ELF: Support the section flag 'o' in .section directive

As shown in

https://sourceware.org/bugzilla/show_bug.cgi?id=25490

--gc-sections will silently remove __patchable_function_entries section
and generate corrupt result.  This patch adds the section flag 'o' to
.section directive:

.section __patchable_function_entries,"awo",@progbits,foo
.section __patchable_function_entries,"awoG",@progbits,foo,foo,comdat
.section __patchable_function_entries,"awo",@progbits,bar,unique,4
.section __patchable_function_entries,"awoG",@progbits,foo,foo,comdat,unique,1

which specifies the symbol name which the section references.  Assmebler
will set its elf_linked_to_section to a local section where the symbol
is defined.

Linker is updated to call mark_hook if gc_mark of any of its linked-to
sections is set after all sections, except for backend specific ones,
have been garbage collected.

bfd/

	PR gas/25381
	* bfd-in2.h: Regenerated.
	* elflink.c (_bfd_elf_gc_mark_extra_sections): Call mark_hook
	on section if gc_mark of any of its linked-to sections is set
	and don't set gc_mark again.
	* section.c (asection): Add linked_to_symbol_name to map_head
	union.

gas/

	PR gas/25381
	* config/obj-elf.c (get_section): Also check
	linked_to_symbol_name.
	(obj_elf_change_section): Also set map_head.linked_to_symbol_name.
	(obj_elf_parse_section_letters): Handle the 'o' flag.
	(build_group_lists): Renamed to ...
	(build_additional_section_info): This.  Set elf_linked_to_section
	from map_head.linked_to_symbol_name.
	(elf_adjust_symtab): Updated.
	* config/obj-elf.h (elf_section_match): Add linked_to_symbol_name.
	* doc/as.texi: Document the 'o' flag.
	* testsuite/gas/elf/elf.exp: Run PR gas/25381 tests.
	* testsuite/gas/elf/section18.d: New file.
	* testsuite/gas/elf/section18.s: Likewise.
	* testsuite/gas/elf/section19.d: Likewise.
	* testsuite/gas/elf/section19.s: Likewise.
	* testsuite/gas/elf/section20.d: Likewise.
	* testsuite/gas/elf/section20.s: Likewise.
	* testsuite/gas/elf/section21.d: Likewise.
	* testsuite/gas/elf/section21.l: Likewise.
	* testsuite/gas/elf/section21.s: Likewise.

ld/

	PR ld/24526
	PR ld/25021
	PR ld/25490
	* testsuite/ld-elf/elf.exp: Run PR ld/25490 tests.
	* testsuite/ld-elf/pr24526.d: New file.
	* testsuite/ld-elf/pr24526.s: Likewise.
	* testsuite/ld-elf/pr25021.d: Likewise.
	* testsuite/ld-elf/pr25021.s: Likewise.
	* testsuite/ld-elf/pr25490-2-16.rd: Likewise.
	* testsuite/ld-elf/pr25490-2-32.rd: Likewise.
	* testsuite/ld-elf/pr25490-2-64.rd: Likewise.
	* testsuite/ld-elf/pr25490-2.s: Likewise.
	* testsuite/ld-elf/pr25490-3-16.rd: Likewise.
	* testsuite/ld-elf/pr25490-3-32.rd: Likewise.
	* testsuite/ld-elf/pr25490-3-64.rd: Likewise.
	* testsuite/ld-elf/pr25490-3.s: Likewise.
	* testsuite/ld-elf/pr25490-4-16.rd: Likewise.
	* testsuite/ld-elf/pr25490-4-32.rd: Likewise.
	* testsuite/ld-elf/pr25490-4-64.rd: Likewise.
	* testsuite/ld-elf/pr25490-4.s: Likewise.
	* testsuite/ld-elf/pr25490-5-16.rd: Likewise.
	* testsuite/ld-elf/pr25490-5-32.rd: Likewise.
	* testsuite/ld-elf/pr25490-5-64.rd: Likewise.
	* testsuite/ld-elf/pr25490-5.s: Likewise.
	* testsuite/ld-elf/pr25490-6-16.rd: Likewise.
	* testsuite/ld-elf/pr25490-6-32.rd: Likewise.
	* testsuite/ld-elf/pr25490-6-64.rd: Likewise.
	* testsuite/ld-elf/pr25490-6.s: Likewise.

