[PATCH v1] gdb/linux-tdep: display ProtectionKey in info proc mappings

[PATCH v1] gdb/linux-tdep: display ProtectionKey in info proc mappings

[Matthieu Longo]

Memory Protection Keys provide a mechanism for enforcing page-based
protections without requiring modification of the page tables
when an application changes protection domains. [1]

The "ProtectionKey" field may be present in /proc/PID/smaps on x86_64,
PowerPC, and AArch64 systems since Linux 4.9, when the kernel is built
with Memory Protection Keys support.

Store the parsed PKey in smaps_data as an optional value on systems
where the kernel reports memory protection keys.

Parse /proc/PID/smaps alongside /proc/PID/maps when printing 'info
proc mappings', and add a PKey column when at least one smaps entry
contains a "ProtectionKey" field.
This lets 'info proc mappings' show the protection key associated with
each mapped address range.

[1]: https://docs.kernel.org/core-api/protection-keys.html,
     https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
     linux.git/commit/?id=c1192f842841
---
 gdb/linux-tdep.c | 93 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 78 insertions(+), 15 deletions(-)

diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index 2e9cb14d5bf..2cdf93f3193 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -124,6 +124,7 @@ struct smaps_data
 
   ULONGEST rss;
   ULONGEST swap;
+  std::optional<int> pkey;
 };
 
 /* Whether to take the /proc/PID/coredump_filter into account when
@@ -907,6 +908,11 @@ extract_string_view_from_buffer (gdb::array_view<char> &buffer,
   return {gdb::array_view<char> (start, it), next_start};
 }
 
+/* Forward declaration of parse_smaps_data used in linux_info_proc below.  */
+
+static std::vector<struct smaps_data>
+parse_smaps_data (const file_reader_t<char> &freader);
+
 /* Implement the "info proc" command.  */
 
 static void
@@ -1010,33 +1016,69 @@ linux_info_proc (struct gdbarch *gdbarch, const char *args,
     }
   if (mappings_f)
     {
+      /* Parse the content of /proc/PID/smaps.  */
+      bool pkey_column = false;
+      std::vector<struct smaps_data> smaps_data;
+      file_reader_t<char> smaps_freader
+	(string_printf ("/proc/%ld/smaps", ptid.lwp ()));
+      if (smaps_freader.error ())
+	warning (_("unable to open /proc file '%s'"),
+		 smaps_freader.c_filepath ());
+      else if (smaps_freader)
+	{
+	  smaps_data = parse_smaps_data (smaps_freader);
+
+	  /* Check whether "ProtectionKey" field is present.  */
+	  pkey_column
+	    = std::any_of (smaps_data.cbegin (), smaps_data.cend (),
+			   [] (const struct smaps_data &d) -> bool
+			   { return d.pkey.has_value (); });
+	}
+
+      /* Parse the content of /proc/PID/maps.  */
+      std::vector<struct mapping> maps_data;
       file_reader_t<char> map_freader
 	(string_printf ("/proc/%ld/maps", ptid.lwp ()));
-      if (map_freader)
+      if (map_freader.error ())
+	warning (_("unable to open /proc file '%s'"),
+		 map_freader.c_filepath ());
+      else if (map_freader)
+	{
+	  auto content = map_freader.view ();
+	  for (auto it = content.begin (); it != content.end ();)
+	    {
+	      auto [line, next_line_begin]
+		= extract_string_view_from_buffer (content, it, '\n');
+	      it = next_line_begin;
+
+	      /* read_mapping() expects a null-terminated string.  */
+	      *std::prev (it) = '\0';
+	      maps_data.emplace_back (read_mapping (line.data ()));
+	   }
+	}
+
+      gdb_assert (maps_data.size () == smaps_data.size ());
+
+      if (maps_data.size () > 0)
 	{
 	  gdb_printf (_("Mapped address spaces:\n\n"));
-	  ui_out_emit_table emitter (current_uiout, 6, -1, "ProcMappings");
+	  int n_cols = (pkey_column ? 7 : 6);
+	  ui_out_emit_table emitter (current_uiout, n_cols, -1, "ProcMappings");
 
 	  int width = gdbarch_addr_bit (gdbarch) == 32 ? 10 : 18;
 	  current_uiout->table_header (width, ui_left, "start", "Start Addr");
 	  current_uiout->table_header (width, ui_left, "end", "End Addr");
 	  current_uiout->table_header (width, ui_left, "size", "Size");
 	  current_uiout->table_header (width, ui_left, "offset", "Offset");
+	  if (pkey_column)
+	    current_uiout->table_header (4, ui_left, "pkey", "PKey");
 	  current_uiout->table_header (5, ui_left, "perms", "Perms");
 	  current_uiout->table_header (0, ui_left, "objfile", "File");
 	  current_uiout->table_body ();
 
