[BFD, AArch64] Improve bti/pac plts.

This patch aims to improve the definitions of BTI and PAC based PLTs.
The following changes are made:
   * PLT0 does not need PAC instructions since the PLTGOT[2] (and PLTGOT[1])
     are readonly so they cannot be corrupted at runtime. Thus both PAC plt0
     and BTI+PAC plt0 are removed and we can use basic plt0 and BTI plt0
     instead, respectively.
   * We can remove the extra padding nops when we add the new bti instructions.
     BTI plt0 and BTI TLSDESC plt are updated.
   * For better performance PLTn could be padded to 24bytes. Both BTI pltn and
     PAC pltn are updated.

*** bfd/ChangeLog ***

2019-04-25  Sudakshina Das  <sudi.das@arm.com>

	* elfnn-aarch64.c (PLT_BTI_ENTRY_SIZE): Remove.
	(PLT_BTI_TLSDESC_ENTRY_SIZE): Remove.
	(PLT_PAC_ENTRY_SIZE, PLT_BTI_PAC_ENTRY_SIZE): Remove.
	(PLT_BTI_SMALL_ENTRY_SIZE, PLT_PAC_SMALL_ENTRY_SIZE): Update.
	(elfNN_aarch64_small_plt0_pac_entry): Remove.
	(elfNN_aarch64_small_plt0_bti_pac_entry): Remove.
	(elfNN_aarch64_small_plt0_bti_entry): Update.
	(elfNN_aarch64_small_plt_bti_entry): Update.
	(elfNN_aarch64_small_plt_pac_entry): Update.
	(elfNN_aarch64_tlsdesc_small_plt_bti_entry): Update.
	(setup_plt_values): Setup new entries.
	(elfNN_aarch64_finish_dynamic_sections): Remove size change.
	(elfNN_aarch64_plt_sym_val): Likewise.

*** ld/ChangeLog ***

2019-04-25  Sudakshina Das  <sudi.das@arm.com>

	* testsuite/ld-aarch64/bti-pac-plt-1.d: Update.
	* testsuite/ld-aarch64/bti-pac-plt-2.d: Update.
	* testsuite/ld-aarch64/bti-plt-1.d: Update.
	* testsuite/ld-aarch64/bti-plt-3.d: Update.
	* testsuite/ld-aarch64/bti-plt-5.d: Update.
	* testsuite/ld-aarch64/pac-plt-1.d: Update.
	* testsuite/ld-aarch64/pac-plt-2.d: Update.

1 files changed, 7 insertions, 60 deletions

diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index 9d4df11..8940f4e 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -268,14 +268,10 @@
 #define PLT_SMALL_ENTRY_SIZE		(16)
 #define PLT_TLSDESC_ENTRY_SIZE		(32)
 /* PLT sizes with BTI insn.  */
-#define PLT_BTI_ENTRY_SIZE		(36)
-#define PLT_BTI_SMALL_ENTRY_SIZE	(20)
-#define PLT_BTI_TLSDESC_ENTRY_SIZE	(36)
+#define PLT_BTI_SMALL_ENTRY_SIZE	(24)
 /* PLT sizes with PAC insn.  */
-#define PLT_PAC_ENTRY_SIZE		(36)
-#define PLT_PAC_SMALL_ENTRY_SIZE	(20)
+#define PLT_PAC_SMALL_ENTRY_SIZE	(24)
 /* PLT sizes with BTI and PAC insn.  */
-#define PLT_BTI_PAC_ENTRY_SIZE		(40)
 #define PLT_BTI_PAC_SMALL_ENTRY_SIZE	(24)
 
 /* Encoding of the nop instruction.  */
@@ -307,7 +303,7 @@ static const bfd_byte elfNN_aarch64_small_plt0_entry[PLT_ENTRY_SIZE] =
   0x1f, 0x20, 0x03, 0xd5,	/* nop */
 };
 
