gas/ELF: allow specifying entity size for arbitrary sections

The spec doesn't tie entity size to just SHF_MERGE and SHF_STRINGS
sections. Introduce a new "section letter" 'E' to allow recording (and
checking) of entity size even without 'M' or 'S'.

bfd/elf.c

@@ -869,20 +869,16 @@ _bfd_elf_make_section_from_shdr (bfd *abfd,
   else if ((flags & SEC_LOAD) != 0)
     flags |= SEC_DATA;
   if ((hdr->sh_flags & SHF_MERGE) != 0)
-    {
-      flags |= SEC_MERGE;
-      newsect->entsize = hdr->sh_entsize;
-    }
+    flags |= SEC_MERGE;
   if ((hdr->sh_flags & SHF_STRINGS) != 0)
-    {
-      flags |= SEC_STRINGS;
-      newsect->entsize = hdr->sh_entsize;
-    }
+    flags |= SEC_STRINGS;
   if ((hdr->sh_flags & SHF_TLS) != 0)
     flags |= SEC_THREAD_LOCAL;
   if ((hdr->sh_flags & SHF_EXCLUDE) != 0)
     flags |= SEC_EXCLUDE;
 
+  newsect->entsize = hdr->sh_entsize;
+
   switch (elf_elfheader (abfd)->e_ident[EI_OSABI])
     {
       /* FIXME: We should not recognize SHF_GNU_MBIND for ELFOSABI_NONE,
@@ -3770,6 +3766,9 @@ elf_fake_sections (bfd *abfd, asection *asect, void *fsarg)
   if ((asect->flags & (SEC_GROUP | SEC_EXCLUDE)) == SEC_EXCLUDE)
     this_hdr->sh_flags |= SHF_EXCLUDE;
 
+  if (this_hdr->sh_entsize == 0)
+    this_hdr->sh_entsize = asect->entsize;
+
   /* If the section has relocs, set up a section header for the
      SHT_REL[A] section.  If two relocation sections are required for
      this section, it is up to the processor-specific back-end to

gas/NEWS

@@ -1,5 +1,8 @@
 -*- text -*-
 
+* ELF targets can now have section entity size specified for arbitrary
+  sections, using the new attribute letter 'E'.
+
 * NaCl target support is removed.
 
 Changes in 2.45:

gas/config/obj-elf.c

@@ -792,7 +792,7 @@ change_section (const char *name,
 	= match_p->linked_to_symbol_name;
 
       bfd_set_section_flags (sec, flags);
-      if (flags & (SEC_MERGE | SEC_STRINGS))
+      if (entsize != 0)
 	sec->entsize = entsize;
       elf_group_name (sec) = match_p->group_name;
 
@@ -847,7 +847,7 @@ change_section (const char *name,
 	       processor or application specific attribute as suspicious?  */
 	    elf_section_flags (sec) = attr;
 
-	  if ((flags & (SEC_MERGE | SEC_STRINGS))
+	  if (entsize != 0
 	      && old_sec->entsize != (unsigned) entsize)
 	    as_bad (_("changed section entity size for %s"), name);
 	}
@@ -871,7 +871,8 @@ obj_elf_change_section (const char *name,
 
 static bfd_vma
 obj_elf_parse_section_letters (char *str, size_t len, bool push,
-			       bool *is_clone, int *inherit, bfd_vma *gnu_attr)
+			       bool *is_clone, int *inherit, bfd_vma *gnu_attr,
+			       bool *has_entsize)
 {
   bfd_vma attr = 0;
 
