[Morello] Capability support for exception headers

- Identify and mark C64 frames
- Identify C64 registers including DDC.
- Identify 'purecap' argument to .cfi_startproc for C64 frames
- Emit 'C' in augmentation string for C64 frames
- Recognise the 'C' in the CIE augmentation string when parsing
  exception headers

Difference from LLVM: The llvm assembler only uses purecap to add C to
the augmentation string.  The GNU assembler on the other hand uses
-march and validates that purecap is passed to .cfi_startproc only for
-morello+c64.  This means that for code compiled for A64, if llvm sees
`.cfi_startproc purecap`, it sets 'C' whereas the GNU assembler flags
an error.

bfd/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* elf-bfd.h (elf_backend_data): New callback
	elf_backend_eh_frame_augmentation_char.
	* elf-eh-frame.c (_bfd_elf_parse_eh_frame): Use it.
	* elfnn-aarch64.c (elf64_aarch64_eh_frame_augmentation_char):
	New function.
	(elf_backend_eh_frame_augmentation_char): New macro.

	* elfxx-target.h [!elf_backend_eh_frame_augmentation_char]:
	Set elf_backend_eh_frame_augmentation_char to NULL.
	(elfNN_bed): Initialise
	elf_backend_eh_frame_augmentation_char.

binutils/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* dwarf.c (dwarf_regnames_aarch64): Add capability registers.

gas/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* config/tc-aarch64.c (REG_DW_CSP, REG_DW_CLR): New macros.
	(s_aarch64_cfi_b_key_frame): Adjust for new entry_extras
	struct.
	(tc_aarch64_frame_initial_instructions): Adjust for C64.
	(tc_aarch64_fde_entry_init_extra,
	tc_aarch64_cfi_startproc_exp): New functions.
	(tc_aarch64_regname_to_dw2regnum): Support capability
	registers.
	* config/tc-aarch64.h (fde_entry): Forward declaration.
	(eh_entry_extras): New struct.
	(tc_fde_entry_extras, tc_cie_entry_extras): Use it.
	(tc_fde_entry_init_extra): Set to
	tc_aarch64_fde_entry_init_extra.
	(tc_output_cie_extra): Emit 'C' for C64.
	(tc_cie_fde_equivalent_extra): Adjust for C64.
	(tc_cie_entry_init_extra): Likewise.
	(tc_cfi_startproc_exp): New macro.
	(tc_aarch64_cfi_startproc_exp,
	tc_aarch64_fde_entry_init_extra): New function declarations.
	* dw2gencfi.c (tc_cfi_startproc_exp): New macro.
	(dot_cfi_startproc): Use it.
	* testsuite/gas/aarch64/morello-eh.d: New test.
	* testsuite/gas/aarch64/morello-eh.s: New test.

5 files changed, 41 insertions, 7 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 54abe00f310..e714ede5d33 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,5 +1,19 @@
 2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>
 
+	* elf-bfd.h (elf_backend_data): New callback
+	elf_backend_eh_frame_augmentation_char.
+	* elf-eh-frame.c (_bfd_elf_parse_eh_frame): Use it.
+	* elfnn-aarch64.c (elf64_aarch64_eh_frame_augmentation_char):
+	New function.
+	(elf_backend_eh_frame_augmentation_char): New macro.
+
+	* elfxx-target.h [!elf_backend_eh_frame_augmentation_char]:
+	Set elf_backend_eh_frame_augmentation_char to NULL.
+	(elfNN_bed): Initialise
+	elf_backend_eh_frame_augmentation_char.
+
+2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>
+
 	* elfnn-aarch64.c (STUB_ENTRY_NAME): Add format specifier for
 	veneer type.
 	(C64_MAX_ADRP_IMM, C64_MIN_ADRP_IMM): New macros.
diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index 98165af1335..f383cd8bf6e 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -1390,6 +1390,8 @@ struct elf_backend_data
      (bfd *, struct bfd_link_info *, asection *);
   bfd_boolean (*elf_backend_can_make_lsda_relative_eh_frame)
      (bfd *, struct bfd_link_info *, asection *);
+  bfd_boolean (*elf_backend_eh_frame_augmentation_char)
+    (char);
 
   /* This function returns an encoding after computing the encoded
      value (and storing it in ENCODED) for the given OFFSET into OSEC,
diff --git a/bfd/elf-eh-frame.c b/bfd/elf-eh-frame.c
index 7a129b00f8d..54da9bec11f 100644
--- a/bfd/elf-eh-frame.c
+++ b/bfd/elf-eh-frame.c
@@ -597,6 +597,7 @@ _bfd_elf_parse_eh_frame (bfd *abfd, struct bfd_link_info *info,
   unsigned int num_cies;
   unsigned int num_entries;
   elf_gc_mark_hook_fn gc_mark_hook;
+  const struct elf_backend_data *bed = get_elf_backend_data (abfd);
 
   htab = elf_hash_table (info);
   hdr_info = &htab->eh_info;
@@ -623,8 +624,7 @@ _bfd_elf_parse_eh_frame (bfd *abfd, struct bfd_link_info *info,
      it (it would need to use 64-bit .eh_frame format anyway).  */
   REQUIRE (sec->size == (unsigned int) sec->size);
 
