[1/7] 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
---
 gdb/aarch64-tdep.c                  |  2 +-
 gdb/ada-exp.y                       |  2 +-
 gdb/ada-lang.c                      |  2 +-
 gdb/ada-valprint.c                  |  2 +-
 gdb/amd64-windows-tdep.c            |  2 +-
 gdb/arch/arm.c                      |  2 +-
 gdb/arm-tdep.c                      |  2 +-
 gdb/c-exp.y                         |  6 ++--
 gdb/cli/cli-setshow.c               |  2 +-
 gdb/coffread.c                      |  4 +--
 gdb/compile/compile-c-support.c     |  2 +-
 gdb/compile/compile-c-symbols.c     |  2 +-
 gdb/compile/compile-cplus-symbols.c |  2 +-
 gdb/cp-name-parser.y                |  4 +--
 gdb/cp-support.c                    |  2 +-
 gdb/ctfread.c                       |  2 +-
 gdb/d-exp.y                         |  4 +--
 gdb/d-valprint.c                    |  2 +-
 gdb/dbxread.c                       |  2 +-
 gdb/disasm-selftests.c              |  2 +-
 gdb/dwarf2/macro.c                  |  4 +--
 gdb/dwarf2/read.c                   | 22 ++++++------
 gdb/eval.c                          |  2 +-
 gdb/f-exp.y                         |  4 +--
 gdb/fbsd-nat.c                      |  2 +-
 gdb/gdbtypes.c                      | 10 +++---
 gdb/go-exp.y                        |  4 +--
 gdb/go-valprint.c                   |  2 +-
 gdb/i386-tdep.c                     |  8 ++---
 gdb/m2-typeprint.c                  |  2 +-
 gdb/m2-valprint.c                   |  4 +--
 gdb/machoread.c                     |  2 +-
 gdb/mdebugread.c                    |  6 ++--
 gdb/mi/mi-cmd-stack.c               |  2 +-
 gdb/minsyms.c                       |  2 +-
 gdb/mips-tdep.c                     |  6 ++--
 gdb/msp430-tdep.c                   |  2 +-
 gdb/nat/linux-btrace.c              |  3 +-
 gdb/nat/windows-nat.c               |  4 +--
 gdb/nat/x86-dregs.c                 |  2 +-
 gdb/p-exp.y                         |  2 +-
 gdb/p-valprint.c                    |  2 +-
 gdb/printcmd.c                      |  2 +-
 gdb/record-btrace.c                 |  2 +-
 gdb/remote.c                        |  6 ++--
 gdb/riscv-tdep.c                    |  2 +-
 gdb/rs6000-tdep.c                   | 52 ++++++++++++++---------------
 gdb/rust-parse.c                    |  4 +--
 gdb/s390-tdep.c                     | 28 ++++++++--------
 gdb/stabsread.c                     |  6 ++--
 gdb/symfile.c                       |  2 +-
 gdb/utils.c                         |  2 +-
 gdb/valops.c                        |  6 ++--
 gdb/value.c                         |  2 +-
 gdb/windows-nat.c                   |  4 +--
 gdb/xcoffread.c                     |  4 +--
 gdb/z80-tdep.c                      |  2 +-
 gdbserver/netbsd-low.cc             |  2 +-
 gdbsupport/btrace-common.cc         |  6 ++--
 gdbsupport/format.cc                |  4 +--
 60 files changed, 140 insertions(+), 143 deletions(-)
  

On 10/16/23 4:02 PM, Tom Tromey wrote:
> 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

The fbsd-nat.c change is explicitly ok with me.

The series in general seems ok to me though I didn't thorougly
review all of this patch in particular.
  

