full_arch_list_add_mem (oaddr2, 4))
@@ -6557,7 +6557,7 @@ ex:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 4))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x10: /* CSDST */
 	      /* op6 */
 	      if (target_read_memory (oaddr2 + 0x68, buf, 8))
@@ -6573,7 +6573,7 @@ ex:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 4))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x04: /* CS */
 CS:
 	      /* op1c */
@@ -6598,7 +6598,7 @@ CS:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 8))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x11: /* CSDSTG */
 	      /* op6 */
 	      if (target_read_memory (oaddr2 + 0x68, buf, 8))
@@ -6607,7 +6607,7 @@ CS:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 8))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x0d: /* CSSTG */
 CSSTG:
 	      /* op4 */
@@ -6617,7 +6617,7 @@ CSSTG:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 8))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x05: /* CSG */
 	      /* op1c */
 	      if (record_full_arch_list_add_mem (oaddr2 + 0x08, 8))
@@ -6631,7 +6631,7 @@ CSSTG:
 	      /* op3c */
 	      if (s390_record_gpr_g (gdbarch, regcache, inib[3]))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x0e: /* CSSTGR */
 	      /* op4 */
 	      if (record_full_arch_list_add_mem (oaddr2, 8))
@@ -6646,7 +6646,7 @@ CSSTG:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 8))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x12: /* CSDSTGR */
 	      /* op6 */
 	      if (target_read_memory (oaddr2 + 0x68, buf, 8))
@@ -6662,7 +6662,7 @@ CSSTG:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 8))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x06: /* CSGR */
 CSGR:
 	      /* op1c */
@@ -6687,7 +6687,7 @@ CSGR:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 16))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x13: /* CSDSTX */
 	      /* op6 */
 	      if (target_read_memory (oaddr2 + 0x68, buf, 8))
@@ -6696,7 +6696,7 @@ CSGR:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 16))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x0f: /* CSSTX */
 CSSTX:
 	      /* op4 */
@@ -6706,7 +6706,7 @@ CSSTX:
 	      oaddr3 = s390_record_address_mask (gdbarch, regcache, oaddr3);
 	      if (record_full_arch_list_add_mem (oaddr3, 16))
 		return -1;
-	      /* fallthru */
+	      [[fallthrough]];
 	    case 0x07: /* CSX */
 	      /* op1c */
 	      if (record_full_arch_list_add_mem (oaddr2 + 0x00, 16))
diff --git a/gdb/stabsread.c b/gdb/stabsread.c
index c81ae42..754f824 100644
--- a/gdb/stabsread.c
+++ b/gdb/stabsread.c
@@ -1095,7 +1095,7 @@ define_symbol (CORE_ADDR valu, const char *string, int desc, int type,
 	    }
 	  break;
 	}
-      /* Fall through.  */
+      [[fallthrough]];
 
     case 'P':
       /* acc seems to use P to declare the prototypes of functions that
@@ -1106,7 +1106,7 @@ define_symbol (CORE_ADDR valu, const char *string, int desc, int type,
 	  sym->set_type (read_type (&p, objfile));
 	  goto process_prototype_types;
 	}
-      /*FALLTHROUGH */
+      [[fallthrough]];
 
     case 'R':
       /* Parameter which is in a register.  */
@@ -2494,7 +2494,7 @@ read_member_functions (struct stab_field_info *fip, const char **pp,
 	      complaint (_("member function type missing, got '%c'"),
 			 (*pp)[-1]);
 	      /* Normal member function.  */
-	      /* Fall through.  */
+	      [[fallthrough]];
 
 	    case '.':
 	      /* normal member function.  */
diff --git a/gdb/symfile.c b/gdb/symfile.c
index c5af186..09aa70b 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -3043,7 +3043,7 @@ section_is_mapped (struct obj_section *osect)
 	  if (osect->ovly_mapped == -1)
 	    gdbarch_overlay_update (gdbarch, osect);
 	}
-      /* fall thru */
+      [[fallthrough]];
     case ovly_on:		/* overlay debugging manual */
       return osect->ovly_mapped == 1;
     }
diff --git a/gdb/utils.c b/gdb/utils.c
index 7a1841b..5ec8c56 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -218,7 +218,7 @@ can_dump_core (enum resource_limit_kind limit_kind)
     case LIMIT_CUR:
       if (rlim.rlim_cur == 0)
 	return 0;
-      /* Fall through.  */
+      [[fallthrough]];
 
     case LIMIT_MAX:
       if (rlim.rlim_max == 0)
diff --git a/gdb/valops.c b/gdb/valops.c
index a8760cc..6521580a1 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -1280,7 +1280,7 @@ value_assign (struct value *toval, struct value *fromval)
 	    break;
 	  }
       }
-      /* Fall through.  */
+      [[fallthrough]];
 
