gdbserver: constify the 'pid_to_exec_file' target op

gdbserver/ChangeLog:
2021-04-12  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* target.h (class process_stratum_target) <pid_to_exec_file>:
	Constify the return type.  Update the definition/references below.
	* target.cc (process_stratum_target::pid_to_exec_file)
	* linux-low.h (class linux_process_target) <pid_to_exec_file>
	* linux-low.cc (linux_process_target::pid_to_exec_file)
	* netbsd-low.h (class netbsd_process_target) <pid_to_exec_file>
	* netbsd-low.cc (netbsd_process_target::pid_to_exec_file)
	* server.cc (handle_qxfer_exec_file)

gdbserver/ChangeLog

@@ -1,3 +1,14 @@
+2021-04-12  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>
+
+	* target.h (class process_stratum_target) <pid_to_exec_file>:
+	Constify the return type.  Update the definition/references below.
+	* target.cc (process_stratum_target::pid_to_exec_file)
+	* linux-low.h (class linux_process_target) <pid_to_exec_file>
+	* linux-low.cc (linux_process_target::pid_to_exec_file)
+	* netbsd-low.h (class netbsd_process_target) <pid_to_exec_file>
+	* netbsd-low.cc (netbsd_process_target::pid_to_exec_file)
+	* server.cc (handle_qxfer_exec_file)
+
 2021-04-11  Eli Zaretskii  <eliz@gnu.org>
 
 	* win32-low.cc (win32_add_dll): New function, with body almost

gdbserver/linux-low.cc

@@ -6265,7 +6265,7 @@ linux_process_target::supports_pid_to_exec_file ()
   return true;
 }
 
-char *
+const char *
 linux_process_target::pid_to_exec_file (int pid)
 {
   return linux_proc_pid_to_exec_file (pid);

gdbserver/linux-low.h

@@ -292,7 +292,7 @@ public:
 
   bool supports_pid_to_exec_file () override;
 
-  char *pid_to_exec_file (int pid) override;
+  const char *pid_to_exec_file (int pid) override;
 
   bool supports_multifs () override;
 

gdbserver/netbsd-low.cc

@@ -1193,10 +1193,10 @@ netbsd_process_target::supports_qxfer_libraries_svr4 ()
 /* Return the name of a file that can be opened to get the symbols for
    the child process identified by PID.  */
 
-char *
+const char *
 netbsd_process_target::pid_to_exec_file (pid_t pid)
 {
-  return const_cast<char *> (netbsd_nat::pid_to_exec_file (pid));
+  return netbsd_nat::pid_to_exec_file (pid);
 }
 
 /* Implementation of the target_ops method "supports_pid_to_exec_file".  */

gdbserver/netbsd-low.h

@@ -121,7 +121,7 @@ public:
 
   bool supports_pid_to_exec_file () override;
 
-  char *pid_to_exec_file (int pid) override;
+  const char *pid_to_exec_file (int pid) override;
 
   const char *thread_name (ptid_t thread) override;
 

gdbserver/server.cc

@@ -1466,7 +1466,6 @@ handle_qxfer_exec_file (const char *annex,
 			gdb_byte *readbuf, const gdb_byte *writebuf,
 			ULONGEST offset, LONGEST len)
 {
-  char *file;
   ULONGEST pid;
   int total_len;
 
@@ -1490,7 +1489,7 @@ handle_qxfer_exec_file (const char *annex,
   if (pid <= 0)
     return -1;
 
-  file = the_target->pid_to_exec_file (pid);
+  const char *file = the_target->pid_to_exec_file (pid);
   if (file == NULL)
     return -1;
 

gdbserver/target.cc

@@ -783,7 +783,7 @@ process_stratum_target::supports_pid_to_exec_file ()
   return false;
 }
 
-char *
+const char *
 process_stratum_target::pid_to_exec_file (int pid)
 {
   gdb_assert_not_reached ("target op pid_to_exec_file not supported");

gdbserver/target.h

@@ -440,7 +440,7 @@ public:
      character string containing the pathname is returned.  This
      string should be copied into a buffer by the client if the string
      will not be immediately used, or if it must persist.  */
-  virtual char *pid_to_exec_file (int pid);
+  virtual const char *pid_to_exec_file (int pid);
 
   /* Return true if any of the multifs ops is supported.  */
   virtual bool supports_multifs ();