On 10/17/23 00:02, Tom Tromey wrote:
> 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
> ---
>  gdb/aarch64-tdep.c                  |  2 +-
>  gdb/ada-exp.y                       |  2 +-
>  gdb/ada-lang.c                      |  2 +-
>  gdb/ada-valprint.c                  |  2 +-
>  gdb/amd64-windows-tdep.c            |  2 +-
>  gdb/arch/arm.c                      |  2 +-
>  gdb/arm-tdep.c                      |  2 +-
>  gdb/c-exp.y                         |  6 ++--
>  gdb/cli/cli-setshow.c               |  2 +-
>  gdb/coffread.c                      |  4 +--
>  gdb/compile/compile-c-support.c     |  2 +-
>  gdb/compile/compile-c-symbols.c     |  2 +-
>  gdb/compile/compile-cplus-symbols.c |  2 +-
>  gdb/cp-name-parser.y                |  4 +--
>  gdb/cp-support.c                    |  2 +-
>  gdb/ctfread.c                       |  2 +-
>  gdb/d-exp.y                         |  4 +--
>  gdb/d-valprint.c                    |  2 +-
>  gdb/dbxread.c                       |  2 +-
>  gdb/disasm-selftests.c              |  2 +-
>  gdb/dwarf2/macro.c                  |  4 +--
>  gdb/dwarf2/read.c                   | 22 ++++++------
>  gdb/eval.c                          |  2 +-
>  gdb/f-exp.y                         |  4 +--
>  gdb/fbsd-nat.c                      |  2 +-
>  gdb/gdbtypes.c                      | 10 +++---
>  gdb/go-exp.y                        |  4 +--
>  gdb/go-valprint.c                   |  2 +-
>  gdb/i386-tdep.c                     |  8 ++---
>  gdb/m2-typeprint.c                  |  2 +-
>  gdb/m2-valprint.c                   |  4 +--
>  gdb/machoread.c                     |  2 +-
>  gdb/mdebugread.c                    |  6 ++--
>  gdb/mi/mi-cmd-stack.c               |  2 +-
>  gdb/minsyms.c                       |  2 +-
>  gdb/mips-tdep.c                     |  6 ++--
>  gdb/msp430-tdep.c                   |  2 +-
>  gdb/nat/linux-btrace.c              |  3 +-
>  gdb/nat/windows-nat.c               |  4 +--
>  gdb/nat/x86-dregs.c                 |  2 +-
>  gdb/p-exp.y                         |  2 +-
>  gdb/p-valprint.c                    |  2 +-
>  gdb/printcmd.c                      |  2 +-
>  gdb/record-btrace.c                 |  2 +-
>  gdb/remote.c                        |  6 ++--
>  gdb/riscv-tdep.c                    |  2 +-
>  gdb/rs6000-tdep.c                   | 52 ++++++++++++++---------------
>  gdb/rust-parse.c                    |  4 +--
>  gdb/s390-tdep.c                     | 28 ++++++++--------
>  gdb/stabsread.c                     |  6 ++--
>  gdb/symfile.c                       |  2 +-
>  gdb/utils.c                         |  2 +-
>  gdb/valops.c                        |  6 ++--
>  gdb/value.c                         |  2 +-
>  gdb/windows-nat.c                   |  4 +--
>  gdb/xcoffread.c                     |  4 +--
>  gdb/z80-tdep.c                      |  2 +-
>  gdbserver/netbsd-low.cc             |  2 +-
>  gdbsupport/btrace-common.cc         |  6 ++--
>  gdbsupport/format.cc                |  4 +--
>  60 files changed, 140 insertions(+), 143 deletions(-)
> 
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index eaae2d91047..ba37b4969a3 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 3280a483a5e..fcb5aa4379b 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 ff7222c7eed..1a591567cda 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 f1c4e8b0b70..0930df81061 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 9d69ec282d2..6be43434121 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 4720c201c53..6fc4c0e11cd 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 58c550af183..66e258199d7 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 a27dbfa608f..2b4c21850d3 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 c7bbac1666d..11f93068b68 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 4a6a83b15ad..256d6335468 100644
> --- a/gdb/coffread.c
> +++ b/gdb/coffread.c
> @@ -914,7 +914,7 @@ 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:
> @@ -952,7 +952,7 @@ 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 20a7bb4e0d4..46318dba1b2 100644
> --- a/gdb/compile/compile-c-support.c
> +++ b/gdb/compile/compile-c-support.c
> @@ -268,7 +268,7 @@ 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 5982178170c..a80b9a43156 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 1edbf8f64b5..5cffe5cfebb 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 061882363be..4f407f504ef 100644
> --- a/gdb/cp-name-parser.y
> +++ b/gdb/cp-name-parser.y
> @@ -1605,7 +1605,7 @@ yylex (YYSTYPE *lvalp, cpname_state *state)
>  					  sizeof "(anonymous namespace)" - 1);
>  	  return NAME;
>  	}
> -	/* FALL THROUGH */
> +	[[fallthrough]];
>  
>      case ')':
>      case ',':