@@ -913,6 +914,9 @@ obj_elf_parse_section_letters (char *str, size_t len, bool push,
 	case 'x':
 	  attr |= SHF_EXECINSTR;
 	  break;
+	case 'E':
+	  *has_entsize = true;
+	  break;
 	case 'G':
 	  attr |= SHF_GROUP;
 	  break;
@@ -978,8 +982,8 @@ obj_elf_parse_section_letters (char *str, size_t len, bool push,
 		{
 		  as_bad (_("unrecognized .%ssection attribute: want %s%s%s,? or number"),
 		    push ? "push" : "",
-		    gnu_attr != NULL ? "a,d,e,o,w,x,G,M,R,S,T"
-				     : "a,e,o,w,x,G,M,S,T",
+		    gnu_attr != NULL ? "a,d,e,o,w,x,E,G,M,R,S,T"
+				     : "a,e,o,w,x,E,G,M,S,T",
 		    md_extra != NULL ? "," : "", md_extra);
 		  return attr;
 		}
@@ -1187,7 +1191,7 @@ obj_elf_section (int push)
   bfd_vma attr;
   bfd_vma gnu_attr;
   int entsize;
-  bool linkonce;
+  bool linkonce, has_entsize;
   subsegT new_subsection = 0;
   struct elf_section_match match;
   unsigned long linked_to_section_index = -1UL;
@@ -1232,6 +1236,7 @@ obj_elf_section (int push)
   attr = 0;
   gnu_attr = 0;
   entsize = 0;
+  has_entsize = false;
   linkonce = 0;
 
   if (*input_line_pointer == ',')
@@ -1276,7 +1281,8 @@ obj_elf_section (int push)
 						    == ELFOSABI_GNU)
 						|| (bed->elf_osabi
 						    == ELFOSABI_FREEBSD)
-						? &gnu_attr : NULL);
+						? &gnu_attr : NULL,
+						&has_entsize);
 
 	  if (inherit > 0)
 	    attr |= elf_section_flags (now_seg);
@@ -1285,6 +1291,9 @@ obj_elf_section (int push)
 	  if (inherit)
 	    type = elf_section_type (now_seg);
 
+	  if ((attr & (SHF_MERGE | SHF_STRINGS)) != 0)
+	    has_entsize = true;
+
 	  SKIP_WHITESPACE ();
 	  if (*input_line_pointer == ',')
 	    {
@@ -1324,16 +1333,18 @@ obj_elf_section (int push)
 	    }
 
 	  SKIP_WHITESPACE ();
-	  if ((attr & (SHF_MERGE | SHF_STRINGS)) != 0
-	      && *input_line_pointer == ',')
+	  if (has_entsize && *input_line_pointer == ',')
 	    {
 	      ++input_line_pointer;
 	      SKIP_WHITESPACE ();
 	      if (inherit && *input_line_pointer == ','
+		  && ((bfd_section_flags (now_seg)
+		       & (SEC_MERGE | SEC_STRINGS)) != 0
+		      || now_seg->entsize))
+		goto fetch_entsize;
+	      if (is_end_of_stmt (*input_line_pointer)
 		  && (bfd_section_flags (now_seg)
 		      & (SEC_MERGE | SEC_STRINGS)) != 0)
-		goto fetch_entsize;
-	      if (is_end_of_stmt (*input_line_pointer))
 		{
 		  /* ??? This is here for older versions of gcc that
 		     test for gas string merge support with
@@ -1341,7 +1352,7 @@ obj_elf_section (int push)
 		     Unfortunately '@' begins a comment on arm.
 		     This isn't as_warn because gcc tests with
 		     --fatal-warnings. */
-		  as_tsktsk (_("missing merge / string entity size, 1 assumed"));
+		  as_tsktsk (_("missing section entity size, 1 assumed"));
 		  entsize = 1;
 		}
 	      else
@@ -1350,15 +1361,17 @@ obj_elf_section (int push)
 		  SKIP_WHITESPACE ();
 		  if (entsize <= 0)
 		    {
-		      as_warn (_("invalid merge / string entity size"));
+		      as_warn (_("invalid section entity size"));
 		      attr &= ~(SHF_MERGE | SHF_STRINGS);
+		      has_entsize = false;
 		      entsize = 0;
 		    }
 		}
 	    }
-	  else if ((attr & (SHF_MERGE | SHF_STRINGS)) != 0 && inherit
-		    && (bfd_section_flags (now_seg)
-			& (SEC_MERGE | SEC_STRINGS)) != 0)
+	  else if (has_entsize && inherit
+		    && ((bfd_section_flags (now_seg)
+			 & (SEC_MERGE | SEC_STRINGS)) != 0
+			|| now_seg->entsize))
 	    {
 	    fetch_entsize:
 	      entsize = now_seg->entsize;
@@ -1369,6 +1382,7 @@ obj_elf_section (int push)
 		 entsize must be specified if SHF_MERGE is set.  */
 	      as_warn (_("entity size for SHF_MERGE not specified"));
 	      attr &= ~(SHF_MERGE | SHF_STRINGS);
+	      has_entsize = false;
 	    }
 	  else if ((attr & SHF_STRINGS) != 0)
 	    {
@@ -1378,6 +1392,11 @@ obj_elf_section (int push)
 		 compatibility.  */
 	      entsize = 1;
 	    }
+	  else if (has_entsize)
+	    {
+	      as_warn (_("entity size not specified"));
+	      has_entsize = false;
+	    }
 
