relocate: avoid memory leaks

[Bruno Haible]

Although relocate() in practice does not produce memory leaks (in the
sense of _repeated_ loss of memory blocks), it is sufficiently often reported
by analysis tools (valgrind, coverity) that I'm now doing something against it.


2017-05-16 Bruno Haible <***@clisp.org>

relocate: Make it easier to reclaim allocated memory.
* lib/relocatable.h (relocate2): New declaration/macro.
* lib/relocatable.c (relocate2): New function.
* doc/relocatable-maint.texi (Supporting Relocation): Mention the
relocate2 function.
* lib/localcharset.c (relocate2): Define fallback.
(get_charset_aliases): Invoke relocate2 instead of relocate. Free the
allocated memory.
* lib/javaversion.c (relocate2): Define fallback.
(javaexec_version): Invoke relocate2 instead of relocate. Free the
allocated memory.

diff --git a/doc/relocatable-maint.texi b/doc/relocatable-maint.texi
index 696b350..50b446b 100644
--- a/doc/relocatable-maint.texi
+++ b/doc/relocatable-maint.texi
@@ -88,6 +88,9 @@ bindtextdomain (PACKAGE, relocate (LOCALEDIR));

The prototype for this function is in @file{relocatable.h}.

+There is also a variant of this function, named @code{relocate2}, that
+makes it easy to reclaim the memory allocated by the call.
+
@item
The @code{set_program_name} function can also configure some
additional libraries to relocate files that they access, by defining
diff --git a/lib/javaversion.c b/lib/javaversion.c
index 817ba0c..f2331aa 100644
--- a/lib/javaversion.c
+++ b/lib/javaversion.c
@@ -23,11 +23,13 @@
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
+#include <stdlib.h>

#if ENABLE_RELOCATABLE
# include "relocatable.h"
#else
# define relocate(pathname) (pathname)
+# define relocate2(pathname,allocatedp) (*(allocatedp) = NULL, (pathname))
#endif

#include "javaexec.h"
@@ -106,7 +108,8 @@ char *
javaexec_version (void)
{
const char *class_name = "javaversion";
- const char *pkgdatadir = relocate (PKGDATADIR);
+ char *malloc_pkgdatadir;
+ const char *pkgdatadir = relocate2 (PKGDATADIR, &malloc_pkgdatadir);
const char *args[1];
struct locals locals;

@@ -115,5 +118,6 @@ javaexec_version (void)
execute_java_class (class_name, &pkgdatadir, 1, true, NULL, args,
false, false, execute_and_read_line, &locals);

+ free (malloc_pkgdatadir);
return locals.line;
}
diff --git a/lib/localcharset.c b/lib/localcharset.c
index 3c2b1ac..6b4f5ae 100644
--- a/lib/localcharset.c
+++ b/lib/localcharset.c
@@ -75,6 +75,7 @@
# include "relocatable.h"
#else
# define relocate(pathname) (pathname)
+# define relocate2(pathname,allocatedp) (*(allocatedp) = NULL, (pathname))
#endif

/* Get LIBDIR. */
@@ -129,6 +130,7 @@ get_charset_aliases (void)
if (cp == NULL)
{
#if !(defined DARWIN7 || defined VMS || defined WINDOWS_NATIVE || defined __CYGWIN__ || defined OS2)
+ char *malloc_dir = NULL;
const char *dir;
const char *base = "charset.alias";
char *file_name;
@@ -137,7 +139,7 @@ get_charset_aliases (void)
necessary for running the testsuite before "make install". */
dir = getenv ("CHARSETALIASDIR");
if (dir == NULL || dir[0] == '\0')
- dir = relocate (LIBDIR);
+ dir = relocate2 (LIBDIR, &malloc_dir);

/* Concatenate dir and base into freshly allocated file_name. */
{
@@ -154,6 +156,8 @@ get_charset_aliases (void)
}
}

+ free (malloc_dir);
+
if (file_name == NULL)
/* Out of memory. Treat the file as empty. */
cp = "";
diff --git a/lib/relocatable.c b/lib/relocatable.c
index 189aee4..0892e3a 100644
--- a/lib/relocatable.c
+++ b/lib/relocatable.c
@@ -573,4 +573,17 @@ relocate (const char *pathname)
return pathname;
}

+/* Returns the pathname, relocated according to the current installation
+ directory.
+ This function sets *ALLOCATEDP to the allocated memory, or to NULL if
+ no memory allocation occurs. So that, after you're done with the return
+ value, to reclaim allocated memory, you can do: free (*ALLOCATEDP). */
+const char *
+relocate2 (const char *pathname, char **allocatedp)
+{
+ const char *result = relocate (pathname);
+ *allocatedp = (result != pathname ? (char *) result : NULL);
+ return result;
+}
+
#endif
diff --git a/lib/relocatable.h b/lib/relocatable.h
index 38d7e68..11bd9ae 100644
--- a/lib/relocatable.h
+++ b/lib/relocatable.h
@@ -52,10 +52,29 @@ extern RELOCATABLE_DLL_EXPORTED void
string that you can free with free() after casting it to 'char *'. */
extern const char * relocate (const char *pathname);

+/* Returns the pathname, relocated according to the current installation
+ directory.
+ This function sets *ALLOCATEDP to the allocated memory, or to NULL if
+ no memory allocation occurs. So that, after you're done with the return
+ value, to reclaim allocated memory, you can do: free (*ALLOCATEDP). */
+extern const char * relocate2 (const char *pathname, char **allocatedp);
+
/* Memory management: relocate() potentially allocates memory, because it has
to construct a fresh pathname. If this is a problem because your program
- calls relocate() frequently, think about caching the result. Or free the
- return value if it was different from the argument pathname. */
+ calls relocate() frequently or because you want to fix all potential memory
+ leaks anyway, you have three options:
+ 1) Use this idiom:
+ const char *pathname = ...;
+ const char *rel_pathname = relocate (pathname);
+ ...
+ if (rel_pathname != pathname)
+ free ((char *) rel_pathname);
+ 2) Use this idiom:
+ char *allocated;
+ const char *rel_pathname = relocate2 (..., &allocated);
+ ...
+ free (allocated);
+ 3) Think about caching the result. */

/* Convenience function:
Computes the current installation prefix, based on the original
@@ -70,6 +89,7 @@ extern char * compute_curr_prefix (const char *orig_installprefix,

/* By default, we use the hardwired pathnames. */
#define relocate(pathname) (pathname)
+#define relocate2(pathname,allocatedp) (*(allocatedp) = NULL, (pathname))

#endif