elf: Strip zero-sized dynamic sections

ELF size_dynamic_sections is called by the ELF backend linker after all
the linker input files have been seen but before the section sizes have
been set.  After the sections sizes have been set, target-specific,
global optimizations may make some dynamic sections zero-sized if they
are no longer needed.

Add ELF strip_zero_sized_dynamic_sections so that ELF backend linker can
strip zero-sized dynamic sections after the sections sizes have been set.

bfd/

	PR ld/25849
	* elf-bfd.h (elf_backend_data): Add
	elf_backend_strip_zero_sized_dynamic_sections.
	(_bfd_elf_strip_zero_sized_dynamic_sections): New prototype.
	* elf64-alpha.c (elf_backend_strip_zero_sized_dynamic_sections):
	New macro.
	* elflink.c (_bfd_elf_strip_zero_sized_dynamic_sections): New
	function.
	* elfxx-target.h (elf_backend_strip_zero_sized_dynamic_sections):
	New macro.
	(elfNN_bed): Add elf_backend_strip_zero_sized_dynamic_sections.

ld/

	PR ld/25849
	* ldelfgen.c (ldelf_map_segments): Call
	elf_backend_strip_zero_sized_dynamic_sections.
	* testsuite/ld-alpha/tlsbinr.rd: Updated.

3 files changed, 67 insertions, 52 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index dffd363..1169f93 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,10 @@
+2020-04-21  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/25849
+	* ldelfgen.c (ldelf_map_segments): Call
+	elf_backend_strip_zero_sized_dynamic_sections.
+	* testsuite/ld-alpha/tlsbinr.rd: Updated.
+
 2020-04-20  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-powerpc/tlsopt5.s: Rename foo to aaaaa.
diff --git a/ld/ldelfgen.c b/ld/ldelfgen.c
index 21739b1..c0568f1 100644
--- a/ld/ldelfgen.c
+++ b/ld/ldelfgen.c
@@ -73,6 +73,19 @@ ldelf_map_segments (bfd_boolean need_layout)
 
   if (tries == 0)
     einfo (_("%F%P: looping in map_segments"));
+
+  if (link_info.output_bfd->xvec->flavour == bfd_target_elf_flavour
+      && lang_phdr_list == NULL)
+    {
+      /* If we don't have user supplied phdrs, strip zero-sized dynamic
+	 sections and regenerate program headers.  */
+      const struct elf_backend_data *bed
+	= get_elf_backend_data (link_info.output_bfd);
+      if (bed->elf_backend_strip_zero_sized_dynamic_sections
+	  && !bed->elf_backend_strip_zero_sized_dynamic_sections
+		(&link_info))
+	  einfo (_("%F%P: failed to strip zero-sized dynamic sections"));
+    }
 }
 