     default:
       error (_("Left operand of assignment is not an lvalue."));
@@ -2820,7 +2820,7 @@ find_overload_match (gdb::array_view<value *> args,
 		   case where a xmethod is better than the source
 		   method, except when the xmethod match quality is
 		   non-standard.  */
-		/* FALLTHROUGH */
+		[[fallthrough]];
 	      case 1: /* Src method and ext method are incompatible.  */
 		/* If ext method match is not standard, then let source method
 		   win.  Otherwise, fallthrough to let xmethod win.  */
@@ -2832,7 +2832,7 @@ find_overload_match (gdb::array_view<value *> args,
 		    method_match_quality = src_method_match_quality;
 		    break;
 		  }
-		/* FALLTHROUGH */
+		[[fallthrough]];
 	      case 2: /* Ext method is champion.  */
 		method_oload_champ = ext_method_oload_champ;
 		method_badness = ext_method_badness;
diff --git a/gdb/value.c b/gdb/value.c
index 7067ae94..b4da967 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -3336,7 +3336,7 @@ pack_long (gdb_byte *buf, struct type *type, LONGEST num)
     {
     case TYPE_CODE_RANGE:
       num -= type->bounds ()->bias;
-      /* Fall through.  */
+      [[fallthrough]];
     case TYPE_CODE_INT:
     case TYPE_CODE_CHAR:
     case TYPE_CODE_ENUM:
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 39a4e79..6544118 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -2291,14 +2291,14 @@ redir_open (const char *redir_string, int *inp, int *out, int *err)
     {
     case '0':
       fname++;
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case '<':
       fd = inp;
       mode = O_RDONLY;
       break;
     case '1': case '2':
       fname++;
-      /* FALLTHROUGH */
+      [[fallthrough]];
     case '>':
       fd = (rc == '2') ? err : out;
       mode = O_WRONLY | O_CREAT;
diff --git a/gdb/xcoffread.c b/gdb/xcoffread.c
index 829fc1f..856fa13 100644
--- a/gdb/xcoffread.c
+++ b/gdb/xcoffread.c
@@ -1532,7 +1532,7 @@ process_xcoff_symbol (struct xcoff_symbol *cs, struct objfile *objfile)
 	default:
 	  complaint (_("Unexpected storage class: %d"),
 		     cs->c_sclass);
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 
 	case C_DECL:
 	case C_PSYM:
@@ -2359,7 +2359,7 @@ scan_xcoff_symtab (minimal_symbol_reader &reader,
 	    complaint (_("Storage class %d not recognized during scan"),
 		       sclass);
 	  }
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 
 	case C_FCN:
 	  /* C_FCN is .bf and .ef symbols.  I think it is sufficient
diff --git a/gdb/z80-tdep.c b/gdb/z80-tdep.c
index ae32855..f0cc7c0 100644
--- a/gdb/z80-tdep.c
+++ b/gdb/z80-tdep.c
@@ -799,7 +799,7 @@ z80_software_single_step (struct regcache *regcache)
       break;
     case insn_jr_cc_d:
       opcode &= 030; /* JR NZ,d has cc equal to 040, but others 000 */
-      /* fall through */
+      [[fallthrough]];
     case insn_jp_cc_nn:
     case insn_call_cc_nn:
     case insn_ret_cc:
diff --git a/gdbserver/netbsd-low.cc b/gdbserver/netbsd-low.cc
index 4defd79..10d8d28 100644
--- a/gdbserver/netbsd-low.cc
+++ b/gdbserver/netbsd-low.cc
@@ -410,7 +410,7 @@ netbsd_process_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 	case TARGET_WAITKIND_THREAD_CREATED:
 	case TARGET_WAITKIND_THREAD_EXITED:
 	  /* The core needlessly stops on these events.  */
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 	case TARGET_WAITKIND_SPURIOUS:
 	  /* Spurious events are unhandled by the gdbserver core.  */
 	  if (ptrace (PT_CONTINUE, current_process ()->pid, (void *) 1, 0)
diff --git a/gdbsupport/btrace-common.cc b/gdbsupport/btrace-common.cc
index 932a118..c09fd50 100644
--- a/gdbsupport/btrace-common.cc
+++ b/gdbsupport/btrace-common.cc
@@ -134,8 +134,7 @@ btrace_data_append (struct btrace_data *dst,
 	case BTRACE_FORMAT_NONE:
 	  dst->format = BTRACE_FORMAT_BTS;
 	  dst->variant.bts.blocks = new std::vector<btrace_block>;
-
-	  /* Fall-through.  */
+	  [[fallthrough]];
 	case BTRACE_FORMAT_BTS:
 	  {
 	    unsigned int blk;
@@ -163,8 +162,7 @@ btrace_data_append (struct btrace_data *dst,
 	  dst->format = BTRACE_FORMAT_PT;
 	  dst->variant.pt.data = NULL;
 	  dst->variant.pt.size = 0;
-
-	  /* fall-through.  */
+	  [[fallthrough]];
 	case BTRACE_FORMAT_PT:
 	  {
 	    gdb_byte *data;
diff --git a/gdbsupport/format.cc b/gdbsupport/format.cc
index 6e5a3cb..85d1f9a 100644
--- a/gdbsupport/format.cc
+++ b/gdbsupport/format.cc
@@ -257,14 +257,14 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
 	  case 'u':
 	    if (seen_hash)
 	      bad = 1;
-	    /* FALLTHROUGH */
+	    [[fallthrough]];
 
 	  case 'o':
 	  case 'x':
 	  case 'X':
 	    if (seen_space || seen_plus)
 	      bad = 1;
-	  /* FALLTHROUGH */
+	  [[fallthrough]];
 
 	  case 'd':
 	  case 'i':