[PATCH] Use std::string in substitute_path_component

[PATCH] Use std::string in substitute_path_component

[Tom Tromey]

This changes substitute_path_component to use std::string, simplifying
it quite a bit, and allowing for the removal of an xfree as well.

Regression tested on x86-64 Fedora 36.
---
 gdb/auto-load.c                 | 16 +++++------
 gdb/unittests/utils-selftests.c |  6 ++---
 gdb/utils.c                     | 47 ++++++++++++---------------------
 gdb/utils.h                     |  2 +-
 4 files changed, 26 insertions(+), 45 deletions(-)

diff --git a/gdb/auto-load.c b/gdb/auto-load.c
index 40b05fdc634..6f1548c00c6 100644
--- a/gdb/auto-load.c
+++ b/gdb/auto-load.c
@@ -179,18 +179,14 @@ static std::vector<gdb::unique_xmalloc_ptr<char>> auto_load_safe_path_vec;
 static std::vector<gdb::unique_xmalloc_ptr<char>>
 auto_load_expand_dir_vars (const char *string)
 {
-  char *s = xstrdup (string);
-  substitute_path_component (&s, "$datadir", gdb_datadir.c_str ());
-  substitute_path_component (&s, "$debugdir", debug_file_directory.c_str ());
+  std::string s = string;
+  substitute_path_component (s, "$datadir", gdb_datadir.c_str ());
+  substitute_path_component (s, "$debugdir", debug_file_directory.c_str ());
 
-  if (debug_auto_load && strcmp (s, string) != 0)
-    auto_load_debug_printf ("Expanded $-variables to \"%s\".", s);
+  if (debug_auto_load && s != string)
+    auto_load_debug_printf ("Expanded $-variables to \"%s\".", s.c_str ());
 
-  std::vector<gdb::unique_xmalloc_ptr<char>> dir_vec
-    = dirnames_to_char_ptr_vec (s);
-  xfree(s);
-
-  return dir_vec;
+  return dirnames_to_char_ptr_vec (s.c_str ());
 }
 
 /* Update auto_load_safe_path_vec from current AUTO_LOAD_SAFE_PATH.  */
diff --git a/gdb/unittests/utils-selftests.c b/gdb/unittests/utils-selftests.c
index 70609aa4294..42424b709fe 100644
--- a/gdb/unittests/utils-selftests.c
+++ b/gdb/unittests/utils-selftests.c
@@ -30,10 +30,8 @@ test_substitute_path_component ()
   auto test = [] (std::string s, const char *from, const char *to,
 		  const char *expected)
     {
-      char *temp = xstrdup (s.c_str ());
-      substitute_path_component (&temp, from, to);
-      SELF_CHECK (strcmp (temp, expected) == 0);
-      xfree (temp);
+      substitute_path_component (s, from, to);
+      SELF_CHECK (s == expected);
     };
 
   test ("/abc/$def/g", "abc", "xyz", "/xyz/$def/g");
diff --git a/gdb/utils.c b/gdb/utils.c
index 6ec1cc0d48d..6cadf64a7d2 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -3263,49 +3263,36 @@ parse_pid_to_attach (const char *args)
   return pid;
 }
 
-/* Substitute all occurrences of string FROM by string TO in *STRINGP.  *STRINGP
-   must come from xrealloc-compatible allocator and it may be updated.  FROM
-   needs to be delimited by IS_DIR_SEPARATOR or DIRNAME_SEPARATOR (or be
-   located at the start or end of *STRINGP.  */
+/* Substitute all occurrences of string FROM by string TO in STRINGP.
+   STRINGP may be updated in place.  FROM needs to be delimited by
+   IS_DIR_SEPARATOR or DIRNAME_SEPARATOR (or be located at the start
+   or end of STRINGP).  */
 
 void
-substitute_path_component (char **stringp, const char *from, const char *to)
+substitute_path_component (std::string &stringp, const char *from,
+			   const char *to)
 {
-  char *string = *stringp, *s;
   const size_t from_len = strlen (from);
   const size_t to_len = strlen (to);
 
-  for (s = string;;)
+  for (size_t pos = 0;;)
     {
-      s = strstr (s, from);
-      if (s == NULL)
+      pos = stringp.find (from, pos);
+      if (pos == std::string::npos)
 	break;
 
-      if ((s == string || IS_DIR_SEPARATOR (s[-1])
-	   || s[-1] == DIRNAME_SEPARATOR)
-	  && (s[from_len] == '\0' || IS_DIR_SEPARATOR (s[from_len])
-	      || s[from_len] == DIRNAME_SEPARATOR))
+      if ((pos == 0 || IS_DIR_SEPARATOR (stringp[pos - 1])
+	   || stringp[pos - 1] == DIRNAME_SEPARATOR)
+	  && (pos + from_len == stringp.length ()
+	      || IS_DIR_SEPARATOR (stringp[pos + from_len])
+	      || stringp[pos + from_len] == DIRNAME_SEPARATOR))
 	{
-	  char *string_new;
-
-	  string_new
-	    = (char *) xrealloc (string, (strlen (string) + to_len + 1));
-
-	  /* Relocate the current S pointer.  */
-	  s = s - string + string_new;
-	  string = string_new;
-
-	  /* Replace from by to.  */
-	  memmove (&s[to_len], &s[from_len], strlen (&s[from_len]) + 1);
-	  memcpy (s, to, to_len);
-
-	  s += to_len;
+	  stringp.replace (pos, from_len, to);
+	  pos += to_len;
 	}
       else
-	s++;
+	++pos;
     }
-
-  *stringp = string;
 }
 
 #ifdef HAVE_WAITPID
diff --git a/gdb/utils.h b/gdb/utils.h
index a383036bcfe..bd1daac2e44 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -136,7 +136,7 @@ struct set_batch_flag_and_restore_page_info
 extern int gdb_filename_fnmatch (const char *pattern, const char *string,
 				 int flags);
 
-extern void substitute_path_component (char **stringp, const char *from,
+extern void substitute_path_component (std::string &stringp, const char *from,
 				       const char *to);
 
 std::string ldirname (const char *filename);
-- 
2.39.2

Re: [PATCH] Use std::string in substitute_path_component

[Simon Marchi]

On 4/4/23 14:52, Tom Tromey wrote:
> This changes substitute_path_component to use std::string, simplifying
> it quite a bit, and allowing for the removal of an xfree as well.

Your patch LGTM.

But a random thought I had while reading it: the sole user of
substitute_path_component is auto_load_expand_dir_vars, which splits the
path in components just after that.  It would seem much simpler to do
the $datadir / $debugdir replacement after the split, by iterating on
the vector and checking each element.  Anyway, not a big deal.

Simon

Re: [PATCH] Use std::string in substitute_path_component

[Tom Tromey]

Simon> But a random thought I had while reading it: the sole user of
Simon> substitute_path_component is auto_load_expand_dir_vars, which splits the
Simon> path in components just after that.  It would seem much simpler to do
Simon> the $datadir / $debugdir replacement after the split, by iterating on
Simon> the vector and checking each element.  Anyway, not a big deal.

Good idea, I sent a v2 that does this.

Tom