--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.

7 files changed, 99 insertions, 2 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index bf1d226..0f1da7f 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,5 +1,17 @@
 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.
 	Move tests with ELF section directives to is_elf_format block.
 	* testsuite/ld-gc/abi-note.d: Run on more targets.
diff --git a/ld/ldlang.c b/ld/ldlang.c
index a77e8fa..684e1d2 100644
--- a/ld/ldlang.c
+++ b/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 ();
 
diff --git a/ld/testsuite/ld-gc/gc.exp b/ld/testsuite/ld-gc/gc.exp
index ba528d0..cd5c6f7 100644
--- a/ld/testsuite/ld-gc/gc.exp
+++ b/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 {
diff --git a/ld/testsuite/ld-gc/start3.d b/ld/testsuite/ld-gc/start3.d
new file mode 100644
index 0000000..a57dab1
--- /dev/null
+++ b/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
+#...
diff --git a/ld/testsuite/ld-gc/start3.s b/ld/testsuite/ld-gc/start3.s
new file mode 100644
index 0000000..0e720ba
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-gc/start4.d b/ld/testsuite/ld-gc/start4.d
new file mode 100644
index 0000000..ae77aa9
--- /dev/null
+++ b/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
+#...
diff --git a/ld/testsuite/ld-gc/start4.s b/ld/testsuite/ld-gc/start4.s
new file mode 100644
index 0000000..1aa9445
--- /dev/null
+++ b/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