14 files changed, 197 insertions, 5 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index 9fa0350..b600180 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,5 +1,29 @@
 2020-02-06  H.J. Lu  <hongjiu.lu@intel.com>
 
+	PR gas/25381
+	* config/obj-elf.c (get_section): Also check
+	linked_to_symbol_name.
+	(obj_elf_change_section): Also set map_head.linked_to_symbol_name.
+	(obj_elf_parse_section_letters): Handle the 'o' flag.
+	(build_group_lists): Renamed to ...
+	(build_additional_section_info): This.  Set elf_linked_to_section
+	from map_head.linked_to_symbol_name.
+	(elf_adjust_symtab): Updated.
+	* config/obj-elf.h (elf_section_match): Add linked_to_symbol_name.
+	* doc/as.texi: Document the 'o' flag.
+	* testsuite/gas/elf/elf.exp: Run PR gas/25381 tests.
+	* testsuite/gas/elf/section18.d: New file.
+	* testsuite/gas/elf/section18.s: Likewise.
+	* testsuite/gas/elf/section19.d: Likewise.
+	* testsuite/gas/elf/section19.s: Likewise.
+	* testsuite/gas/elf/section20.d: Likewise.
+	* testsuite/gas/elf/section20.s: Likewise.
+	* testsuite/gas/elf/section21.d: Likewise.
+	* testsuite/gas/elf/section21.l: Likewise.
+	* testsuite/gas/elf/section21.s: Likewise.
+
+2020-02-06  H.J. Lu  <hongjiu.lu@intel.com>
+
 	* NEWS: Mention x86 assembler options to align branches for
 	binutils 2.34.
 
diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
index 2958490..d7a07fe 100644
--- a/gas/config/obj-elf.c
+++ b/gas/config/obj-elf.c
@@ -524,6 +524,8 @@ get_section (bfd *abfd ATTRIBUTE_UNUSED, asection *sec, void *inf)
   struct elf_section_match *match = (struct elf_section_match *) inf;
   const char *gname = match->group_name;
   const char *group_name = elf_group_name (sec);
+  const char *linked_to_symbol_name
+    = sec->map_head.linked_to_symbol_name;
   unsigned int info = elf_section_data (sec)->this_hdr.sh_info;
 
   return (info == match->info
@@ -533,7 +535,12 @@ get_section (bfd *abfd ATTRIBUTE_UNUSED, asection *sec, void *inf)
 	  && (group_name == gname
 	      || (group_name != NULL
 		  && gname != NULL
-		  && strcmp (group_name, gname) == 0)));
+		  && strcmp (group_name, gname) == 0))
+	  && (linked_to_symbol_name == match->linked_to_symbol_name
+	      || (linked_to_symbol_name != NULL
+		  && match->linked_to_symbol_name != NULL
+		  && strcmp (linked_to_symbol_name,
+			     match->linked_to_symbol_name) == 0)));
 }
 
 /* Handle the .section pseudo-op.  This code supports two different
@@ -740,6 +747,10 @@ obj_elf_change_section (const char *name,
       sec->section_id = match_p->section_id;
       flags |= match_p->flags;
 
+      /* Set the linked-to symbol name.  */
+      sec->map_head.linked_to_symbol_name
+	= match_p->linked_to_symbol_name;
+
       bfd_set_section_flags (sec, flags);
       if (flags & SEC_MERGE)
 	sec->entsize = entsize;
@@ -801,6 +812,9 @@ obj_elf_parse_section_letters (char *str, size_t len,
 	case 'e':
 	  attr |= SHF_EXCLUDE;
 	  break;
+	case 'o':
+	  attr |= SHF_LINK_ORDER;
+	  break;
 	case 'w':
 	  attr |= SHF_WRITE;
 	  break;
@@ -841,7 +855,7 @@ obj_elf_parse_section_letters (char *str, size_t len,
 	default:
 	  {
 	    const char *bad_msg = _("unrecognized .section attribute:"
-				    " want a,e,w,x,M,S,G,T or number");
+				    " want a,e,o,w,x,M,S,G,T or number");
 #ifdef md_elf_section_letter
 	    bfd_vma md_attr = md_elf_section_letter (*str, &bad_msg);
 	    if (md_attr != (bfd_vma) -1)
@@ -1154,6 +1168,19 @@ obj_elf_section (int push)
 	      attr &= ~SHF_MERGE;
 	    }
 
