--gc-sections with groups and start/stop syms

The testcases added here show situations where synthesized start/stop
symbols don't cause their associated input sections to be marked.
Fixed with the elflink.c and ldlang.c changes.

bfd/
	PR 27500
	* elflink.c (_bfd_elf_gc_mark_rsec): Do special start/stop
	processing not when start/stop symbol section is unmarked but
	on first time a start/stop symbol is processed.
ld/
	* ldlang.c (insert_undefined): Don't mark symbols here.
	(lang_mark_undefineds): Do so here instead, new function.
	(lang_process): Call lang_mark_undefineds.
	* testsuite/ld-gc/start3.d,
	* testsuite/ld-gc/start3.s: New test.
	* testsuite/ld-gc/start4.d,
	* testsuite/ld-gc/start4.s: New test.
	* testsuite/ld-gc/gc.exp: Run them.

bfd/ChangeLog

@@ -1,3 +1,10 @@
+2021-03-03  Alan Modra  <amodra@gmail.com>
+
+	PR 27500
+	* elflink.c (_bfd_elf_gc_mark_rsec): Do special start/stop
+	processing not when start/stop symbol section is unmarked but
+	on first time a start/stop symbol is processed.
+
 2021-03-03  Alan Modra  <amodra@gmail.com>
 
 	* reloc.c: Include x86_64.h rather than internal.h.

bfd/elflink.c

@@ -13422,6 +13422,8 @@ _bfd_elf_gc_mark_rsec (struct bfd_link_info *info, asection *sec,
   if (r_symndx >= cookie->locsymcount
       || ELF_ST_BIND (cookie->locsyms[r_symndx].st_info) != STB_LOCAL)
     {
+      bfd_boolean was_marked;
+
       h = cookie->sym_hashes[r_symndx - cookie->extsymoff];
       if (h == NULL)
 	{
@@ -13432,6 +13434,8 @@ _bfd_elf_gc_mark_rsec (struct bfd_link_info *info, asection *sec,
       while (h->root.type == bfd_link_hash_indirect
 	     || h->root.type == bfd_link_hash_warning)
 	h = (struct elf_link_hash_entry *) h->root.u.i.link;
+
+      was_marked = h->mark;
       h->mark = 1;
       /* Keep all aliases of the symbol too.  If an object symbol
 	 needs to be copied into .dynbss then all of its aliases
@@ -13444,7 +13448,7 @@ _bfd_elf_gc_mark_rsec (struct bfd_link_info *info, asection *sec,
 	  hw->mark = 1;
 	}
 
-      if (h->start_stop && !h->root.ldscript_def)
+      if (!was_marked && h->start_stop && !h->root.ldscript_def)
 	{
 	  if (info->start_stop_gc)
 	    return NULL;
@@ -13455,7 +13459,7 @@ _bfd_elf_gc_mark_rsec (struct bfd_link_info *info, asection *sec,
 	  else if (start_stop != NULL)
 	    {
 	      asection *s = h->u2.start_stop_section;
-	      *start_stop = !s->gc_mark;
+	      *start_stop = TRUE;
 	      return s;
 	    }
 	}

ld/ChangeLog

@@ -1,3 +1,15 @@
+2021-03-03  Alan Modra  <amodra@gmail.com>
+
+	PR 27500
+	* ldlang.c (insert_undefined): Don't mark symbols here.
+	(lang_mark_undefineds): Do so here instead, new function.
+	(lang_process): Call lang_mark_undefineds.
+	* testsuite/ld-gc/start3.d,
+	* testsuite/ld-gc/start3.s: New test.
+	* testsuite/ld-gc/start4.d,
+	* testsuite/ld-gc/start4.s: New test.
+	* testsuite/ld-gc/gc.exp: Run them.
+
 2021-03-03  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-gc/gc.exp: Define UNDERSCORE in ASFLAGS.