-static const bfd_byte elfNN_aarch64_small_plt0_bti_entry[PLT_BTI_ENTRY_SIZE] =
+static const bfd_byte elfNN_aarch64_small_plt0_bti_entry[PLT_ENTRY_SIZE] =
 {
   0x5f, 0x24, 0x03, 0xd5,	/* bti c.  */
   0xf0, 0x7b, 0xbf, 0xa9,	/* stp x16, x30, [sp, #-16]!  */
@@ -322,45 +318,6 @@ static const bfd_byte elfNN_aarch64_small_plt0_bti_entry[PLT_BTI_ENTRY_SIZE] =
   0x20, 0x02, 0x1f, 0xd6,	/* br x17  */
   0x1f, 0x20, 0x03, 0xd5,	/* nop */
   0x1f, 0x20, 0x03, 0xd5,	/* nop */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
-};
-
-static const bfd_byte elfNN_aarch64_small_plt0_pac_entry[PLT_PAC_ENTRY_SIZE] =
-{
-  0xf0, 0x7b, 0xbf, 0xa9,	/* stp x16, x30, [sp, #-16]!  */
-  0x10, 0x00, 0x00, 0x90,	/* adrp x16, (GOT+16)  */
-#if ARCH_SIZE == 64
-  0x11, 0x0A, 0x40, 0xf9,	/* ldr x17, [x16, #PLT_GOT+0x10]  */
-  0x10, 0x42, 0x00, 0x91,	/* add x16, x16,#PLT_GOT+0x10   */
-#else
-  0x11, 0x0A, 0x40, 0xb9,	/* ldr w17, [x16, #PLT_GOT+0x8]  */
-  0x10, 0x22, 0x00, 0x11,	/* add w16, w16,#PLT_GOT+0x8   */
-#endif
-  0x9f, 0x21, 0x03, 0xd5,	/* autia1716 */
-  0x20, 0x02, 0x1f, 0xd6,	/* br x17  */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
-};
-
-static const bfd_byte
-elfNN_aarch64_small_plt0_bti_pac_entry[PLT_BTI_PAC_ENTRY_SIZE] =
-{
-  0x5f, 0x24, 0x03, 0xd5,	/* bti c.  */
-  0xf0, 0x7b, 0xbf, 0xa9,	/* stp x16, x30, [sp, #-16]!  */
-  0x10, 0x00, 0x00, 0x90,	/* adrp x16, (GOT+16)  */
-#if ARCH_SIZE == 64
-  0x11, 0x0A, 0x40, 0xf9,	/* ldr x17, [x16, #PLT_GOT+0x10]  */
-  0x10, 0x42, 0x00, 0x91,	/* add x16, x16,#PLT_GOT+0x10   */
-#else
-  0x11, 0x0A, 0x40, 0xb9,	/* ldr w17, [x16, #PLT_GOT+0x8]  */
-  0x10, 0x22, 0x00, 0x11,	/* add w16, w16,#PLT_GOT+0x8   */
-#endif
-  0x9f, 0x21, 0x03, 0xd5,	/* autia1716 */
-  0x20, 0x02, 0x1f, 0xd6,	/* br x17  */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
 };
 
 /* Per function entry in a procedure linkage table looks like this
@@ -392,6 +349,7 @@ elfNN_aarch64_small_plt_bti_entry[PLT_BTI_SMALL_ENTRY_SIZE] =
   0x10, 0x02, 0x00, 0x11,	/* add w16, w16, :lo12:PLTGOT + n * 4  */
 #endif
   0x20, 0x02, 0x1f, 0xd6,	/* br x17.  */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
 };
 
 static const bfd_byte
@@ -407,6 +365,7 @@ elfNN_aarch64_small_plt_pac_entry[PLT_PAC_SMALL_ENTRY_SIZE] =
 #endif
   0x9f, 0x21, 0x03, 0xd5,	/* autia1716 */
   0x20, 0x02, 0x1f, 0xd6,	/* br x17.  */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
 };
 
 static const bfd_byte
@@ -444,7 +403,7 @@ elfNN_aarch64_tlsdesc_small_plt_entry[PLT_TLSDESC_ENTRY_SIZE] =
 };
 
 static const bfd_byte
-elfNN_aarch64_tlsdesc_small_plt_bti_entry[PLT_BTI_TLSDESC_ENTRY_SIZE] =
+elfNN_aarch64_tlsdesc_small_plt_bti_entry[PLT_TLSDESC_ENTRY_SIZE] =
 {
   0x5f, 0x24, 0x03, 0xd5,	/* bti c.  */
   0xe2, 0x0f, 0xbf, 0xa9,	/* stp x2, x3, [sp, #-16]! */
@@ -459,7 +418,6 @@ elfNN_aarch64_tlsdesc_small_plt_bti_entry[PLT_BTI_TLSDESC_ENTRY_SIZE] =
 #endif
   0x40, 0x00, 0x1f, 0xd6,	/* br x2 */
   0x1f, 0x20, 0x03, 0xd5,	/* nop */
-  0x1f, 0x20, 0x03, 0xd5,	/* nop */
 };
 