> @@ -1642,7 +1642,7 @@ 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 882acfb62a2..085d7c976e2 100644
> --- a/gdb/cp-support.c
> +++ b/gdb/cp-support.c
> @@ -532,7 +532,7 @@ 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 c74ec044c18..03a042ec38c 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 6c5569a1c8d..e2507982d50 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 38fb2a07c1f..4c3ea227750 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 b92193bdadd..99d9fba96ea 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 0cf766a48b7..200d33aff4e 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 2e88e670216..7d86d16d0e3 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 a2c1428b0f4..665912aa845 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -6667,7 +6667,7 @@ 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;
> @@ -6709,7 +6709,7 @@ 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:
> @@ -6737,7 +6737,7 @@ 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
> @@ -16627,7 +16627,7 @@ 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.  */
> @@ -17334,7 +17334,7 @@ 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)
>  	{
> @@ -17344,7 +17344,7 @@ 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);
> @@ -19157,7 +19157,7 @@ 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:
> @@ -19334,7 +19334,7 @@ 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:
> @@ -19389,7 +19389,7 @@ 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:
> @@ -20186,7 +20186,7 @@ determine_prefix (struct die_info *die, struct dwarf2_cu *cu)
>  	      return parent_type->name ();
>  	    return "";
>  	  }
> -	/* Fall through.  */
> +	[[fallthrough]];
>        default:
>  	return determine_prefix (parent, cu);
>        }
> @@ -20370,7 +20370,7 @@ 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 3358b0d8d32..8192aeba364 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 18566afd67f..e4e2171d641 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 211b83f555a..b56e194b7d5 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 284793c055d..e310648d410 100644
> --- a/gdb/gdbtypes.c
> +++ b/gdb/gdbtypes.c
> @@ -1102,7 +1102,7 @@ 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;
>  
> @@ -1172,7 +1172,7 @@ 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
> @@ -4437,7 +4437,7 @@ 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:
> @@ -4609,7 +4609,7 @@ 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.  */
> @@ -4742,7 +4742,7 @@ 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 28bf3f0ab33..c9b9c0b1ab7 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 05788af15a6..ca1e6b5ba6f 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 560f16aa0e3..12b98d6f20d 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 72f978205ab..179c3fccc30 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 96a566fb810..c4570da2e18 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 38c252c2861..87d30ec8587 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 fc731605991..a28005031e6 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 6982338751a..401e7c40726 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 72e500be959..71e22ce1a90 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 d40d28e85de..17bc9db6b89 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 97d9073efbb..f65948f01d8 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 aa02f193399..3215c4a7410 100644
> --- a/gdb/nat/linux-btrace.c
> +++ b/gdb/nat/linux-btrace.c
> @@ -896,8 +896,7 @@ 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 bf4c4387886..3066ff96a19 100644
> --- a/gdb/nat/windows-nat.c
> +++ b/gdb/nat/windows-nat.c
> @@ -456,7 +456,7 @@ 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);
> @@ -495,7 +495,7 @@ 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 731093dfa73..16669f69657 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 2360a500476..b0f334897ad 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 fb9386293a6..678df5eee0d 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 5afbc565cf7..f0be4268e60 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 7a7d7617bc9..5aa8c096c6e 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 b405cb6abf7..3e90964f027 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -7985,7 +7985,7 @@ Packet: '%s'\n"),
>        if (event->ws.kind () != TARGET_WAITKIND_IGNORE)
>  	break;
>  
> -      /* fall through */
> +      [[fallthrough]];
>      case 'S':		/* Old style status, just signal only.  */
>        {
>  	int sig;
> @@ -8502,7 +8502,7 @@ remote_target::wait_as (ptid_t ptid, target_waitstatus *status,
>  	      putpkt (buf);
>  	      break;
>  	    }
> -	  /* fallthrough */
> +	  [[fallthrough]];
>  	default:
