Improve error messages for capability reads/writes to memory

Improve the messages a little so the errors are more clear. One case in
particular is when we attempt to write a tagged capability to a shared
mapping area that doesn't support tags.

GDB and GDBserver share the same error messages now.

3 files changed, 59 insertions, 14 deletions

diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
index 5e0e599c735..3848a750939 100644
--- a/gdb/aarch64-linux-nat.c
+++ b/gdb/aarch64-linux-nat.c
@@ -1101,7 +1101,10 @@ aarch64_linux_nat_target::read_capability (CORE_ADDR addr)
   struct user_cap cap;
 
   if (!aarch64_linux_read_capability (tid, addr, cap))
-    perror_with_name (_("Unable to read capability from address."));
+    {
+      gdb::byte_vector cap_vec;
+      return cap_vec;
+    }
 
   gdb::byte_vector cap_vec (17);
   memcpy (cap_vec.data (), &cap.tag, 1);
@@ -1124,8 +1127,7 @@ aarch64_linux_nat_target::write_capability (CORE_ADDR addr,
   memcpy (&cap.val, buffer.data () + 1, 16);
 
   if (!aarch64_linux_write_capability (tid, addr, cap))
-    perror_with_name (_("Unable to write capability to address.\n"
-			"Please run \"sysctl cheri.ptrace_forge_cap=1\"."));
+    return false;
 
   return true;
 }
diff --git a/gdb/nat/aarch64-cap-linux.c b/gdb/nat/aarch64-cap-linux.c
index 1b427803c16..34aa5ec1ac0 100644
--- a/gdb/nat/aarch64-cap-linux.c
+++ b/gdb/nat/aarch64-cap-linux.c
@@ -19,6 +19,50 @@
 #include "aarch64-cap-linux.h"
 #include "gdb_ptrace.h"
 
+/* Helper function to display various possible errors when reading
+   Morello capabilities from memory.  */
+
+static void
+morello_linux_peekcap_error (int error)
+{
+  switch (error)
+    {
+    case EIO:
+    case EFAULT:
+      warning (_("PTRACE_PEEKCAP: Couldn't fetch capability"));
+      break;
+    default:
+      warning (_("PTRACE_PEEKCAP: Unknown error"));
+      break;
+    }
+}
+
+/* Helper function to display various possible errors when writing
+   Morello capabilities to memory.  */
+
+static void
+morello_linux_pokecap_error (int error)
+{
+  switch (error)
+    {
+    case EIO:
+    case EFAULT:
+      warning (_("PTRACE_POKECAP: Couldn't store capability"));
+      break;
+    case EPERM:
+      warning (_("PTRACE_POKECAP:: Couldn't store capability.\n"
+		 "Make sure the sysctl flag cheri.ptrace_forge_cap is 1"));
+      break;
+    case EOPNOTSUPP:
+      warning (_("PTRACE_POKECAP: Capability tags not enabled for"
+		 " requested address"));
+      break;
+    default:
+      warning (_("PTRACE_POKECAP: Unknown error"));
+      break;
+    }
+}
+
 /* See aarch64-cap-linux.h */
 
 bool
@@ -31,7 +75,10 @@ aarch64_linux_read_capability (int tid, CORE_ADDR address,
 
   /* Fetch the tag from ptrace.  */
   if (ptrace (PTRACE_PEEKCAP, tid, address, &cap) < 0)
-    return false;
+    {
+      morello_linux_peekcap_error (errno);
+      return false;
+    }
 
   return true;
 }
@@ -44,7 +91,10 @@ aarch64_linux_write_capability (int tid, CORE_ADDR address,
 {
   /* Fetch the tag from ptrace.  */
   if (ptrace (PTRACE_POKECAP, tid, address, &cap) < 0)
-    return false;
+    {
+      morello_linux_pokecap_error (errno);
+      return false;
+    }
 
   return true;
 }
diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
index 9c2a8349e86..627ddccc5f7 100644
--- a/gdbserver/linux-aarch64-low.cc
+++ b/gdbserver/linux-aarch64-low.cc
@@ -3338,10 +3338,7 @@ aarch64_target::qxfer_capability (const CORE_ADDR address,
   if (readbuf != nullptr)
     {
       if (!aarch64_linux_read_capability (tid, address, cap))
-	{
-	  warning (_("Unable to read capability from address."));
-	  return 0;
-	}
+	return 0;
 
       /* Copy data to readbuf.  */
       memcpy (readbuf, &cap.tag, 1);
@@ -3355,11 +3352,7 @@ aarch64_target::qxfer_capability (const CORE_ADDR address,
       memset (&cap.__reserved, 0, 15);
 
       if (!aarch64_linux_write_capability (tid, address, cap))
-	{
-	  warning (_("Unable to write capability to address.\n"
-		     "Please run \"sysctl cheri.ptrace_forge_cap=1\"."));
-	  return 0;
-	}
+	return 0;
     }
 
   return sizeof (cap.val) + 1;