+	  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);
+	    }
+
 	  if ((attr & SHF_GROUP) != 0 && is_clone)
 	    {
 	      as_warn (_("? section flag ignored with G present"));
@@ -2476,10 +2503,12 @@ static struct group_list groups;
 /* Called via bfd_map_over_sections.  If SEC is a member of a group,
    add it to a list of sections belonging to the group.  INF is a
    pointer to a struct group_list, which is where we store the head of
-   each list.  */
+   each list.  If its link_to_symbol_name isn't NULL, set up its
+   linked-to section.  */
 
 static void
-build_group_lists (bfd *abfd ATTRIBUTE_UNUSED, asection *sec, void *inf)
+build_additional_section_info (bfd *abfd ATTRIBUTE_UNUSED,
+				  asection *sec, void *inf)
 {
   struct group_list *list = (struct group_list *) inf;
   const char *group_name = elf_group_name (sec);
@@ -2487,6 +2516,18 @@ build_group_lists (bfd *abfd ATTRIBUTE_UNUSED, asection *sec, void *inf)
   unsigned int *elem_idx;
   unsigned int *idx_ptr;
 
+  if (sec->map_head.linked_to_symbol_name)
+    {
+      symbolS *linked_to_sym;
+      linked_to_sym = symbol_find (sec->map_head.linked_to_symbol_name);
+      if (!linked_to_sym || !S_IS_DEFINED (linked_to_sym))
+	as_bad (_("undefined linked-to symbol `%s' on section `%s'"),
+		sec->map_head.linked_to_symbol_name,
+		bfd_section_name (sec));
+      else
+	elf_linked_to_section (sec) = S_GET_SEGMENT (linked_to_sym);
+    }
+
   if (group_name == NULL)
     return;
 
@@ -2533,7 +2574,8 @@ elf_adjust_symtab (void)
   groups.num_group = 0;
   groups.head = NULL;
   groups.indexes = hash_new ();
-  bfd_map_over_sections (stdoutput, build_group_lists, &groups);
+  bfd_map_over_sections (stdoutput, build_additional_section_info,
+			 &groups);
 
   /* Make the SHT_GROUP sections that describe each section group.  We
      can't set up the section contents here yet, because elf section
diff --git a/gas/config/obj-elf.h b/gas/config/obj-elf.h
index 7cfcc25..54af9eb 100644
--- a/gas/config/obj-elf.h
+++ b/gas/config/obj-elf.h
@@ -82,6 +82,7 @@ struct elf_obj_sy
 struct elf_section_match
 {
   const char *group_name;
+  const char *linked_to_symbol_name;
   unsigned int info;
   unsigned int section_id;
   flagword flags;
diff --git a/gas/doc/as.texi b/gas/doc/as.texi
index 152bbfd..1554c51 100644
--- a/gas/doc/as.texi
+++ b/gas/doc/as.texi
@@ -6599,6 +6599,9 @@ section is allocatable
 section is a GNU_MBIND section
 @item e
 section is excluded from executable and shared library.
+@item o
+section references a symbol defined in another section (the linked-to
+section) in the same file.
 @item w
 section is writable
 @item x
@@ -6678,6 +6681,23 @@ which is a suffix of a larger string is considered a duplicate.  Thus
 @code{"def"} will be merged with @code{"abcdef"};  A reference to the first
 @code{"def"} will be changed to a reference to @code{"abcdef"+3}.
 
