libxl: make libxl__strdup and libxl__strndup handle NULL

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxl/libxl_internal.c

@@ -161,7 +161,11 @@ char *libxl__sprintf(libxl__gc *gc, const char *fmt, ...)
 
 char *libxl__strdup(libxl__gc *gc, const char *c)
 {
-    char *s = strdup(c);
+    char *s;
+
+    if (!c) return NULL;
+
+    s = strdup(c);
 
     if (!s) libxl__alloc_failed(CTX, __func__, strlen(c), 1);
 
@@ -172,7 +176,11 @@ char *libxl__strdup(libxl__gc *gc, const char *c)
 
 char *libxl__strndup(libxl__gc *gc, const char *c, size_t n)
 {
-    char *s = strndup(c, n);
+    char *s;
+
+    if (!c) return NULL;
+
+    s = strndup(c, n);
 
     if (!s) libxl__alloc_failed(CTX, __func__, n, 1);
 

tools/libxl/libxl_internal.h

@@ -608,9 +608,12 @@ _hidden void *libxl__realloc(libxl__gc *gc_opt, void *ptr, size_t new_size) NN1;
 _hidden char *libxl__sprintf(libxl__gc *gc_opt, const char *fmt, ...) PRINTF_ATTRIBUTE(2, 3) NN1;
 _hidden char *libxl__vsprintf(libxl__gc *gc, const char *format, va_list ap);
 /* duplicate the string @c (similar to a gc'd strdup(3)). */
-_hidden char *libxl__strdup(libxl__gc *gc_opt, const char *c) NN1;
+_hidden char *libxl__strdup(libxl__gc *gc_opt,
+                            const char *c /* may be NULL */) NN1;
 /* duplicate at most @n bytes of string @c (similar to a gc'd strndup(3)). */
-_hidden char *libxl__strndup(libxl__gc *gc_opt, const char *c, size_t n) NN1;
+_hidden char *libxl__strndup(libxl__gc *gc_opt,
+                             const char *c /* may be NULL */,
+                             size_t n) NN1;
 /* strip the last path component from @s and return as a newly allocated
  * string. (similar to a gc'd dirname(3)). */
 _hidden char *libxl__dirname(libxl__gc *gc_opt, const char *s) NN1;