[PATCH 2/4] aarch64: Fix incorrect sysreg notes operand notes

[Alice Carlotti]

When support for Armv8-R was added in 2020, aarch64_print_operand was
modified to check architecture features when searching for a system
register name.  However, this mismatch is then conflated with
read-only/write-only mismatches, leading to incorrect note emission when
reading a read-only or writing a write-only system register that is not
available in whichever of Armv8-A or Armv8-R we are using.

The original code also segfaults when parsing `msr mpuir_el1, w1'.  This
segfault arises while suggesting alternative assembler input with
corrected qualifiers, due to a missing NULL check when attempting to
emit notes.  The segfault is unreachable after this change, but a
subsequent patch will incorporate NULL checking anyway.

Once notes are enabled by default, an existing `mrs x0, mpuir_el1' test
will verify that the incorrect notes are no longer generated.


diff --git a/opcodes/aarch64-opc.c b/opcodes/aarch64-opc.c
index b074765920ed88f2d39c5fdf738a7c472db03eb3..d7e697e72479824f47c3c93f5b379851983683b5 100644
--- a/opcodes/aarch64-opc.c
+++ b/opcodes/aarch64-opc.c
@@ -5024,9 +5024,11 @@ aarch64_print_operand (char *buf, size_t size, bfd_vma pc,
 		 indicates what we didn't want for this instruction.  e.g. If
 		 F_REG_READ is there, that means we were looking for a write
 		 register.  See aarch64_ext_sysreg.  */
-	      if (aarch64_sys_regs[i].flags & F_REG_WRITE)
+	      if (aarch64_sys_regs[i].flags & F_REG_WRITE
+		  && !(opnd->sysreg.flags & F_REG_WRITE))
 		*notes = _("reading from a write-only register");
-	      else if (aarch64_sys_regs[i].flags & F_REG_READ)
+	      else if (aarch64_sys_regs[i].flags & F_REG_READ
+		       && !(opnd->sysreg.flags & F_REG_READ))
 		*notes = _("writing to a read-only register");
 	    }
 	}