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.

10 files changed, 98 insertions, 0 deletions

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