GAS: Update the .section directive so that a numeric section index can be provided when the "o" flag is used.

	PR 26253
gas	* config/obj-elf.c (obj_elf_section): Accept a numeric value for
	the "o" section flag.  Interpret it as a section index.  Allow an
	index of zero.
	* doc/as.texi: Document the new behaviour.
	* NEWS: Mention the new feature.  Tidy entries.
	* testsuite/gas/elf/sh-link-zero.s: New test.
	* testsuite/gas/elf/sh-link-zero.d: New test driver.
	* testsuite/gas/elf/elf.exp: Run the new test.
	* testsuite/gas/elf/section21.l: Updated expected assembler
	output.

bfd	* elf.c (_bfd_elf_setup_sections): Do not complain about an
	sh_link value of zero when the SLF_LINK_ORDER flag is set.
	(assign_section_numbers): Likewise.

9 files changed, 86 insertions, 33 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index 866a8b4..56796ff 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,17 @@
+2020-10-05  Nick Clifton  <nickc@redhat.com>
+
+	PR 26253
+	* config/obj-elf.c (obj_elf_section): Accept a numeric value for
+	the "o" section flag.  Interpret it as a section index.  Allow an
+	index of zero.
+	* doc/as.texi: Document the new behaviour.
+	* NEWS: Mention the new feature.  Tidy entries.
+	* testsuite/gas/elf/sh-link-zero.s: New test.
+	* testsuite/gas/elf/sh-link-zero.d: New test driver.
+	* testsuite/gas/elf/elf.exp: Run the new test.
+	* testsuite/gas/elf/section21.l: Updated expected assembler
+	output.
+
 2020-10-03  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR gas/26685
diff --git a/gas/NEWS b/gas/NEWS
index 8394f74..8f83beb 100644
--- a/gas/NEWS
+++ b/gas/NEWS
@@ -1,21 +1,12 @@
 -*- text -*-
-* Add support for Cortex-A78 and Cortex-A78AE for ARM.
+* When setting the link order attribute of ELF sections, it is now possible to
+  use a numeric section index instead of symbol name.
 
-* Add support for Cortex-A78 and Cortex-A78AE for AArch64.
+* Add support for Cortex-A78, Cortex-A78AE and Cortex-X1 for AArch64 and ARM.
+  Add support for Cortex-R82, Neoverse V1, and Neoverse N2 for ARM.
 
-* Add support for ETMv4 (Embedded Trace Macrocell) system registers for
-  AArch64.
-
-* Add support for ETE (Embedded Trace Extension) system registers for AArch64.
-
-* Add support for TRBE (Trace Buffer Extension) system registers for AArch64.
-
-* Add support for Cortex-X1 for AArch64.
-
-* Add support for Cortex-X1 for ARM.
-
-* Add support for Arm's Cortex-R82, Neoverse V1, and Neoverse N2
-  processors.
+* Add support for ETMv4 (Embedded Trace Macrocell), ETE (Embedded Trace
+  Extension) and TRBE (Trace Buffer Extension) system registers for AArch64.
 
 * Add support for Armv8-R AArch64.
 
diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
index 45de821..f061ea6 100644
--- a/gas/config/obj-elf.c
+++ b/gas/config/obj-elf.c
@@ -519,8 +519,10 @@ struct section_stack
 
 static struct section_stack *section_stack;
 
+/* Return TRUE iff SEC matches the section info INF.  */
+
 static bfd_boolean
-get_section (bfd *abfd ATTRIBUTE_UNUSED, asection *sec, void *inf)
+get_section_by_match (bfd *abfd ATTRIBUTE_UNUSED, asection *sec, void *inf)
 {
   struct elf_section_match *match = (struct elf_section_match *) inf;
   const char *gname = match->group_name;
@@ -602,7 +604,7 @@ obj_elf_change_section (const char *name,
   previous_section = now_seg;
   previous_subsection = now_subseg;
 
-  old_sec = bfd_get_section_by_name_if (stdoutput, name, get_section,
+  old_sec = bfd_get_section_by_name_if (stdoutput, name, get_section_by_match,
 					(void *) match_p);
   if (old_sec)
     {
@@ -1076,6 +1078,7 @@ obj_elf_section (int push)
   int linkonce;
   subsegT new_subsection = -1;
   struct elf_section_match match;
+  unsigned long linked_to_section_index = -1UL;
 
   if (flag_mri)
     {
@@ -1215,15 +1218,24 @@ obj_elf_section (int push)
 
 	  if ((attr & SHF_LINK_ORDER) != 0 && *input_line_pointer == ',')
 	    {
-	      char c;
-	      unsigned int length;
 	      ++input_line_pointer;
 	      SKIP_WHITESPACE ();
-	      c = get_symbol_name (& beg);
-	      (void) restore_line_pointer (c);
-	      length = input_line_pointer - beg;
-	      if (length)
-		match.linked_to_symbol_name = xmemdup0 (beg, length);
+	      /* Check for a numeric section index, rather than a symbol name.  */
+	      if (ISDIGIT (* input_line_pointer))
+		{
+		  linked_to_section_index = strtoul (input_line_pointer, & input_line_pointer, 0);
+		}
+	      else
+		{
+		  char c;
+		  unsigned int length;
+
+		  c = get_symbol_name (& beg);
+		  (void) restore_line_pointer (c);
+		  length = input_line_pointer - beg;
+		  if (length)
+		    match.linked_to_symbol_name = xmemdup0 (beg, length);
+		}
 	    }
 
 	  if ((attr & SHF_GROUP) != 0 && is_clone)
@@ -1231,6 +1243,7 @@ obj_elf_section (int push)
 	      as_warn (_("? section flag ignored with G present"));
 	      is_clone = FALSE;
 	    }
+
 	  if ((attr & SHF_GROUP) != 0 && *input_line_pointer == ',')
 	    {
 	      ++input_line_pointer;
@@ -1289,6 +1302,7 @@ obj_elf_section (int push)
 	  if (*input_line_pointer == ',')
 	    {
 	      char *save = input_line_pointer;
+
 	      ++input_line_pointer;
 	      SKIP_WHITESPACE ();
 	      if (strncmp (input_line_pointer, "unique", 6) == 0)
@@ -1394,6 +1408,13 @@ obj_elf_section (int push)
     }
   elf_section_flags (now_seg) |= gnu_attr;
 