 /* We want to emit CTF early if and only if we are not targetting ELF with this
diff --git a/ld/testsuite/ld-alpha/tlsbinr.rd b/ld/testsuite/ld-alpha/tlsbinr.rd
index d6a70f9..ea51686 100644
--- a/ld/testsuite/ld-alpha/tlsbinr.rd
+++ b/ld/testsuite/ld-alpha/tlsbinr.rd
@@ -16,8 +16,6 @@ Section Headers:
  +\[[ 0-9]+\] \.dynsym +.*
  +\[[ 0-9]+\] \.dynstr +.*
  +\[[ 0-9]+\] \.rela\.dyn +.*
- +\[[ 0-9]+\] \.rela\.plt +.*
- +\[[ 0-9]+\] \.plt +PROGBITS +[0-9a-f]+ [0-9a-f]+ [0-9a-f]+ 0+ +AX +0 +0 +16
  +\[[ 0-9]+\] \.text +PROGBITS +[0-9a-f]+ [0-9a-f]+ [0-9a-f]+ 0+ +AX +0 +0 4096
  +\[[ 0-9]+\] \.eh_frame +PROGBITS +[0-9a-f]+ [0-9a-f]+ [0-9a-f]+ 00 +A +0 +0 +8
  +\[[ 0-9]+\] \.tdata +PROGBITS +[0-9a-f]+ [0-9a-f]+ [0-9a-f]+ 0+ WAT +0 +0 +4
@@ -70,59 +68,56 @@ Symbol table '\.symtab' contains [0-9]+ entries:
 [0-9 ]+: [0-9a-f]+ +0 +SECTION +LOCAL +DEFAULT +9 
 [0-9 ]+: [0-9a-f]+ +0 +SECTION +LOCAL +DEFAULT +10 
 [0-9 ]+: [0-9a-f]+ +0 +SECTION +LOCAL +DEFAULT +11 
-[0-9 ]+: [0-9a-f]+ +0 +SECTION +LOCAL +DEFAULT +12 
-[0-9 ]+: [0-9a-f]+ +0 +SECTION +LOCAL +DEFAULT +13 
 .* FILE +LOCAL +DEFAULT +ABS .*
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl1
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl2
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl3
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl4
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl5
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl6
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl7
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +10 sl8
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl1
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl2
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl3
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl4
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl5
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl6
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl7
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +8 sl8
 .* FILE +LOCAL +DEFAULT +ABS .*
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl1
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl2
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl3
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl4
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl5
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl6
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl7
-[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +11 bl8
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl1
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl2
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl3
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl4
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl5
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl6
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl7
+[0-9 ]+: [0-9a-f]+ +0 +TLS +LOCAL +DEFAULT +9 bl8
 .* FILE +LOCAL +DEFAULT +ABS .*
-[0-9 ]+: [0-9a-f]+ +0 +OBJECT +LOCAL +DEFAULT +12 _DYNAMIC
-[0-9 ]+: [0-9a-f]+ +0 +OBJECT +LOCAL +DEFAULT +7 _PROCEDURE_LINKAGE_TABLE_
-[0-9 ]+: [0-9a-f]+ +0 +OBJECT +LOCAL +DEFAULT +13 _GLOBAL_OFFSET_TABLE_
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg8
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg8
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg6
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg3
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg3
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh3
+[0-9 ]+: [0-9a-f]+ +0 +OBJECT +LOCAL +DEFAULT +10 _DYNAMIC
+[0-9 ]+: [0-9a-f]+ +0 +OBJECT +LOCAL +DEFAULT +11 _GLOBAL_OFFSET_TABLE_
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg8
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg8
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg6
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg3
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg3
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh3
 [0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +UND sG2
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg4
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg5
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg5
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg4
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg5
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg5
 [0-9 ]+: [0-9a-f]+ +0 +FUNC +GLOBAL +DEFAULT +UND __tls_get_addr
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh7
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh8
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg1
-[0-9 ]+: [0-9a-f]+ +52 +FUNC +GLOBAL +DEFAULT +8 _start
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh4
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg7
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh5
-[0-9 ]+: [0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +13 __bss_start
-[0-9 ]+: [0-9a-f]+ +136 +FUNC +GLOBAL +DEFAULT +\[STD GPLOAD\] +8 fn2
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg2
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh7
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh8
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg1
+[0-9 ]+: [0-9a-f]+ +52 +FUNC +GLOBAL +DEFAULT +6 _start
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh4
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg7
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh5
+[0-9 ]+: [0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +11 __bss_start
+[0-9 ]+: [0-9a-f]+ +136 +FUNC +GLOBAL +DEFAULT +\[STD GPLOAD\] +6 fn2
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg2
 [0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +UND sG1
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh1
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg6
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +10 sg7
-[0-9 ]+: [0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +13 _edata
-[0-9 ]+: [0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +13 _end
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh2
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +10 sh6
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg2
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg1
-[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +11 bg4
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh1
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg6
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +8 sg7
+[0-9 ]+: [0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +11 _edata
+[0-9 ]+: [0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +11 _end
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh2
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +HIDDEN +8 sh6
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg2
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg1
+[0-9 ]+: [0-9a-f]+ +0 +TLS +GLOBAL +DEFAULT +9 bg4