+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}
+@end smallexample
+
+The @var{SymbolName} field specifies the symbol name which the section
+references.
+
+Note: If both the @var{M} and @var{o} flags are present, then the fields
+for the Merge flag should come first, like this:
+
+@smallexample
+.section @var{name},"@var{flags}"Mo,@@@var{type},@var{entsize},@var{SymbolName}
+@end smallexample
+
 If @var{flags} contains the @code{G} symbol then the @var{type} argument must
 be present along with an additional field like this:
 
@@ -6702,6 +6722,13 @@ the Merge flag should come first, like this:
 .section @var{name} , "@var{flags}"MG, @@@var{type}, @var{entsize}, @var{GroupName}[, @var{linkage}]
 @end smallexample
 
+If both @code{o} flag and @code{G} flag are present, then the
+@var{SymbolName} field for @code{o} comes first, like this:
+
+@smallexample
+.section @var{name},"@var{flags}"oG,@@@var{type},@var{SymbolName},@var{GroupName}[,@var{linkage}]
+@end smallexample
+
 If @var{flags} contains the @code{?} symbol then it may not also contain the
 @code{G} symbol and the @var{GroupName} or @var{linkage} fields should not be
 present.  Instead, @code{?} says to consider the section that's current before
diff --git a/gas/testsuite/gas/elf/elf.exp b/gas/testsuite/gas/elf/elf.exp
index 08c6830..0f9b267 100644
--- a/gas/testsuite/gas/elf/elf.exp
+++ b/gas/testsuite/gas/elf/elf.exp
@@ -249,6 +249,10 @@ if { [is_elf_format] } then {
     run_dump_test "section16a"
     run_dump_test "section16b"
     run_dump_test "section17"
+    run_dump_test "section18"
+    run_dump_test "section19"
+    run_dump_test "section20"
+    run_dump_test "section21"
     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/section18.d b/gas/testsuite/gas/elf/section18.d
new file mode 100644
index 0000000..f4f2930
--- /dev/null
+++ b/gas/testsuite/gas/elf/section18.d
@@ -0,0 +1,8 @@
+#readelf: -SW
+#name: linked-to section 1
+
+#...
+ +\[ *[0-9]+\] +__patchable_function_entries +PROGBITS +[0-9a-f]+ +[0-9a-f]+ +0+[248] +00 +WAL +.*
+#...
+ +\[ *[0-9]+\] +__patchable_function_entries +PROGBITS +[0-9a-f]+ +[0-9a-f]+ +0+[248] +00 +WAL +.*
+#pass
diff --git a/gas/testsuite/gas/elf/section18.s b/gas/testsuite/gas/elf/section18.s
new file mode 100644
index 0000000..d51eb68
--- /dev/null
+++ b/gas/testsuite/gas/elf/section18.s
@@ -0,0 +1,13 @@
+	.text
+foo:
+	.section __patchable_function_entries,"awo",%progbits,foo
+	.dc.a	.LPFE1
+	.text
+.LPFE1:
+	.byte 0
+	.section __patchable_function_entries,"awo",%progbits,bar
+	.dc.a	.LPFE2
+	.text
+bar:
+.LPFE2:
+	.byte 0
diff --git a/gas/testsuite/gas/elf/section19.d b/gas/testsuite/gas/elf/section19.d
new file mode 100644
index 0000000..edf2b94
--- /dev/null
+++ b/gas/testsuite/gas/elf/section19.d
@@ -0,0 +1,8 @@
+#readelf: -SW
+#name: linked-to section 2
+
+#...
+ +\[ *[0-9]+\] +__patchable_function_entries +PROGBITS +[0-9a-f]+ +[0-9a-f]+ +0+[248] +00 +WAL +.*
+#...
+ +\[ *[0-9]+\] +__patchable_function_entries +PROGBITS +[0-9a-f]+ +[0-9a-f]+ +0+[248] +00 +WAL +.*