>  	  warning (_("Invalid remote reply: %s"), buf);
>  	  break;
> @@ -9844,7 +9844,7 @@ 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 3725be44276..8849483d4d4 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 bae6737852d..355268dca42 100644
> --- a/gdb/rs6000-tdep.c
> +++ b/gdb/rs6000-tdep.c
> @@ -4247,7 +4247,7 @@ 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,
> @@ -4313,7 +4313,7 @@ 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 */
> @@ -4502,7 +4502,7 @@ 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 */
> @@ -4835,7 +4835,7 @@ 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);
> @@ -4926,7 +4926,7 @@ 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 */
> @@ -5018,7 +5018,7 @@ 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 */
> @@ -5041,7 +5041,7 @@ 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 */
> @@ -5114,7 +5114,7 @@ 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 */
> @@ -5210,7 +5210,7 @@ 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 */
> @@ -5504,7 +5504,7 @@ 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;
> @@ -5728,7 +5728,7 @@ 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 */
> @@ -5822,7 +5822,7 @@ 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 */
> @@ -6009,7 +6009,7 @@ 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 */
> @@ -6032,7 +6032,7 @@ 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
> @@ -6304,7 +6304,7 @@ 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))
> @@ -6350,7 +6350,7 @@ 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);
> @@ -6387,7 +6387,7 @@ 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 */
> @@ -6395,7 +6395,7 @@ 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);
> @@ -6406,7 +6406,7 @@ 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 */
> @@ -7171,10 +7171,10 @@ 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,
> @@ -7184,7 +7184,7 @@ 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);
> @@ -7213,7 +7213,7 @@ 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 */
> @@ -7233,7 +7233,7 @@ 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 */
> @@ -7257,7 +7257,7 @@ 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,
> @@ -7285,7 +7285,7 @@ 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 d2f6008026f..aaf4cef0d7e 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 54b5c89e5e3..5b58cb382e3 100644
> --- a/gdb/s390-tdep.c
> +++ b/gdb/s390-tdep.c
> @@ -4376,7 +4376,7 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  		    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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  		    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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      /* 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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      /* 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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 @@ s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
>  	      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 4011475f7ac..088058030a3 100644
> --- a/gdb/stabsread.c
> +++ b/gdb/stabsread.c
> @@ -1100,7 +1100,7 @@ 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
> @@ -1111,7 +1111,7 @@ 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.  */
> @@ -2499,7 +2499,7 @@ 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 a6236804b08..059922b93ef 100644
> --- a/gdb/symfile.c
> +++ b/gdb/symfile.c
> @@ -3044,7 +3044,7 @@ 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 94a7cafa65b..5adbcfeb544 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 a8760ccf3e4..6521580a1e8 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 7067ae94df0..b4da9675039 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 e4d50d081c9..caefebcaf48 100644
> --- a/gdb/windows-nat.c
> +++ b/gdb/windows-nat.c
> @@ -2286,14 +2286,14 @@ 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 829fc1f09c7..856fa134ed7 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 ae328550b06..f0cc7c0d917 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 4defd79eee4..10d8d280b98 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 932a11888b0..c09fd504270 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 6e5a3cb6603..85d1f9a8905 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':

OK for the arm and aarch64 parts.
  

>>>>> "John" == John Baldwin <jhb@FreeBSD.org> writes:

John> On 10/16/23 4:02 PM, Tom Tromey wrote:
>> 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

John> The fbsd-nat.c change is explicitly ok with me.

I added your approved-by.

Tom
  

...

Luis> OK for the arm and aarch64 parts.

I added your approved-by.

Tom