Use fallthrough attribute.

Use __attribute__ ((fallthrough)) to indicate switch case fall through
instead of a comment. This ensures that the fallthrough warning is not
triggered even if the file is pre-processed (hence stripping the
comments) before it is compiled.

The actual fallback implementation is hidden behind a FALLBACK macro in
case the compiler doesn't support it.

Finally, the -Wimplict-fallthrough warning was upgraded to only allow
the attribute to satisfy it; a comment alone is no longer sufficient.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>

7 files changed, 27 insertions, 12 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index a0bb7a25..a490705f 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,18 @@
+2018-02-09  Joshua Watt  <JPEWhacker@gmail.com>
+
+	* addr2line.c (handle_address): Use FALLTHROUGH macro instead of
+	comment.
+	* elfcompress.c (parse_opt): Likewise.
+	* elflint.c (check_dynamic): Likewise.
+	(check_sections): Likewise.
+	(check_note_data): Likewise.
+	* objdump.c (parse_opt): Likewise.
+	* readelf.c (parse_opt): Likewise.
+	(attr_callback): Likewise.
+	(handle_auxv_note): Likewise.
+	* strings.c (parse_opt): Likewise.
+	* backtrace.c (callback_verify): Likewise.
+
 2018-01-25  Mark Wielaard  <mark@klomp.org>
 
 	* readelf.c (print_debug_ranges_section): Initialize cu to last_cu.
diff --git a/src/addr2line.c b/src/addr2line.c
index ba414a74..444ee52c 100644
--- a/src/addr2line.c
+++ b/src/addr2line.c
@@ -618,7 +618,7 @@ handle_address (const char *string, Dwfl *dwfl)
 	case 1:
 	  addr = 0;
 	  j = i;
-	  /* Fallthrough */
+	  FALLTHROUGH;
 	case 2:
 	  if (string[j] != '\0')
 	    break;
diff --git a/src/elfcompress.c b/src/elfcompress.c
index 8e0d5c55..25378a45 100644
--- a/src/elfcompress.c
+++ b/src/elfcompress.c
@@ -149,7 +149,7 @@ parse_opt (int key, char *arg __attribute__ ((unused)),
 		    N_("Only one input file allowed together with '-o'"));
       /* We only use this for checking the number of arguments, we don't
 	 actually want to consume them.  */
-      /* Fallthrough */
+      FALLTHROUGH;
     default:
       return ARGP_ERR_UNKNOWN;
     }
diff --git a/src/elflint.c b/src/elflint.c
index 51e53c23..df1b3a03 100644
--- a/src/elflint.c
+++ b/src/elflint.c
@@ -1764,7 +1764,7 @@ section [%2d] '%s': entry %zu: pointer does not match address of section [%2d] '
 	  if (dyn->d_tag < DT_ADDRRNGLO || dyn->d_tag > DT_ADDRRNGHI)
 	    /* Value is no pointer.  */
 	    break;
-	  /* FALLTHROUGH */
+	  FALLTHROUGH;
 
 	case DT_AUXILIARY:
 	case DT_FILTER:
@@ -3993,7 +3993,7 @@ section [%2zu] '%s': merge flag set but entry size is zero\n"),
 	    case SHT_NOBITS:
 	      if (is_debuginfo)
 		break;
-	      /* Fallthrough */
+	      FALLTHROUGH;
 	    default:
 	      ERROR (gettext ("\
 section [%2zu] '%s' has unexpected type %d for an executable section\n"),
@@ -4137,7 +4137,7 @@ section [%2zu] '%s': ELF header says this is the section header string table but
 	    ERROR (gettext ("\
 section [%2zu] '%s': relocatable files cannot have dynamic symbol tables\n"),
 		   cnt, section_name (ebl, cnt));
-	  /* FALLTHROUGH */
+	  FALLTHROUGH;
 	case SHT_SYMTAB:
 	  check_symtab (ebl, ehdr, shdr, cnt);
 	  break;
@@ -4336,7 +4336,7 @@ section [%2d] '%s': unknown core file note type %" PRIu32
 	    if (nhdr.n_namesz == sizeof "Linux"
 		&& !memcmp (data->d_buf + name_offset, "Linux", sizeof "Linux"))
 	      break;
-	    /* Fallthrough */
+	    FALLTHROUGH;
 	  default:
 	    if (shndx == 0)
 	      ERROR (gettext ("\
diff --git a/src/objdump.c b/src/objdump.c
index 860cfac6..0dd9a6aa 100644
--- a/src/objdump.c
+++ b/src/objdump.c
@@ -223,7 +223,7 @@ parse_opt (int key, char *arg,
 	}
       /* We only use this for checking the number of arguments, we don't
 	 actually want to consume them.  */
-      /* Fallthrough */
+      FALLTHROUGH;
     default:
       return ARGP_ERR_UNKNOWN;
     }
diff --git a/src/readelf.c b/src/readelf.c
index 6c49d305..d606cf5a 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -480,7 +480,7 @@ parse_opt (int key, char *arg,
 	  print_string_sections = true;
 	  break;
 	}
-      /* Fall through.  */
+      FALLTHROUGH;
     case 'x':
       add_dump_section (arg, false);
       any_control_option = true;
@@ -6081,7 +6081,7 @@ attr_callback (Dwarf_Attribute *attrp, void *arg)
 			dwarf_form_name (form), (uintmax_t) num);
 	      return DWARF_CB_OK;
 	    }
-	  /* else fallthrough */
+	  FALLTHROUGH;
 
 	/* These cases always take a loclistptr and no constant. */
 	case DW_AT_location:
@@ -6269,7 +6269,7 @@ attr_callback (Dwarf_Attribute *attrp, void *arg)
 	      print_block (block.length, block.data);
 	      break;
 	    }
-	  /* Fall through.  */
+	  FALLTHROUGH;
 
 	case DW_AT_location:
 	case DW_AT_data_location:
@@ -9326,7 +9326,7 @@ handle_auxv_note (Ebl *ebl, Elf *core, GElf_Word descsz, GElf_Off desc_pos)
 		printf ("    %s\n", name);
 		break;
 	      }
-	    /* Fall through */
+	    FALLTHROUGH;
 	  case 'x':		/* hex */
 	  case 'p':		/* address */
 	  case 's':		/* address of string */
diff --git a/src/strings.c b/src/strings.c
index d214356c..03d0f133 100644
--- a/src/strings.c
+++ b/src/strings.c
@@ -246,7 +246,7 @@ parse_opt (int key, char *arg,
 	case 'b':
 	case 'B':
 	  big_endian = true;
-	  /* FALLTHROUGH */
+	  FALLTHROUGH;
 
 	case 'l':
 	case 'L':