+#pass
diff --git a/gas/testsuite/gas/elf/section19.s b/gas/testsuite/gas/elf/section19.s
new file mode 100644
index 0000000..7d30ea1
--- /dev/null
+++ b/gas/testsuite/gas/elf/section19.s
@@ -0,0 +1,13 @@
+	.section .text,"ax",%progbits,unique,20
+foo:
+	.section __patchable_function_entries,"awo",%progbits,foo,unique,2
+	.dc.a	.LPFE1
+	.section .text,"ax",%progbits,unique,20
+.LPFE1:
+	.byte 0
+	.section __patchable_function_entries,"awo",%progbits,bar,unique,102
+	.dc.a	.LPFE2
+	.section .text,"ax",%progbits,unique,2
+bar:
+.LPFE2:
+	.byte 0
diff --git a/gas/testsuite/gas/elf/section20.d b/gas/testsuite/gas/elf/section20.d
new file mode 100644
index 0000000..cd7ab5e
--- /dev/null
+++ b/gas/testsuite/gas/elf/section20.d
@@ -0,0 +1,17 @@
+#readelf: -SWg
+#name: linked-to section 3
+
+#...
+ +\[ *[0-9]+\] +__patchable_function_entries +PROGBITS +[0-9a-f]+ +[0-9a-f]+ +0+[248] +00 +WALG +.*
+#...
+ +\[ *[0-9]+\] +__patchable_function_entries +PROGBITS +[0-9a-f]+ +[0-9a-f]+ +0+[248] +00 +WALG +.*
+#...
+COMDAT group section \[[ 0-9]+\] `.group' \[foo\] contains [0-9]+ sections:
+   \[Index\]    Name
+#...
+   \[[ 0-9]+\]   __patchable_function_entries
+#...
+COMDAT group section \[[ 0-9]+\] `.group' \[bar\] contains [0-9]+ sections:
+#...
+   \[[ 0-9]+\]   __patchable_function_entries
+#pass
diff --git a/gas/testsuite/gas/elf/section20.s b/gas/testsuite/gas/elf/section20.s
new file mode 100644
index 0000000..1e9639e
--- /dev/null
+++ b/gas/testsuite/gas/elf/section20.s
@@ -0,0 +1,13 @@
+	.section .text,"axG",%progbits,foo,comdat
+foo:
+	.section __patchable_function_entries,"awoG",%progbits,foo,foo,comdat
+	.dc.a	.LPFE1
+	.section .text,"axG",%progbits,foo,comdat
+.LPFE1:
+	.byte 0
+	.section __patchable_function_entries,"awoG",%progbits,bar,bar,comdat,unique,4
+	.dc.a	.LPFE2
+	.section .text,"axG",%progbits,bar,comdat,unique,24
+bar:
+.LPFE2:
+	.byte 0
diff --git a/gas/testsuite/gas/elf/section21.d b/gas/testsuite/gas/elf/section21.d
new file mode 100644
index 0000000..54fa9d4
--- /dev/null
+++ b/gas/testsuite/gas/elf/section21.d
@@ -0,0 +1,2 @@
+#name: incorrect linked-to symbols
+#error_output: section21.l
diff --git a/gas/testsuite/gas/elf/section21.l b/gas/testsuite/gas/elf/section21.l
new file mode 100644
index 0000000..50342ec
--- /dev/null
+++ b/gas/testsuite/gas/elf/section21.l
@@ -0,0 +1,5 @@
+[^:]*: Assembler messages:
+[^:]*:11: Error: junk at end of line, first unrecognized character is `1'
+#...
+[^:]*: 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/section21.s b/gas/testsuite/gas/elf/section21.s
new file mode 100644
index 0000000..ae5f848
--- /dev/null
+++ b/gas/testsuite/gas/elf/section21.s
@@ -0,0 +1,15 @@
+	.section __patchable_function_entries,"awo",%progbits,bar
+	.dc.a	.LPFE1
+	.text
+.LPFE1:
+	.byte 0
+	.section __patchable_function_entries,"awo",%progbits,foo
+	.dc.a	.LPFE2
+	.text
+.LPFE2:
+	.dc.a foo
+	.section __patchable_function_entries,"awo",%progbits,1foo
+	.dc.a	.LPFE3
+	.text
+.LPFE3:
+	.byte 0