gdb: Implement native dumpcore function

Add new API for systems with native kernel support for dumping
a process on demand. Wire it into the gdb's gcore functionality.

gdb/ChangeLog:

       * target.h (supports_dumpcore, dumpcore): New
       function declarations.
       * target.c (supports_dumpcore, dumpcore): New
       functions.
       * target-delegates.c: Rebuild.
       * gcore.c (gcore_command): Use target_supports_dumpcore ()
       and target_dumpcore ().

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2020-08-13  Kamil Rytarowski  <n54@gmx.com>
+
+	* target.h (supports_dumpcore, dumpcore): New
+	function declarations.
+	* target.c (supports_dumpcore, dumpcore): New
+	functions.
+	* target-delegates.c: Rebuild.
+	* gcore.c (gcore_command): Use target_supports_dumpcore ()
+	and target_dumpcore ().
+
 2020-08-13  Aaron Merey  <amerey@redhat.com>
 
 	* debuginfod-support.c: Replace global variables with user_data.

gdb/gcore.c

@@ -145,17 +145,22 @@ gcore_command (const char *args, int from_tty)
 		      "Opening corefile '%s' for output.\n",
 		      corefilename.get ());
 
-  /* Open the output file.  */
-  gdb_bfd_ref_ptr obfd (create_gcore_bfd (corefilename.get ()));
+  if (target_supports_dumpcore ())
+    target_dumpcore (corefilename.get ());
+  else
+    {
+      /* Open the output file.  */
+      gdb_bfd_ref_ptr obfd (create_gcore_bfd (corefilename.get ()));
 
-  /* Arrange to unlink the file on failure.  */
-  gdb::unlinker unlink_file (corefilename.get ());
+      /* Arrange to unlink the file on failure.  */
+      gdb::unlinker unlink_file (corefilename.get ());
 
-  /* Call worker function.  */
-  write_gcore_file (obfd.get ());
+      /* Call worker function.  */
+      write_gcore_file (obfd.get ());
 
-  /* Succeeded.  */
-  unlink_file.keep ();
+      /* Succeeded.  */
+      unlink_file.keep ();
+    }
 
   fprintf_filtered (gdb_stdout, "Saved corefile %s\n", corefilename.get ());
 }

gdb/target-delegates.c

@@ -108,6 +108,8 @@ struct dummy_target : public target_ops
   bool supports_disable_randomization () override;
   bool supports_string_tracing () override;
   bool supports_evaluation_of_breakpoint_conditions () override;
+  bool supports_dumpcore () override;
+  void dumpcore (const char *arg0) override;
   bool can_run_breakpoint_commands () override;
   struct gdbarch *thread_architecture (ptid_t arg0) override;
   struct address_space *thread_address_space (ptid_t arg0) override;
@@ -277,6 +279,8 @@ struct debug_target : public target_ops
   bool supports_disable_randomization () override;
   bool supports_string_tracing () override;
   bool supports_evaluation_of_breakpoint_conditions () override;
+  bool supports_dumpcore () override;
+  void dumpcore (const char *arg0) override;
   bool can_run_breakpoint_commands () override;
   struct gdbarch *thread_architecture (ptid_t arg0) override;
   struct address_space *thread_address_space (ptid_t arg0) override;
@@ -2825,6 +2829,52 @@ debug_target::supports_evaluation_of_breakpoint_conditions ()
   return result;
 }
 
+bool
+target_ops::supports_dumpcore ()
+{
+  return this->beneath ()->supports_dumpcore ();
+}
+
+bool
+dummy_target::supports_dumpcore ()
+{
+  return false;
+}
+
+bool
+debug_target::supports_dumpcore ()
+{
+  bool result;
+  fprintf_unfiltered (gdb_stdlog, "-> %s->supports_dumpcore (...)\n", this->beneath ()->shortname ());
+  result = this->beneath ()->supports_dumpcore ();
+  fprintf_unfiltered (gdb_stdlog, "<- %s->supports_dumpcore (", this->beneath ()->shortname ());
+  fputs_unfiltered (") = ", gdb_stdlog);
+  target_debug_print_bool (result);
+  fputs_unfiltered ("\n", gdb_stdlog);
+  return result;
+}
+
+void
+target_ops::dumpcore (const char *arg0)
+{
+  this->beneath ()->dumpcore (arg0);
+}
+
+void
+dummy_target::dumpcore (const char *arg0)
+{
+}
+
+void
+debug_target::dumpcore (const char *arg0)
+{
+  fprintf_unfiltered (gdb_stdlog, "-> %s->dumpcore (...)\n", this->beneath ()->shortname ());
+  this->beneath ()->dumpcore (arg0);
+  fprintf_unfiltered (gdb_stdlog, "<- %s->dumpcore (", this->beneath ()->shortname ());
+  target_debug_print_const_char_p (arg0);
+  fputs_unfiltered (")\n", gdb_stdlog);
+}
+
 bool
 target_ops::can_run_breakpoint_commands ()
 {

gdb/target.h

@@ -881,6 +881,14 @@ struct target_ops
     virtual bool supports_evaluation_of_breakpoint_conditions ()
       TARGET_DEFAULT_RETURN (false);
 
+    /* Does this target support native dumpcore API?  */
+    virtual bool supports_dumpcore ()
+      TARGET_DEFAULT_RETURN (false);
+
+    /* Generate the core file with native target API.  */
+    virtual void dumpcore (const char *filename)
+      TARGET_DEFAULT_IGNORE ();
+
     /* Does this target support evaluation of breakpoint commands on its
        end?  */
     virtual bool can_run_breakpoint_commands ()
@@ -1499,6 +1507,16 @@ int target_supports_disable_randomization (void);
 #define target_supports_evaluation_of_breakpoint_conditions() \
   (current_top_target ()->supports_evaluation_of_breakpoint_conditions) ()
 
+/* Does this target support dumpcore API?  */
+
+#define target_supports_dumpcore() \
+  (current_top_target ()->supports_dumpcore) ()
+
+/* Generate the core file with target API.  */
+
+#define target_dumpcore(x) \
+  (current_top_target ()->dumpcore (x))
+
 /* Returns true if this target can handle breakpoint commands
    on its end.  */