+  if (linked_to_section_index != -1UL)
+    {
+      elf_section_flags (now_seg) |= SHF_LINK_ORDER;
+      elf_section_data (now_seg)->this_hdr.sh_link = linked_to_section_index;
+      /* FIXME: Should we perform some sanity checking on the section index ?  */
+    }
+
   if (push && new_subsection != -1)
     subseg_set (now_seg, new_subsection);
 }
diff --git a/gas/config/obj-elf.h b/gas/config/obj-elf.h
index b39a1a1..4f29572 100644
--- a/gas/config/obj-elf.h
+++ b/gas/config/obj-elf.h
@@ -104,11 +104,11 @@ struct elf_obj_sy
    field.  */
 struct elf_section_match
 {
-  const char *group_name;
-  const char *linked_to_symbol_name;
-  unsigned int info;
-  unsigned int section_id;
-  flagword flags;
+  const char *   group_name;
+  const char *   linked_to_symbol_name;
+  unsigned int   info;
+  unsigned int   section_id;
+  flagword       flags;
 };
 
 #define OBJ_SYMFIELD_TYPE struct elf_obj_sy
diff --git a/gas/doc/as.texi b/gas/doc/as.texi
index c0baa94..2ba101c 100644
--- a/gas/doc/as.texi
+++ b/gas/doc/as.texi
@@ -6728,11 +6728,14 @@ If @var{flags} contains the @code{o} flag, then the @var{type} argument
 must be present along with an additional field like this:
 
 @smallexample
-.section @var{name},"@var{flags}"o,@@@var{type},@var{SymbolName}
+.section @var{name},"@var{flags}"o,@@@var{type},@var{SymbolName}|@var{SectionIndex}
 @end smallexample
 
 The @var{SymbolName} field specifies the symbol name which the section
-references.
+references.  Alternatively a numeric @var{SectionIndex} can be provided.  This
+is not generally a good idea as section indicies 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 the @var{M} and @var{o} flags are present, then the fields
 for the Merge flag should come first, like this:
diff --git a/gas/testsuite/gas/elf/elf.exp b/gas/testsuite/gas/elf/elf.exp
index 5ce9691..9d75154 100644
--- a/gas/testsuite/gas/elf/elf.exp
+++ b/gas/testsuite/gas/elf/elf.exp
@@ -142,7 +142,7 @@ if { [is_elf_format] } then {
 
     run_dump_test "attach-1"
     run_dump_test "attach-err"
-    
+
     switch -glob $target_triplet {
 	hppa64*-*-hpux* { }
 	riscv*-*-* { }
@@ -261,6 +261,8 @@ if { [is_elf_format] } then {
     run_dump_test "section19"
     run_dump_test "section20"
     run_dump_test "section21"
+    run_dump_test "sh-link-zero"
+
     run_dump_test "dwarf2-1" $dump_opts
     run_dump_test "dwarf2-2" $dump_opts
     run_dump_test "dwarf2-3" $dump_opts
diff --git a/gas/testsuite/gas/elf/section21.l b/gas/testsuite/gas/elf/section21.l
index 50342ec..53f0415 100644
--- a/gas/testsuite/gas/elf/section21.l
+++ b/gas/testsuite/gas/elf/section21.l
@@ -1,5 +1,5 @@
 [^:]*: Assembler messages:
-[^:]*:11: Error: junk at end of line, first unrecognized character is `1'
+[^:]*:11: Error: junk at end of line, first unrecognized character is `f'
 #...
 [^:]*: Error: undefined linked-to symbol `bar' on section `__patchable_function_entries'
 [^:]*: Error: undefined linked-to symbol `foo' on section `__patchable_function_entries'
diff --git a/gas/testsuite/gas/elf/sh-link-zero.d b/gas/testsuite/gas/elf/sh-link-zero.d
new file mode 100644
index 0000000..243d50c
--- /dev/null
+++ b/gas/testsuite/gas/elf/sh-link-zero.d
@@ -0,0 +1,9 @@
+#readelf: --wide --sections
+#name: Setting the sh_link field to 0
+#source: sh-link-zero.s
+
+#...
+.*\.meta1.*WAL[ 	]+0.*
+#...
+.*\.meta2.*WAL[ 	]+[1-9].*
+#pass
diff --git a/gas/testsuite/gas/elf/sh-link-zero.s b/gas/testsuite/gas/elf/sh-link-zero.s
new file mode 100644
index 0000000..9e90792
--- /dev/null
+++ b/gas/testsuite/gas/elf/sh-link-zero.s
@@ -0,0 +1,13 @@
+.section .meta1,"awo",%progbits,0
+1:
+	.dc.b 0
+
+.section .meta2,"awo",%progbits,foo
+2:
+	.dc.b 1
+
+.section foo, "aw"
+	.dc.b 2
+
+.section .gc_root,"a",%progbits
+	.dc.a 1b