[PATCH v2 2/7] gdb/aarch64: Add custom printing for POR_EL0

[<srinath.parvathaneni@arm.com>]

From: Srinath Parvathaneni <srinath.parvathaneni@arm.com>

Add custom printing support for the POR_EL0 register when displayed
using `info registers` or `info all-registers`.

The register value is decoded into a human-readable "rwx"
representation for each nibble in the POR_EL0 register, making the
POE permissions easier to interpret.

Example:
(gdb) set $por_el0=0xffffffff77777777
(gdb) info register por_el0
por_el0        0xffffffff77777777  [P15=??? P14=??? P13=??? P12=??? P11=??? P10=??? P9=??? P8=??? P7=rwx P6=rwx P5=rwx P4=rwx P3=rwx P2=rwx P1=rwx P0=rwx ]
---
 gdb/aarch64-tdep.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index f1e1a9c7a19..3ef4e696c7c 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -3135,6 +3135,86 @@ aarch64_pseudo_register_type (struct gdbarch *gdbarch, int regnum)
 		  p_regnum);
 }
 
+/* Convert a POR_EL0 Perm<m> overlay permission encoding into rwx-style string.
+   For example:
+     0b0011 -> "r-x" (3)
+     0b0101 -> "rw-" (5)
+     0b0111 -> "rwx" (7)
+     0b0000 -> "---" (0)
+   Reserved encodings (0b1xxx) are returned as "???".  */
+
+static const char*
+aarch64_perm_overlay_decode (unsigned int perm)
+{
+  switch (perm)
+   {
+     case 0: return "---";
+     case 1: return "r--";
+     case 2: return "--x";
+     case 3: return "r-x";
+     case 4: return "-w-";
+     case 5: return "rw-";
+     case 6: return "-wx";
+     case 7: return "rwx";
+     default: return "???";
+   }
+}
+
+/* Display POE reigster POR_EL0 in the following format for the 'info registers'
+   and 'info all-registers' commands:
+   <register-name> <hex-value> [<decoded per-protection-key permissions>]  */
+
+static void
+aarch64_print_poe_register_info (struct ui_file *file,
+				 int regnum,
+				 const char *name,
+				 const frame_info_ptr &frame)
+{
+  value *val = value_of_register (regnum, get_next_frame_sentinel_okay (frame));
+  ULONGEST por_el0 = (ULONGEST) value_as_long (val);
+  gdb_printf (file, "%-14s 0x%s  [", name, phex_nz (por_el0, 8));
+
+  for (int i = 15; i >= 0; --i)
+    {
+      unsigned int perm = (por_el0 >> (i * 4)) & 0xf;
+      gdb_printf (file, "P%d=%s ", i, aarch64_perm_overlay_decode (perm));
+    }
+
+  gdb_puts ("]\n", file);
+}
+
+/* For 'info registers' and 'info all-registers', print POR_EL0 using the
+   custom POE register printer and all other registers using the default
+   register printer.  */
+
+static void
+aarch64_print_registers_info (struct gdbarch *gdbarch,
+			      struct ui_file *file,
+			      const frame_info_ptr &frame,
+			      int regnum,
+			      bool print_all)
+{
+  const int numregs = gdbarch_num_cooked_regs (gdbarch);
+  aarch64_gdbarch_tdep *tdep = gdbarch_tdep<aarch64_gdbarch_tdep> (gdbarch);
+
+  if (regnum == -1)
+    {
+      for (int i = 0; i < numregs; i++)
+	{
+	  if (i == tdep->poe_regnum)
+	    {
+	      aarch64_print_poe_register_info (file, i, "por_el0", frame);
+	      continue;
+	    }
+	  default_print_registers_info (gdbarch, file, frame,  i, print_all);
+	}
+    }
+  else if (regnum == tdep->poe_regnum)
+    aarch64_print_poe_register_info (file, regnum, "por_el0", frame);
+  else
+    default_print_registers_info (gdbarch, file, frame, regnum, print_all);
+}
+
 /* Implement the "pseudo_register_reggroup_p" tdesc_arch_data method.  */
 
 static bool
@@ -4141,6 +4221,10 @@ aarch64_features_from_target_desc (const struct target_desc *tdesc)
   features.fpmr = (tdesc_find_feature (tdesc, "org.gnu.gdb.aarch64.fpmr")
 		   != nullptr);
 
+  /* Check for POE feature.  */
+  features.poe = (tdesc_find_feature (tdesc, "org.gnu.gdb.aarch64.poe")
+		  != nullptr);
+
   return features;
 }
 
@@ -4774,6 +4858,7 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   tdep->gcs_reg_base = first_gcs_regnum;
   tdep->gcs_linux_reg_base = first_gcs_linux_regnum;
   tdep->fpmr_regnum = fpmr_regnum;
+  tdep->poe_regnum = poe_regnum;
 
   /* Set the SME register set details.  The pseudo-registers will be adjusted
      later.  */
@@ -4816,6 +4901,7 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_tdesc_pseudo_register_reggroup_p (gdbarch,
 					aarch64_pseudo_register_reggroup_p);
   set_gdbarch_cannot_store_register (gdbarch, aarch64_cannot_store_register);
+  set_gdbarch_print_registers_info (gdbarch, aarch64_print_registers_info);
 
   /* Set the allocation tag granule size to 16 bytes.  */
   set_gdbarch_memtag_granule_size (gdbarch, AARCH64_MTE_GRANULE_SIZE);
-- 
2.43.0