ld/ldlang.c

@@ -3986,8 +3986,6 @@ insert_undefined (const char *name)
       h->type = bfd_link_hash_undefined;
       h->u.undef.abfd = NULL;
       h->non_ir_ref_regular = TRUE;
-      if (is_elf_hash_table (link_info.hash))
-	((struct elf_link_hash_entry *) h)->mark = 1;
       bfd_link_add_undef (link_info.hash, h);
     }
 }
@@ -4005,6 +4003,23 @@ lang_place_undefineds (void)
     insert_undefined (ptr->name);
 }
 
+/* Mark -u symbols against garbage collection.  */
+
+static void
+lang_mark_undefineds (void)
+{
+  ldlang_undef_chain_list_type *ptr;
+
+  if (bfd_get_flavour (link_info.output_bfd) == bfd_target_elf_flavour)
+    for (ptr = ldlang_undef_chain_list_head; ptr != NULL; ptr = ptr->next)
+      {
+	struct elf_link_hash_entry *h = (struct elf_link_hash_entry *)
+	  bfd_link_hash_lookup (link_info.hash, ptr->name, FALSE, FALSE, TRUE);
+	if (h != NULL)
+	  h->mark = 1;
+      }
+}
+
 /* Structure used to build the list of symbols that the user has required
    be defined.  */
 
@@ -8116,6 +8131,8 @@ lang_process (void)
   /* Remove unreferenced sections if asked to.  */
   lang_gc_sections ();
 
+  lang_mark_undefineds ();
+
   /* Check relocations.  */
   lang_check_relocs ();
 

ld/testsuite/ld-gc/gc.exp

@@ -101,6 +101,8 @@ if { [is_elf_format] } then {
     run_dump_test "stop"
     run_dump_test "start"
     run_dump_test "start2"
+    run_dump_test "start3"
+    run_dump_test "start4"
 }
 
 if { [is_elf_format] && [check_shared_lib_support] } then {

ld/testsuite/ld-gc/start3.d

@@ -0,0 +1,9 @@
+#name: --gc-sections with groups and start/stop syms
+#ld: --gc-sections -e _start
+#nm: -n
+#notarget: [is_generic]
+#xfail: bfin-*-*linux* frv-*-*linux* lm32-*-*linux*
+
+#...
+[0-9a-f]+ T +bar
+#...

ld/testsuite/ld-gc/start3.s

@@ -0,0 +1,29 @@
+	.text
+	.global _start
+_start:
+	.dc.a foo
+ .ifdef UNDERSCORE
+	.dc.a ___start_xx, ___stop_xx
+ .else
+	.dc.a __start_xx, __stop_xx
+ .endif
+
+	.section .text,"axG",%progbits,foo_group
+	.global foo
+foo:
+	.dc.a 0
+
+	.section xx,"aG",%progbits,foo_group
+	.global foo_xx
+foo_xx:
+	.dc.a 1
+
+	.section .text,"axG",%progbits,bar_group
+	.global bar
+bar:
+	.dc.a 2
+
+	.section xx,"aG",%progbits,bar_group
+	.global bar_xx
+bar_xx:
+	.dc.a 3

ld/testsuite/ld-gc/start4.d

@@ -0,0 +1,9 @@
+#name: --gc-sections with other syms and start/stop syms
+#ld: --gc-sections -e _start
+#nm: -n
+#target: [supports_gnu_unique]
+#xfail: bfin-*-*linux* frv-*-*linux* lm32-*-*linux*
+
+#...
+[0-9a-f]+ R +bar_xx
+#...

ld/testsuite/ld-gc/start4.s

@@ -0,0 +1,19 @@
+	.text
+	.global _start
+_start:
+	.dc.a foo_xx
+ .ifdef UNDERSCORE
+	.dc.a ___start_xx, ___stop_xx
+ .else
+	.dc.a __start_xx, __stop_xx
+ .endif
+
+	.section xx,"a",%progbits,unique,0
+	.global foo_xx
+foo_xx:
+	.dc.a 1
+
+	.section xx,"a",%progbits,unique,1
+	.global bar_xx
+bar_xx:
+	.dc.a 3