aarch64/sme2: Teach binutils/BFD about the NT_ARM_ZT register set

The Scalable Matrix Extension v2 (SME2) defines a new register, ZT0, that
the Linux Kernel handles through a new NT_ARM_ZT register set.

Teach binutils/BFD about it so that gdb can make use of it for reading
and writing core files.  This also enables readelf/objdump to show the
correct identification for the NT_ARM_ZT register set.

Validated under Fast Models.

bfd/elf-bfd.h

@@ -2944,6 +2944,8 @@ extern char *elfcore_write_aarch_ssve
   (bfd *, char *, int *, const void *, int);
 extern char *elfcore_write_aarch_za
   (bfd *, char *, int *, const void *, int);
+extern char *elfcore_write_aarch_zt
+  (bfd *, char *, int *, const void *, int);
 extern char *elfcore_write_arc_v2
   (bfd *, char *, int *, const void *, int);
 extern char *elfcore_write_riscv_csr

bfd/elf.c

@@ -10691,6 +10691,15 @@ elfcore_grok_aarch_za (bfd *abfd, Elf_Internal_Note *note)
   return elfcore_make_note_pseudosection (abfd, ".reg-aarch-za", note);
 }
 
+/* Convert NOTE into a bfd_section called ".reg-aarch-zt".  Return TRUE if
+   successful, otherwise return FALSE.  */
+
+static bool
+elfcore_grok_aarch_zt (bfd *abfd, Elf_Internal_Note *note)
+{
+  return elfcore_make_note_pseudosection (abfd, ".reg-aarch-zt", note);
+}
+
 static bool
 elfcore_grok_arc_v2 (bfd *abfd, Elf_Internal_Note *note)
 {
@@ -11420,6 +11429,13 @@ elfcore_grok_note (bfd *abfd, Elf_Internal_Note *note)
       else
 	return true;
 
+    case NT_ARM_ZT:
+      if (note->namesz == 6
+	  && strcmp (note->namedata, "LINUX") == 0)
+	return elfcore_grok_aarch_zt (abfd, note);
+      else
+	return true;
+
     case NT_GDB_TDESC:
       if (note->namesz == 4
 	  && strcmp (note->namedata, "GDB") == 0)
@@ -13062,6 +13078,25 @@ elfcore_write_aarch_za (bfd *abfd,
 			     size);
 }
 
+/* Write the buffer of zt register values in aarch_zt (length SIZE) into
+   the note buffer BUF and update *BUFSIZ.  ABFD is the bfd the note is being
+   written into.  Return a pointer to the new start of the note buffer, to
+   replace BUF which may no longer be valid.  */
+
+char *
+elfcore_write_aarch_zt (bfd *abfd,
+			char *buf,
+			int *bufsiz,
+			const void *aarch_zt,
+			int size)
+{
+  char *note_name = "LINUX";
+  return elfcore_write_note (abfd, buf, bufsiz,
+			     note_name, NT_ARM_ZT,
+			     aarch_zt,
+			     size);
+}
+
 char *
 elfcore_write_arc_v2 (bfd *abfd,
 		      char *buf,
@@ -13247,6 +13282,8 @@ elfcore_write_register_note (bfd *abfd,
     return elfcore_write_aarch_ssve (abfd, buf, bufsiz, data, size);
   if (strcmp (section, ".reg-aarch-za") == 0)
     return elfcore_write_aarch_za (abfd, buf, bufsiz, data, size);
+  if (strcmp (section, ".reg-aarch-zt") == 0)
+    return elfcore_write_aarch_zt (abfd, buf, bufsiz, data, size);
   if (strcmp (section, ".reg-arc-v2") == 0)
     return elfcore_write_arc_v2 (abfd, buf, bufsiz, data, size);
   if (strcmp (section, ".gdb-tdesc") == 0)

binutils/readelf.c

@@ -20039,6 +20039,8 @@ get_note_type (Filedata * filedata, unsigned e_type)
 	return _("NT_ARM_SSVE (AArch64 streaming SVE registers)");
       case NT_ARM_ZA:
 	return _("NT_ARM_ZA (AArch64 SME ZA register)");
+      case NT_ARM_ZT:
+	return _("NT_ARM_ZT (AArch64 SME2 ZT registers)");
       case NT_ARM_PAC_ENABLED_KEYS:
 	return _("NT_ARM_PAC_ENABLED_KEYS (AArch64 pointer authentication enabled keys)");
       case NT_ARC_V2:

include/elf/common.h

@@ -701,6 +701,8 @@
 					/*   Note: name must be "LINUX".  */
 #define NT_ARM_ZA       0x40c           /* AArch64 SME ZA register.  */
 					/*   Note: name must be "LINUX".  */
+#define NT_ARM_ZT       0x40d           /* AArch64 SME2 ZT registers.  */
+					/*   Note: name must be "LINUX".  */
 #define NT_ARC_V2	0x600		/* ARC HS accumulator/extra registers.  */
 					/*   note name must be "LINUX".  */
 #define NT_LARCH_CPUCFG 0xa00		/* LoongArch CPU config registers */