 #define elf_info_to_howto		elfNN_aarch64_info_to_howto
@@ -4758,9 +4716,7 @@ setup_plt_values (struct bfd_link_info *link_info,
 
   if (plt_type == PLT_BTI_PAC)
     {
-      globals->plt_header_size = PLT_BTI_PAC_ENTRY_SIZE;
-      globals->plt0_entry = elfNN_aarch64_small_plt0_bti_pac_entry;
-      globals->tlsdesc_plt_entry_size = PLT_BTI_TLSDESC_ENTRY_SIZE;
+      globals->plt0_entry = elfNN_aarch64_small_plt0_bti_entry;
 
       /* Only in ET_EXEC we need PLTn with BTI.  */
       if (bfd_link_pde (link_info))
@@ -4776,9 +4732,7 @@ setup_plt_values (struct bfd_link_info *link_info,
     }
   else if (plt_type == PLT_BTI)
     {
-      globals->plt_header_size = PLT_BTI_ENTRY_SIZE;
       globals->plt0_entry = elfNN_aarch64_small_plt0_bti_entry;
-      globals->tlsdesc_plt_entry_size = PLT_BTI_TLSDESC_ENTRY_SIZE;
 
       /* Only in ET_EXEC we need PLTn with BTI.  */
       if (bfd_link_pde (link_info))
@@ -4789,9 +4743,6 @@ setup_plt_values (struct bfd_link_info *link_info,
     }
   else if (plt_type == PLT_PAC)
     {
-      globals->plt_header_size = PLT_PAC_ENTRY_SIZE;
-      globals->plt0_entry = elfNN_aarch64_small_plt0_pac_entry;
-      globals->tlsdesc_plt_entry_size = PLT_TLSDESC_ENTRY_SIZE;
       globals->plt_entry_size = PLT_PAC_SMALL_ENTRY_SIZE;
       globals->plt_entry = elfNN_aarch64_small_plt_pac_entry;
     }
@@ -9720,7 +9671,6 @@ elfNN_aarch64_finish_dynamic_sections (bfd *output_bfd,
 	  if (type == PLT_BTI || type == PLT_BTI_PAC)
 	    {
 	      entry = elfNN_aarch64_tlsdesc_small_plt_bti_entry;
-	      htab->tlsdesc_plt_entry_size = PLT_BTI_TLSDESC_ENTRY_SIZE;
 	    }
 
 	  memcpy (htab->root.splt->contents + htab->tlsdesc_plt,
@@ -9896,7 +9846,6 @@ elfNN_aarch64_plt_sym_val (bfd_vma i, const asection *plt,
 
   if (elf_aarch64_tdata (plt->owner)->plt_type == PLT_BTI_PAC)
     {
-      plt0_size = PLT_BTI_PAC_ENTRY_SIZE;
       if (elf_elfheader (plt->owner)->e_type == ET_EXEC)
 	pltn_size = PLT_BTI_PAC_SMALL_ENTRY_SIZE;
       else
@@ -9904,13 +9853,11 @@ elfNN_aarch64_plt_sym_val (bfd_vma i, const asection *plt,
     }
   else if (elf_aarch64_tdata (plt->owner)->plt_type == PLT_BTI)
     {
-      plt0_size = PLT_BTI_ENTRY_SIZE;
       if (elf_elfheader (plt->owner)->e_type == ET_EXEC)
 	pltn_size = PLT_BTI_SMALL_ENTRY_SIZE;
     }
   else if (elf_aarch64_tdata (plt->owner)->plt_type == PLT_PAC)
     {
-      plt0_size = PLT_PAC_ENTRY_SIZE;
       pltn_size = PLT_PAC_SMALL_ENTRY_SIZE;
     }