non-PIC references to __ehdr_start in pie and shared

Rather than hacking every backend to not discard dynamic relocations
against an undefined hidden __ehdr_start, make it appear to be defined
early.  We want __ehdr_start hidden before size_dynamic_sections so
that it isn't put in .dynsym, but we do need the dynamic relocations
for a PIE or shared library with a non-PIC reference.  Defining it
early is wrong if we don't actually define the symbol later to its
proper value.  (In some cases we want to leave the symbol undefined,
for example, when the ELF header isn't loaded, and we don't have this
infomation available in before_allocation.)

ld/
	* emultempl/elf32.em (gld${EMULATION_NAME}_before_allocation): Define
	__ehdr_start before size_dynamic_sections and restore afterwards.
ld/testsuite/
	* ld-elf/ehdr_start-shared.d: New.
	* ld-elf/ehdr_start-userdef.d: xfail frv.
	* ld-elf/ehdr_start-weak.d: Likewise.
	* ld-elf/ehdr_start.d: Likewise.

7 files changed, 44 insertions, 0 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index 2b7a573..eaa6b93 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,8 @@
+2014-01-15  Alan Modra  <amodra@gmail.com>
+
+	* emultempl/elf32.em (gld${EMULATION_NAME}_before_allocation): Define
+	__ehdr_start before size_dynamic_sections and restore afterwards.
+
 2014-01-10  Alan Modra  <amodra@gmail.com>
 
 	PR ld/14207
diff --git a/ld/emultempl/elf32.em b/ld/emultempl/elf32.em
index 9a2fe89..13f86f0 100644
--- a/ld/emultempl/elf32.em
+++ b/ld/emultempl/elf32.em
@@ -1480,6 +1480,8 @@ gld${EMULATION_NAME}_before_allocation (void)
   const char *rpath;
   asection *sinterp;
   bfd *abfd;
+  struct elf_link_hash_entry *ehdr_start = NULL;
+  struct bfd_link_hash_entry ehdr_start_save;
 
   if (is_elf_hash_table (link_info.hash))
     {
@@ -1504,6 +1506,16 @@ gld${EMULATION_NAME}_before_allocation (void)
              _bfd_elf_link_hash_hide_symbol (&link_info, h, TRUE);
              if (ELF_ST_VISIBILITY (h->other) != STV_INTERNAL)
                h->other = (h->other & ~ELF_ST_VISIBILITY (-1)) | STV_HIDDEN;
+	     /* Don't leave the symbol undefined.  Undefined hidden
+		symbols typically won't have dynamic relocations, but
+		we most likely will need dynamic relocations for
+		__ehdr_start if we are building a PIE or shared
+		library.  */
+	     ehdr_start = h;
+	     ehdr_start_save = h->root;
+	     h->root.type = bfd_link_hash_defined;
+	     h->root.u.def.section = bfd_abs_section_ptr;
+	     h->root.u.def.value = 0;
            }
        }
 
@@ -1620,6 +1632,14 @@ ${ELF_INTERPRETER_SET_DEFAULT}
 
   if (!bfd_elf_size_dynsym_hash_dynstr (link_info.output_bfd, &link_info))
     einfo ("%P%F: failed to set dynamic section sizes: %E\n");
+
+  if (ehdr_start != NULL)
+    {
+      /* If we twiddled __ehdr_start to defined earlier, put it back
+	 as it was.  */
+      ehdr_start->root.type = ehdr_start_save.type;
+      ehdr_start->root.u = ehdr_start_save.u;
+    }
 }
 
 EOF
diff --git a/ld/testsuite/ChangeLog b/ld/testsuite/ChangeLog
index cd97fd5..8fbd375 100644
--- a/ld/testsuite/ChangeLog
+++ b/ld/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2014-01-15  Alan Modra  <amodra@gmail.com>
+
+	* ld-elf/ehdr_start-shared.d: New.
+	* ld-elf/ehdr_start-userdef.d: xfail frv.
+	* ld-elf/ehdr_start-weak.d: Likewise.
+	* ld-elf/ehdr_start.d: Likewise.
+
 2014-01-14  Vidya Praveen  <vidyapraveen@arm.com>
 
 	* lib/ld-lib.exp (default_ld_link): Remove support for ldflags.
diff --git a/ld/testsuite/ld-elf/ehdr_start-shared.d b/ld/testsuite/ld-elf/ehdr_start-shared.d
new file mode 100644
index 0000000..c17516a
--- /dev/null
+++ b/ld/testsuite/ld-elf/ehdr_start-shared.d
@@ -0,0 +1,9 @@
+#source: ehdr_start.s
+#ld: -e _start -shared
+#nm: -n
+#target: *-*-linux* *-*-gnu* *-*-nacl*
+#xfail: cris*-*-* frv-*-*
+
+#...
+[0-9a-f]*000 [Adrt] __ehdr_start
+#pass
diff --git a/ld/testsuite/ld-elf/ehdr_start-userdef.d b/ld/testsuite/ld-elf/ehdr_start-userdef.d
index 2a88e98..b58ae3f 100644
--- a/ld/testsuite/ld-elf/ehdr_start-userdef.d
+++ b/ld/testsuite/ld-elf/ehdr_start-userdef.d
@@ -2,6 +2,7 @@
 #ld: -e _start -T ehdr_start-userdef.t
 #readelf: -Ws
 #target: *-*-linux* *-*-gnu* *-*-nacl*
+#xfail: frv-*-*
 
 #...
 Symbol table '\.symtab' contains [0-9]+ entries:
diff --git a/ld/testsuite/ld-elf/ehdr_start-weak.d b/ld/testsuite/ld-elf/ehdr_start-weak.d
index 8bd9035..24ae34c 100644
--- a/ld/testsuite/ld-elf/ehdr_start-weak.d
+++ b/ld/testsuite/ld-elf/ehdr_start-weak.d
@@ -2,6 +2,7 @@
 #ld: -e _start -T ehdr_start-missing.t
 #nm: -n
 #target: *-*-linux* *-*-gnu* *-*-nacl*
+#xfail: frv-*-*
 
 #...
 \s+[wU] __ehdr_start
diff --git a/ld/testsuite/ld-elf/ehdr_start.d b/ld/testsuite/ld-elf/ehdr_start.d
index 52e5b54..d538b66 100644
--- a/ld/testsuite/ld-elf/ehdr_start.d
+++ b/ld/testsuite/ld-elf/ehdr_start.d
@@ -2,6 +2,7 @@
 #ld: -e _start
 #nm: -n
 #target: *-*-linux* *-*-gnu* *-*-nacl*
+#xfail: frv-*-*
 
 #...
 [0-9a-f]*000 [Adrt] __ehdr_start