 	  if ((attr & (SHF_MERGE | SHF_STRINGS)) != 0 && type == SHT_NOBITS)
 	    as_warn (_("bogus SHF_MERGE / SHF_STRINGS for SHT_NOBITS section"));

gas/doc/as.texi

@@ -7004,12 +7004,14 @@ section) in the same file.
 section is writable
 @item x
 section is executable
+@item E
+section has a (non-zero) element/entry size
+@item G
+section is a member of a section group
 @item M
 section is mergeable
 @item S
 section contains zero terminated strings
-@item G
-section is a member of a section group
 @item T
 section is used for thread-local-storage
 @item ?
@@ -7118,8 +7120,8 @@ is not generally a good idea as section indices are rarely known at assembly
 time, but the facility is provided for testing purposes.  An index of zero is
 allowed.  It indicates that the linked-to section has already been discarded.
 
-Note: If both one of @var{M} or @var{S} and @var{o} flags are present, then the
-fields for the Merge/String flag should come first, like this:
+Note: If both one of @var{M}, @var{S}, or @var{E} and @var{o} flags are present,
+then the type and entry size fields should come first, like this:
 
 @smallexample
 .section @var{name},"@var{flags}"Mo,@@@var{type},@var{entsize},@var{SymbolName}
@@ -7142,8 +7144,8 @@ indicates that only one copy of this section should be retained
 an alias for comdat
 @end table
 
-Note: Uf both one of @var{M} or @var{S} and @var{G} flags are present then the
-fields for the Merge/String flag should come first, like this:
+Note: If both one of @var{M}, @var{S}, or @var{E} and @var{G} flags are present
+then the type and entry size fields should come first, like this:
 
 @smallexample
 .section @var{name} , "@var{flags}"MG, @@@var{type}, @var{entsize}, @var{GroupName}[, @var{linkage}]

gas/testsuite/gas/elf/elf.exp

@@ -293,6 +293,7 @@ if { [is_elf_format] } then {
     run_dump_test "sh-link-zero"
     run_dump_test "string"
     run_dump_test "size"
+    run_dump_test "entsize"
     run_dump_test "dwarf2-1" $dump_opts
     run_dump_test "dwarf2-2" $dump_opts
     run_dump_test "dwarf2-3" $dump_opts

gas/testsuite/gas/elf/entsize.d

@@ -0,0 +1,9 @@
+#readelf: -SW
+#name: sections with entity size
+
+#...
+[ 	]*\[.*\][ 	]+\.merge[ 	]+PROGBITS[ 	]+0+[ 	]+[0-9a-f]+[ 	]+0+18[ 	]+0c[ 	]+AM[ 	].*
+[ 	]*\[.*\][ 	]+\.string[ 	]+PROGBITS[ 	]+0+[ 	]+[0-9a-f]+[ 	]+0+6[ 	]+02[ 	]+AS[ 	].*
+[ 	]*\[.*\][ 	]+\.custom[ 	]+PROGBITS[ 	]+0+[ 	]+[0-9a-f]+[ 	]+0+c[ 	]+06[ 	]+A[ 	].*
+[ 	]*\[.*\][ 	]+\.bss\.custom[ 	]+NOBITS[ 	]+0+[ 	]+[0-9a-f]+[ 	]+0+1e[ 	]+06[ 	]+WA[ 	].*
+#pass

gas/testsuite/gas/elf/entsize.s

@@ -0,0 +1,8 @@
+	.section .merge, "aM", 12
+	.dc.l 1, 2, 3, 4, 5, 6
+	.section .string, "aS", %progbits, 2
+	.dc.w 0x0020, 0x0021, 0x0022
+	.section .custom, "aE", 6
+	.dc.w 5, 6, 7, 8, 9, 0
+	.section .bss.custom, "awE", %nobits, 6
+	.skip 30