[RFA 3/4] Return unique_xmalloc_ptr from gdbscm_safe_eval_string

[Tom Tromey <tom@tromey.com>]

This changes gdbscm_safe_eval_string to return a unique_xmalloc_ptr.
This allows for the removal of some cleanups.  It also fixes a
potential latent memory leak in gdbscm_set_backtrace.

2018-05-26  Tom Tromey  <tom@tromey.com>

	* guile/guile.c (gdbscm_eval_from_control_command): Update.
	* guile/guile-internal.h (gdbscm_safe_eval_string): Update.
	* guile/scm-objfile.c (gdbscm_execute_objfile_script): Update.
	* guile/scm-safe-call.c (gdbscm_safe_eval_string): Return
	unique_xmalloc_ptr.
---
 gdb/ChangeLog              |  8 ++++++++
 gdb/guile/guile-internal.h |  3 ++-
 gdb/guile/guile.c          | 23 +++++------------------
 gdb/guile/scm-objfile.c    | 10 +++-------
 gdb/guile/scm-safe-call.c  |  6 +++---
 5 files changed, 21 insertions(+), 29 deletions(-)

diff --git a/gdb/guile/guile-internal.h b/gdb/guile/guile-internal.h
index 20e2c70e16..2bf0cf72b2 100644
--- a/gdb/guile/guile-internal.h
+++ b/gdb/guile/guile-internal.h
@@ -402,7 +402,8 @@ extern SCM gdbscm_safe_apply_1 (SCM proc, SCM arg0, SCM args,
 
 extern SCM gdbscm_unsafe_call_1 (SCM proc, SCM arg0);
 
-extern char *gdbscm_safe_eval_string (const char *string, int display_result);
+extern gdb::unique_xmalloc_ptr<char> gdbscm_safe_eval_string
+    (const char *string, int display_result);
 
 extern char *gdbscm_safe_source_script (const char *filename);
 
diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c
index 0bbbf6eac1..6b5faa38bc 100644
--- a/gdb/guile/guile.c
+++ b/gdb/guile/guile.c
@@ -197,15 +197,10 @@ guile_command (const char *arg, int from_tty)
 
   if (arg && *arg)
     {
-      char *msg = gdbscm_safe_eval_string (arg, 1);
+      gdb::unique_xmalloc_ptr<char> msg = gdbscm_safe_eval_string (arg, 1);
 
       if (msg != NULL)
-	{
-	  /* It is ok that this is a "dangling cleanup" because we
-	     throw immediately.  */
-	  make_cleanup (xfree, msg);
-	  error ("%s", msg);
-	}
+	error ("%s", msg.get ());
     }
   else
     {
@@ -253,24 +248,16 @@ static void
 gdbscm_eval_from_control_command
   (const struct extension_language_defn *extlang, struct command_line *cmd)
 {
-  char *script, *msg;
-  struct cleanup *cleanup;
+  char *script;
 
   if (cmd->body_list_1 != nullptr)
     error (_("Invalid \"guile\" block structure."));
 
-  cleanup = make_cleanup (null_cleanup, NULL);
-
   script = compute_scheme_string (cmd->body_list_0.get ());
-  msg = gdbscm_safe_eval_string (script, 0);
+  gdb::unique_xmalloc_ptr<char> msg = gdbscm_safe_eval_string (script, 0);
   xfree (script);
   if (msg != NULL)
-    {
-      make_cleanup (xfree, msg);
-      error ("%s", msg);
-    }
-
-  do_cleanups (cleanup);
+    error ("%s", msg.get ());
 }
 
 /* Read a file as Scheme code.
diff --git a/gdb/guile/scm-objfile.c b/gdb/guile/scm-objfile.c
index 9917119084..ccf7c66d33 100644
--- a/gdb/guile/scm-objfile.c
+++ b/gdb/guile/scm-objfile.c
@@ -336,16 +336,12 @@ gdbscm_execute_objfile_script (const struct extension_language_defn *extlang,
 			       struct objfile *objfile, const char *name,
 			       const char *script)
 {
-  char *msg;
-
   ofscm_current_objfile = objfile;
 
-  msg = gdbscm_safe_eval_string (script, 0 /* display_result */);
+  gdb::unique_xmalloc_ptr<char> msg
+    = gdbscm_safe_eval_string (script, 0 /* display_result */);
   if (msg != NULL)
-    {
-      fprintf_filtered (gdb_stderr, "%s", msg);
-      xfree (msg);
-    }
+    fprintf_filtered (gdb_stderr, "%s", msg.get ());
 
   ofscm_current_objfile = NULL;
 }
diff --git a/gdb/guile/scm-safe-call.c b/gdb/guile/scm-safe-call.c
index 2cba399e23..63c4833564 100644
--- a/gdb/guile/scm-safe-call.c
+++ b/gdb/guile/scm-safe-call.c
@@ -393,9 +393,9 @@ scscm_eval_scheme_string (void *datap)
    and preventing continuation capture.
    The result is NULL if no exception occurred.  Otherwise, the exception is
    printed according to "set guile print-stack" and the result is an error
-   message allocated with malloc, caller must free.  */
+   message.  */
 
-char *
+gdb::unique_xmalloc_ptr<char>
 gdbscm_safe_eval_string (const char *string, int display_result)
 {
   struct eval_scheme_string_data data = { string, display_result };
@@ -404,7 +404,7 @@ gdbscm_safe_eval_string (const char *string, int display_result)
   result = gdbscm_with_guile (scscm_eval_scheme_string, (void *) &data);
 
   if (result != NULL)
-    return xstrdup (result);
+    return gdb::unique_xmalloc_ptr<char> (xstrdup (result));
   return NULL;
 }
 \f
-- 
2.13.6