realloc: Introduce a wrapper for realloc along the same lines as free

We also need to wrap realloc() to dispatch pointers to the correct
free/alloc implementation.

capsule/_int_dlopen.h

@@ -42,3 +42,9 @@ _wrapped_free (void *ptr)
     if (ptr)
         capsule_shim_free( cap, ptr );
 }
+
+static void *
+_wrapped_realloc (void *ptr, size_t size)
+{
+    return capsule_shim_realloc( cap, ptr, size );
+}

capsule/capsule-dlmopen.c

@@ -313,6 +313,10 @@ _capsule_load (const capsule cap,
     if( cap->ns->mem->free == NULL )
         cap->ns->mem->free = dlsym( ret, "free" );
 
+    if( cap->ns->mem->realloc == NULL )
+        cap->ns->mem->realloc = dlsym( ret, "realloc" );
+
+    // =====================================================================
     // TODO: failure in the dlopen fixup phase should probably be fatal:
     if( ret      != NULL && // no errors so far
         wrappers != NULL )  // have a dlopen fixup function

capsule/capsule-init.c

@@ -225,7 +225,8 @@ get_capsule_metadata (struct link_map *map, const char *only)
             static const capsule_item no_wrapper = { NULL };
             const capsule_item int_dlopen_wrapper =
             {
-                "dlopen", (capsule_addr) meta->int_dlopen,
+                "dlopen",
+                (capsule_addr) meta->int_dlopen,
                 (capsule_addr) meta->int_dlopen,
             };
 
@@ -236,6 +237,13 @@ get_capsule_metadata (struct link_map *map, const char *only)
                 (capsule_addr) meta->int_free,
             };
 
+            const capsule_item int_realloc_wrapper =
+            {
+                "realloc",
+                (capsule_addr) meta->int_realloc,
+                (capsule_addr) meta->int_realloc,
+            };
+
             cap = xcalloc( 1, sizeof(struct _capsule) );
             cap->ns = get_namespace( meta->default_prefix, meta->soname );
             DEBUG( DEBUG_CAPSULE,
@@ -247,12 +255,24 @@ get_capsule_metadata (struct link_map *map, const char *only)
 
             cap->internal_wrappers[ 0 ] = int_dlopen_wrapper;
             cap->internal_wrappers[ 1 ] = int_free_wrapper;
+            cap->internal_wrappers[ 2 ] = int_realloc_wrapper;
 
-            for( i = 2; alloc_func[ i ].name != NULL; i++ )
+            for( i = 3; alloc_func[ i ].name != NULL; i++ )
             {
+                // pre-populated functions that we should skip are
+                // flagged with an invalid name starting with '-'.
+                // in a properly laid out file they'll all be at the start of
+                // alloc_func and we should never see them, but just in case:
+                if( alloc_func[ i ].name[ 0 ] == '-' )
+                    continue;
+
                 capsule_item *capi = &cap->internal_wrappers[ i ];
                 void        **slot = (void **) alloc_func[ i ].real;
 
+                // the addresses held in alloc_func are actually the
+                // addresses of pointers to the real implementations,
+                // which are populated during capsule_init: we deref
+                // those here:
                 capi->name = alloc_func[ i ].name;
                 capi->shim = capi->real = (capsule_addr) *slot;
             }

capsule/capsule-wrappers.c

@@ -327,6 +327,19 @@ static int address_within_main_heap (ElfW(Addr) addr)
     return 1;
 }
 
+void *
+capsule_shim_realloc (const capsule cap, void *ptr, size_t size)
+{
+    if( !ptr || address_within_main_heap( (ElfW(Addr)) ptr ) )
+        return realloc( ptr, size );
+
+    mchunkptr p = mem2chunk( ptr );
+
+    if( chunk_is_mmapped( p ) || chunk_is_vanilla( p, ptr ) )
+        return realloc( ptr, size );
+
+    return cap->ns->mem->realloc( ptr, size );
+}
 
 void
 capsule_shim_free (const capsule cap, void *ptr)

capsule/capsule.h

@@ -102,6 +102,7 @@ struct _capsule_metadata
     capsule_item *items;
     void *(*int_dlopen) (const char *filename, int flag);
     void  (*int_free) (void *ptr);
+    void *(*int_realloc) (void *ptr, size_t size);
     /*< private >*/
     capsule handle;
 };
@@ -267,3 +268,7 @@ char *capsule_get_prefix(const char *dflt, const char *soname);
  */
 _CAPSULE_PUBLIC
 void capsule_shim_free (const capsule cap, void *ptr);
+
+_CAPSULE_PUBLIC
+void * capsule_shim_realloc (const capsule cap, void *ptr, size_t size);
+

data/capsule-mkstublib

@@ -296,6 +296,7 @@ capsule_metadata capsule_meta =
     .items            = relocs,
     .int_dlopen       = _int_dlopen,
     .int_free         = _wrapped_free,
+    .int_realloc      = _wrapped_realloc,
 };
 
 static void __attribute__ ((constructor)) _capsule_init (void)