gdb: testsuite: Test whether PC register is expedited in gdb.server/server-run.exp

One thing GDB always does when the inferior stops is finding out where
it's stopped at, by way of querying the value of the program counter
register.

To save a packet round trip, the remote target can send the PC
value (often alongside other frequently consulted registers such as the
stack pointer) in the stop reply packet as an "expedited register".

Test that this is actually done for the targets where gdbserver is
supposed to.

Extend the "maintenance print remote-registers" command output with an
"Expedited" column which says "yes" if the register was seen by GDB in
the last stop reply packet it received, and is left blank otherwise.

Tested for regressions on aarch64-linux-gnu native-extended-remote.

The testcase was tested on aarch64-linux-gnu, i686-linux-gnu and
x86_64-linux-gnu native-remote and native-extended-remote targets.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Tom Tromey <tom@tromey.com>

6 files changed, 87 insertions, 8 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 5e0ac31..26dd4de 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -90,6 +90,11 @@ save gdb-index
   it contains white space or quote characters.  If the argument
   contains no such special characters then quoting is not required.
 
+maintenance print remote-registers
+  Add an "Expedited" column to the output of the command.  It indicates
+  which registers were included in the last stop reply packet received by
+  GDB.
+
 * New remote packets
 
 vFile:stat
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 891344b..143e498 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -42082,7 +42082,11 @@ including registers which aren't available on the target nor visible
 to user; the command @code{maint print register-groups} includes the
 groups that each register is a member of; and the command @code{maint
 print remote-registers} includes the remote target's register numbers
-and offsets in the `G' packets.
+and offsets in the `G' packets, as well as an indication of which
+registers were included in the last stop reply packet received by
+@value{GDBN} (@pxref{Stop Reply Packets}).  Please note that the list
+of registers included in a stop reply can change from one stop to the
+next.
 
 These commands take an optional parameter, a file name to which to
 write the information.
diff --git a/gdb/regcache-dump.c b/gdb/regcache-dump.c
index bc665dc..6b711bf 100644
--- a/gdb/regcache-dump.c
+++ b/gdb/regcache-dump.c
@@ -162,7 +162,7 @@ protected:
   {
     if (regnum < 0)
       {
-	gdb_printf (file, "Rmt Nr  g/G Offset");
+	gdb_printf (file, "Rmt Nr  g/G Offset  Expedited");
       }
     else if (regnum < gdbarch_num_regs (m_gdbarch))
       {
@@ -170,7 +170,12 @@ protected:
 
 	if (remote_register_number_and_offset (m_gdbarch, regnum,
 					       &pnum, &poffset))
-	  gdb_printf (file, "%7d %11d", pnum, poffset);
+	  {
+	    if (remote_register_is_expedited (regnum))
+	      gdb_printf (file, "%7d %11d  yes", pnum, poffset);
+	    else
+	      gdb_printf (file, "%7d %11d", pnum, poffset);
+	  }
       }
   }
 };
@@ -324,9 +329,11 @@ _initialize_regcache_dump ()
 	     "Takes an optional file parameter."),
 	   &maintenanceprintlist);
   add_cmd ("remote-registers", class_maintenance,
-	   maintenance_print_remote_registers, _("\
-Print the internal register configuration including remote register number "
-"and g/G packets offset.\n\
-Takes an optional file parameter."),
+	   maintenance_print_remote_registers,
+	   _("Print the internal register configuration including remote "
+	     "register number and g/G packets offset.\n"
+	     "Also prints which registers were sent in the last stop reply "
+	     "packet (i.e. expedited).\n"
+	     "Takes an optional file parameter."),
 	   &maintenanceprintlist);
 }
diff --git a/gdb/remote.c b/gdb/remote.c
index 8e704a7..4ec25ee 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -696,6 +696,10 @@ public: /* data */
      qSupported.  */
   gdb_thread_options supported_thread_options = 0;
 