-  ptr_size = (get_elf_backend_data (abfd)
-	      ->elf_backend_eh_frame_address_size (abfd, sec));
+  ptr_size = bed->elf_backend_eh_frame_address_size (abfd, sec);
   REQUIRE (ptr_size != 0);
 
   /* Go through the section contents and work out how many FDEs and
@@ -692,7 +692,7 @@ _bfd_elf_parse_eh_frame (bfd *abfd, struct bfd_link_info *info,
 
   buf = ehbuf;
   cie_count = 0;
-  gc_mark_hook = get_elf_backend_data (abfd)->gc_mark_hook;
+  gc_mark_hook = bed->gc_mark_hook;
   while ((bfd_size_type) (buf - ehbuf) != sec->size)
     {
       char *aug;
@@ -840,8 +840,12 @@ _bfd_elf_parse_eh_frame (bfd *abfd, struct bfd_link_info *info,
 		    }
 		    break;
 		  default:
-		    /* Unrecognized augmentation. Better bail out.  */
-		    goto free_no_table;
+		    /* Unrecognized augmentation. Better bail out if the target
+		       cannot recognised it.  */
+		    if (bed->elf_backend_eh_frame_augmentation_char == NULL
+			|| (!bed->elf_backend_eh_frame_augmentation_char
+			    (*(aug - 1))))
+		      goto free_no_table;
 		  }
 	    }
 	  this_inf->u.cie.aug_data_len
@@ -850,8 +854,7 @@ _bfd_elf_parse_eh_frame (bfd *abfd, struct bfd_link_info *info,
 	  /* For shared libraries, try to get rid of as many RELATIVE relocs
 	     as possible.  */
 	  if (bfd_link_pic (info)
-	      && (get_elf_backend_data (abfd)
-		  ->elf_backend_can_make_relative_eh_frame
+	      && (bed->elf_backend_can_make_relative_eh_frame
 		  (abfd, info, sec)))
 	    {
 	      if ((cie->fde_encoding & 0x70) == DW_EH_PE_absptr)
diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index bd7da1610a7..f1a43e18e0e 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -10934,6 +10934,14 @@ elfNN_aarch64_got_header_size (struct bfd_link_info *info)
   return GOT_ENTRY_SIZE (htab) * GOT_RESERVED_HEADER_SLOTS;
 }
 
+/* Identify the 'C' in the CIE augmentation string.  */
+
+static bfd_boolean
+elf64_aarch64_eh_frame_augmentation_char (const char aug)
+{
+  return aug == 'C';
+}
+
 /* We use this so we can override certain functions
    (though currently we don't).  */
 
@@ -11084,6 +11092,9 @@ const struct elf_size_info elfNN_aarch64_size_info =
 #define elf_backend_got_elt_size		\
   elfNN_aarch64_got_elt_size
 
+#define elf_backend_eh_frame_augmentation_char	\
+  elf64_aarch64_eh_frame_augmentation_char
+
 #define elf_backend_can_refcount       1
 #define elf_backend_can_gc_sections    1
 #define elf_backend_plt_readonly       1
diff --git a/bfd/elfxx-target.h b/bfd/elfxx-target.h
index d527a604f0f..ad8322e1596 100644
--- a/bfd/elfxx-target.h
+++ b/bfd/elfxx-target.h
@@ -654,6 +654,9 @@
 #ifndef elf_backend_can_make_lsda_relative_eh_frame
 #define elf_backend_can_make_lsda_relative_eh_frame	_bfd_elf_can_make_relative
 #endif
+#ifndef elf_backend_eh_frame_augmentation_char
+#define elf_backend_eh_frame_augmentation_char	NULL
+#endif
 #ifndef elf_backend_encode_eh_address
 #define elf_backend_encode_eh_address		_bfd_elf_encode_eh_address
 #endif
@@ -885,6 +888,7 @@ static struct elf_backend_data elfNN_bed =
   elf_backend_eh_frame_address_size,
   elf_backend_can_make_relative_eh_frame,
   elf_backend_can_make_lsda_relative_eh_frame,
+  elf_backend_eh_frame_augmentation_char,
   elf_backend_encode_eh_address,
   elf_backend_write_section,
   elf_backend_elfsym_local_is_section,