Add fall-through comments.

This patch adds fall-through comments in some cases where -Wextra
produces implicit-fallthrough warnings.

The patch is non-exhaustive.  Apart from architecture-specific code
for non-x86_64 architectures, it does not change sunrpc/xdr.c (legacy
code, probably should have such changes, but left to be dealt with
separately), or places that already had comments about the
fall-through but not matching the form expected by
-Wimplicit-fallthrough=3 (the default level with -Wextra; my
inclination is to adjust those comments to match rather than
downgrading to -Wimplicit-fallthrough=1 to allow any comment), or one
place where I thought the implicit fallthrough was not correct and so
should be handled separately as a bug fix.  I think the key thing to
consider in review of this patch is whether the fall-through is indeed
intended and correct in each place where such a comment is added.

Tested for x86_64.

	* elf/dl-exception.c (_dl_exception_create_format): Add
	fall-through comments.
	* elf/ldconfig.c (parse_conf_include): Likewise.
	* elf/rtld.c (print_statistics): Likewise.
	* locale/programs/charmap.c (parse_charmap): Likewise.
	* misc/mntent_r.c (__getmntent_r): Likewise.
	* posix/wordexp.c (parse_arith): Likewise.
	(parse_backtick): Likewise.
	* resolv/ns_ttl.c (ns_parse_ttl): Likewise.
	* sysdeps/x86/cpu-features.c (init_cpu_features): Likewise.
	* sysdeps/x86_64/dl-machine.h (elf_machine_rela): Likewise.

ChangeLog

@@ -1,3 +1,17 @@
+2019-02-12  Joseph Myers  <joseph@codesourcery.com>
+
+	* elf/dl-exception.c (_dl_exception_create_format): Add
+	fall-through comments.
+	* elf/ldconfig.c (parse_conf_include): Likewise.
+	* elf/rtld.c (print_statistics): Likewise.
+	* locale/programs/charmap.c (parse_charmap): Likewise.
+	* misc/mntent_r.c (__getmntent_r): Likewise.
+	* posix/wordexp.c (parse_arith): Likewise.
+	(parse_backtick): Likewise.
+	* resolv/ns_ttl.c (ns_parse_ttl): Likewise.
+	* sysdeps/x86/cpu-features.c (init_cpu_features): Likewise.
+	* sysdeps/x86_64/dl-machine.h (elf_machine_rela): Likewise.
+
 2019-02-11  Paul A. Clarke  <pc@us.ibm.com>
 
 	* sysdeps/powerpc/fpu/e_sqrt.c (__slow_ieee754_sqrtf):

elf/dl-exception.c

@@ -123,6 +123,7 @@ _dl_exception_create_format (struct dl_exception *exception, const char *objname
 		  ++p;
 		  break;
 		}
+	      /* Fall through.  */
 	    case 'x':
 	      length += INT_WIDTH / 4;
 	      break;

elf/ldconfig.c

@@ -1228,6 +1228,7 @@ parse_conf_include (const char *config_file, unsigned int lineno,
 
     case GLOB_NOSPACE:
       errno = ENOMEM;
+      /* Fall through.  */
     case GLOB_ABORTED:
       if (opt_verbose)
 	error (0, errno, _("%s:%u: cannot read directory %s"),

elf/rtld.c

@@ -2738,8 +2738,10 @@ print_statistics (hp_timing_t *rtld_total_timep)
 	{
 	case 3:
 	  *wp++ = *cp++;
+	  /* Fall through.  */
 	case 2:
 	  *wp++ = *cp++;
+	  /* Fall through.  */
 	case 1:
 	  *wp++ = '.';
 	  *wp++ = *cp++;
@@ -2801,8 +2803,10 @@ print_statistics (hp_timing_t *rtld_total_timep)
 	{
 	case 3:
 	  *wp++ = *cp++;
+	  /* Fall through.  */
 	case 2:
 	  *wp++ = *cp++;
+	  /* Fall through.  */
 	case 1:
 	  *wp++ = '.';
 	  *wp++ = *cp++;

locale/programs/charmap.c

@@ -713,6 +713,7 @@ only WIDTH definitions are allowed to follow the CHARMAP definition"));
 	      state = 95;
 	      continue;
 	    }
+	  /* Fall through.  */
 
 	case 96:
 	  if (nowtok != tok_number)

misc/mntent_r.c

@@ -174,8 +174,10 @@ __getmntent_r (FILE *stream, struct mntent *mp, char *buffer, int bufsiz)
     {
     case 0:
       mp->mnt_freq = 0;
+      /* Fall through.  */
     case 1:
       mp->mnt_passno = 0;
+      /* Fall through.  */
     case 2:
       break;
     }

posix/wordexp.c

@@ -799,6 +799,7 @@ parse_arith (char **word, size_t *word_length, size_t *max_length,
 
 	case '(':
 	  ++paren_depth;
+	  /* Fall through.  */
 	default:
 	  expr = w_addchar (expr, &expr_length, &expr_maxlen, words[*offset]);
 	  if (expr == NULL)
@@ -2127,6 +2128,7 @@ parse_backtick (char **word, size_t *word_length, size_t *max_length,
 
 	case '\'':
 	  squoting = 1 - squoting;
+	  /* Fall through.  */
 	default:
 	  comm = w_addchar (comm, &comm_length, &comm_maxlen, words[*offset]);
 	  if (comm == NULL)

resolv/ns_ttl.c

@@ -113,9 +113,13 @@ ns_parse_ttl(const char *src, u_long *dst) {
 			ch = toupper(ch);
 		switch (ch) {
 		case 'W':  tmp *= 7;
+		  /* Fall through.  */
 		case 'D':  tmp *= 24;
+		  /* Fall through.  */
 		case 'H':  tmp *= 60;
+		  /* Fall through.  */
 		case 'M':  tmp *= 60;
+		  /* Fall through.  */
 		case 'S':  break;
 		default:   goto einval;
 		}

sysdeps/x86/cpu-features.c

@@ -375,6 +375,7 @@ init_cpu_features (struct cpu_features *cpu_features)
 		 of Core i3/i5/i7 processors if AVX is available.  */
 	      if (!CPU_FEATURES_CPU_P (cpu_features, AVX))
 		break;
+	      /* Fall through.  */
 
 	    case 0x1a:
 	    case 0x1e:
@@ -402,6 +403,7 @@ init_cpu_features (struct cpu_features *cpu_features)
 	      /* Xeon E7 v3 with stepping >= 4 has working TSX.  */
 	      if (stepping >= 4)
 		break;
+	      /* Fall through.  */
 	    case 0x3c:
 	    case 0x45:
 	    case 0x46:

sysdeps/x86_64/dl-machine.h

@@ -347,6 +347,7 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
 	  /* Set to symbol size plus addend.  */
 	  value = sym->st_size;
 # endif
+	  /* Fall through.  */
 	case R_X86_64_GLOB_DAT:
 	case R_X86_64_JUMP_SLOT:
 	  *reloc_addr = value + reloc->r_addend;
@@ -460,6 +461,7 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
 	  /* Set to symbol size plus addend.  */
 	  value = sym->st_size;
 #  endif
+	  /* Fall through.  */
 	case R_X86_64_32:
 	  value += reloc->r_addend;
 	  *(unsigned int *) reloc_addr = value;