+  /* Contains the regnums of the expedited registers in the last stop
+     reply packet.  */
+  std::set<int> last_seen_expedited_registers;
+
 private:
   /* Asynchronous signal handle registered as event loop source for
      when we have pending events ready to be passed to the core.  */
@@ -1493,6 +1497,20 @@ is_remote_target (process_stratum_target *target)
   return as_remote_target (target) != nullptr;
 }
 
+/* See remote.h.  */
+
+bool
+remote_register_is_expedited (int regnum)
+{
+  remote_target *rt = as_remote_target (current_inferior ()->process_target ());
+
+  if (rt == nullptr)
+    return false;
+
+  remote_state *rs = rt->get_remote_state ();
+  return rs->last_seen_expedited_registers.count (regnum) > 0;
+}
+
 /* Per-program-space data key.  */
 static const registry<program_space>::key<char, gdb::xfree_deleter<char>>
   remote_pspace_data;
@@ -8523,6 +8541,10 @@ remote_target::process_stop_reply (stop_reply_up stop_reply,
 {
   *status = stop_reply->ws;
   ptid_t ptid = stop_reply->ptid;
+  struct remote_state *rs = get_remote_state ();
+
+  /* Forget about last reply's expedited registers.  */
+  rs->last_seen_expedited_registers.clear ();
 
   /* If no thread/process was reported by the stub then select a suitable
      thread/process.  */
@@ -8549,7 +8571,10 @@ remote_target::process_stop_reply (stop_reply_up stop_reply,
 					stop_reply->arch);
 
 	  for (cached_reg_t &reg : stop_reply->regcache)
-	    regcache->raw_supply (reg.num, reg.data.get ());
+	    {
+	      regcache->raw_supply (reg.num, reg.data.get ());
+	      rs->last_seen_expedited_registers.insert (reg.num);
+	    }
 	}
 
       remote_thread_info *remote_thr = get_remote_thread_info (this, ptid);
diff --git a/gdb/remote.h b/gdb/remote.h
index cb0a66d..bfe3c65 100644
--- a/gdb/remote.h
+++ b/gdb/remote.h
@@ -121,4 +121,9 @@ extern void send_remote_packet (gdb::array_view<const char> &buf,
 
 extern bool is_remote_target (process_stratum_target *target);
 
+/* Return true if REGNUM was returned as an expedited register in the last
+   stop reply we received.  */
+
+extern bool remote_register_is_expedited (int regnum);
+
 #endif
diff --git a/gdb/testsuite/gdb.server/server-run.exp b/gdb/testsuite/gdb.server/server-run.exp
index 92eb38b..af5a5f5 100644
--- a/gdb/testsuite/gdb.server/server-run.exp
+++ b/gdb/testsuite/gdb.server/server-run.exp
@@ -52,3 +52,36 @@ if { [istarget *-*-linux*] } {
 
 gdb_breakpoint main
 gdb_test "continue" "Breakpoint.* main .*" "continue to main"
+
+if { [istarget "aarch64*-*-*"]
+     || [istarget "arm*-*-*"]
+     || [istarget "csky*-*-*"]
+     || [istarget "loongarch*-*-*"]
+     || [istarget "riscv*-*-*"] } {
+    set pc_regname "pc"
+} elseif { [is_amd64_regs_target] } {
+    set pc_regname "rip"
+} elseif { [is_x86_like_target] } {
+    set pc_regname "eip"
+} elseif { [istarget "tic6x-*-*"] } {
+    set pc_regname "PC"
+}
+
+# Sending the PC register in advance is good practice.  Test that this is
+# actually done for the targets where gdbserver is supposed to.
+set expedited_pc_test_name "send PC as expedited register in stop reply"
+if { [info exists pc_regname] } {
+    set seen_line false
+    gdb_test_multiple "maintenance print remote-registers" \
+	     $expedited_pc_test_name -lbl {
+	-re " ${pc_regname}\[\[:space:\]\]+${decimal}.*${decimal}  yes" {
+	    set seen_line true
+	    exp_continue
+	}
+	-re "\r\n$gdb_prompt $" {
+	    gdb_assert { $seen_line } $gdb_test_name
+	}
+    }
+} else {
+    untested $expedited_pc_test_name
+}