-	  auto content = map_freader.view ();
-	  for (auto it = content.begin (); it != content.end ();)
+	  auto it_smaps = smaps_data.cbegin ();
+	  for (const auto &m: maps_data)
 	    {
-	      auto [line, next_line_begin]
-		= extract_string_view_from_buffer (content, it, '\n');
-	      it = next_line_begin;
-
-	      /* read_mapping() expects a null-terminated string.  */
-	      *std::prev (it) = '\0';
-	      struct mapping m = read_mapping (line.data ());
-
 	      ui_out_emit_tuple tuple_emitter (current_uiout, nullptr);
 	      current_uiout->field_core_addr ("start", gdbarch, m.addr);
 	      current_uiout->field_core_addr ("end", gdbarch, m.endaddr);
@@ -1047,15 +1089,21 @@ linux_info_proc (struct gdbarch *gdbarch, const char *args,
 						     m.endaddr - m.addr));
 	      current_uiout->field_string ("offset",
 					   paddress (gdbarch, m.offset));
+	      if (pkey_column)
+		{
+		  if (it_smaps->pkey.has_value ())
+		    current_uiout->field_signed ("pkey",
+						 it_smaps->pkey.value ());
+		  else
+		    current_uiout->field_skip ("pkey");
+		}
 	      current_uiout->field_string ("perms", m.permissions);
 	      current_uiout->field_string ("objfile", m.filename,
 					   file_name_style.style ());
 	      current_uiout->text ("\n");
+	      ++it_smaps;
 	    }
 	}
-      else
-	warning (_("unable to open /proc file '%s'"),
-		 map_freader.c_filepath ());
     }
   if (status_f)
     {
@@ -1605,6 +1653,7 @@ parse_smaps_data (const file_reader_t<char> &freader)
       int mapping_file_p;
       ULONGEST rss = -1;
       ULONGEST swap = -1;
+      int pkey = -1;
 
       memset (&v, 0, sizeof (v));
       struct mapping m = read_mapping (line);
@@ -1705,6 +1754,18 @@ parse_smaps_data (const file_reader_t<char> &freader)
 		  mapping_anon_p = 1;
 		}
 	    }
+
+	  if (streq (keyword, "ProtectionKey:"))
+	    {
+	      if (sscanf (line, "%*s%d", &pkey) != 1)
+		{
+		  /* Remove the trailing column when printing the warning.  */
+		  keyword[sizeof ("ProtectionKey:") - 2] = '\0';
+		  warning (_("Error parsing %s's value in {s,}maps file '%s'"),
+			   keyword, freader.c_filepath ());
+		  break;
+		}
+	    }
 	}
       /* Save the smaps entry to the vector.  */
 	struct smaps_data map;
@@ -1724,6 +1785,8 @@ parse_smaps_data (const file_reader_t<char> &freader)
 	map.inode = m.inode;
 	map.rss = rss;
 	map.swap = swap;
+	if (pkey != -1)
+	  map.pkey.emplace (pkey);
 
 	smaps.emplace_back (map);
     }
-- 
2.55.0

Re: [PATCH v1] gdb/linux-tdep: display ProtectionKey in info proc mappings

[Matthieu Longo]

On 28/07/2026 16:29, Matthieu Longo wrote:
> Memory Protection Keys provide a mechanism for enforcing page-based
> protections without requiring modification of the page tables
> when an application changes protection domains. [1]
> 
> The "ProtectionKey" field may be present in /proc/PID/smaps on x86_64,
> PowerPC, and AArch64 systems since Linux 4.9, when the kernel is built
> with Memory Protection Keys support.
> 
> Store the parsed PKey in smaps_data as an optional value on systems
> where the kernel reports memory protection keys.
> 
> Parse /proc/PID/smaps alongside /proc/PID/maps when printing 'info
> proc mappings', and add a PKey column when at least one smaps entry
> contains a "ProtectionKey" field.
> This lets 'info proc mappings' show the protection key associated with
> each mapped address range.
> 
> [1]: https://docs.kernel.org/core-api/protection-keys.html,
>      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
>      linux.git/commit/?id=c1192f842841
> ---
Please, note that this patch has a dependency on the new class file_reader_t introduced in
https://inbox.sourceware.org/gdb-patches/20260728151700.253720-1-matthieu.longo@arm.com/

Matthieu