From: Alice Carlotti <alice.carlotti@arm.com>
Date: Wed, 5 Nov 2025 12:06:14 +0000 (+0000)
Subject: aarch64: Refactor sysreg operand printing
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1c5382e56d7c91b075f093e77d16b44c899dbfab;p=thirdparty%2Fbinutils-gdb.git

aarch64: Refactor sysreg operand printing

This hopefully makes the logic clearer.  It also adds NULL checks before
recording notes, and explicitly compares the inexactness of inexact
matches (although this extra comparison isn't used for any existing
encodings).
---

diff --git a/opcodes/aarch64-opc.c b/opcodes/aarch64-opc.c
index d7e697e7247..c501b9b35e5 100644
--- a/opcodes/aarch64-opc.c
+++ b/opcodes/aarch64-opc.c
@@ -4996,56 +4996,62 @@ aarch64_print_operand (char *buf, size_t size, bfd_vma pc,
 
     case AARCH64_OPND_SYSREG:
     case AARCH64_OPND_SYSREG128:
-      for (i = 0; aarch64_sys_regs[i].name; ++i)
-	{
-	  const aarch64_sys_reg *sr = aarch64_sys_regs + i;
-
-	  bool exact_match
-	    = (!(sr->flags & (F_REG_READ | F_REG_WRITE))
-	    || (sr->flags & opnd->sysreg.flags) == opnd->sysreg.flags)
-	    && AARCH64_CPU_HAS_ALL_FEATURES (features, sr->features);
-
-	  /* Try and find an exact match, But if that fails, return the first
-	     partial match that was found.  */
-	  if (aarch64_sys_regs[i].value == opnd->sysreg.value
-	      && ! aarch64_sys_reg_deprecated_p (aarch64_sys_regs[i].flags)
-	      && ! aarch64_sys_reg_alias_p (aarch64_sys_regs[i].flags)
-	      && (name == NULL || exact_match))
-	    {
-	      name = aarch64_sys_regs[i].name;
-	      if (exact_match)
-		{
-		  if (notes)
-		    *notes = NULL;
-		  break;
-		}
+      {
+	int min_mismatch = 999;
+	int best_index = -1;
+	uint32_t op_flags = opnd->sysreg.flags;
+	for (i = 0; aarch64_sys_regs[i].name; ++i)
+	  {
+	    const aarch64_sys_reg *sr = aarch64_sys_regs + i;
 
-	      /* If we didn't match exactly, that means the presense of a flag
-		 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
-		  && !(opnd->sysreg.flags & F_REG_WRITE))
-		*notes = _("reading from a write-only register");
-	      else if (aarch64_sys_regs[i].flags & F_REG_READ
-		       && !(opnd->sysreg.flags & F_REG_READ))
-		*notes = _("writing to a read-only register");
-	    }
-	}
+	    if (!(aarch64_sys_regs[i].value == opnd->sysreg.value)
+		|| aarch64_sys_reg_deprecated_p (aarch64_sys_regs[i].flags)
+		| aarch64_sys_reg_alias_p (aarch64_sys_regs[i].flags))
+	      continue;
 
-      if (name)
-	snprintf (buf, size, "%s", style_reg (styler, name));
-      else
-	{
-	  /* Implementation defined system register.  */
-	  unsigned int value = opnd->sysreg.value;
-	  snprintf (buf, size, "%s",
-		    style_reg (styler, "s%u_%u_c%u_c%u_%u",
-			       (value >> 14) & 0x3, (value >> 11) & 0x7,
-			       (value >> 7) & 0xf, (value >> 3) & 0xf,
-			       value & 0x7));
-	}
-      break;
+	    int mismatch_score = 0;
+	    if (!AARCH64_CPU_HAS_ALL_FEATURES (features, sr->features))
+	      mismatch_score += 1;
+	    /* This read/write check only works during disassembly.  During
+	       assembly the value of op_flags was copied from sr->flags.  */
+	    if (((sr->flags & F_REG_READ) && (op_flags & F_REG_WRITE))
+		|| ((sr->flags & F_REG_WRITE) && (op_flags & F_REG_READ)))
+	      mismatch_score += 2;
+
+	    if (mismatch_score < min_mismatch)
+	      {
+		min_mismatch = mismatch_score;
+		best_index = i;
+		if (mismatch_score == 0)
+		  break;
+	      }
+	  }
+	if (best_index == -1)
+	  {
+	    /* Use encoding-based name for unrecognised system register.  */
+	    unsigned int value = opnd->sysreg.value;
+	    snprintf (buf, size, "%s",
+		      style_reg (styler, "s%u_%u_c%u_c%u_%u",
+				 (value >> 14) & 0x3, (value >> 11) & 0x7,
+				 (value >> 7) & 0xf, (value >> 3) & 0xf,
+				 value & 0x7));
+	  }
+	else
+	  {
+	    const aarch64_sys_reg *sr = aarch64_sys_regs + best_index;
+	    snprintf (buf, size, "%s", style_reg (styler, sr->name));
+
+	    /* Add a note if we violated read/write constraints.  */
+	    if (notes && min_mismatch)
+	      {
+		if ((sr->flags & F_REG_READ) && (op_flags & F_REG_WRITE))
+		  *notes = _("writing to a read-only register");
+		else if ((sr->flags & F_REG_WRITE) && (op_flags & F_REG_READ))
+		  *notes = _("reading from a write-only register");
+	      }
+	  }
+	break;
+      }
 
     case AARCH64_OPND_PSTATEFIELD:
       for (i = 0; aarch64_pstatefields[i].name; ++i)