Avoid malloc & memcpy in retro_serialize

libretro.cpp

@@ -2529,6 +2529,7 @@ size_t retro_serialize_size(void)
    StateMem st;
 
    st.data           = NULL;
+   st.data_frontend  = NULL;
    st.loc            = 0;
    st.len            = 0;
    st.malloced       = 0;
@@ -2546,22 +2547,24 @@ bool retro_serialize(void *data, size_t size)
 {
    StateMem st;
    bool ret          = false;
-   uint8_t *_dat     = (uint8_t*)malloc(size);
 
-   if (!_dat)
+   st.data_frontend  = (uint8_t *)data;
-      return false;
+   st.data           = st.data_frontend;
-
-   /* Mednafen can realloc the buffer so we need to ensure this is safe. */
-   st.data           = _dat;
    st.loc            = 0;
    st.len            = 0;
    st.malloced       = size;
    st.initial_malloc = 0;
 
+   /* MDFNSS_SaveSM will malloc separate memory for st.data to complete
+    * the save if the passed-in size is too small */
    ret = MDFNSS_SaveSM(&st, 0, 0, NULL, NULL, NULL);
 
-   memcpy(data, st.data, size);
+   if (st.data != st.data_frontend)
-   free(st.data);
+   {
+      log_cb(RETRO_LOG_WARN, "Save state size has increased\n");
+      free(st.data);
+      ret = false;
+   }
 
    return ret;
 }
@@ -2570,7 +2573,8 @@ bool retro_unserialize(const void *data, size_t size)
 {
    StateMem st;
 
-   st.data           = (uint8_t*)data;
+   st.data_frontend  = (uint8_t *)data;
+   st.data           = st.data_frontend;
    st.loc            = 0;
    st.len            = size;
    st.malloced       = 0;

mednafen/state.c

@@ -54,7 +54,16 @@ static int32_t smem_write(StateMem *st, void *buffer, uint32_t len)
 
       while(newsize < (len + st->loc))
          newsize *= 2;
-      st->data = (uint8_t *)realloc(st->data, newsize);
+
+      /* Don't realloc data_frontend memory */
+      if (st->data == st->data_frontend && st->data != NULL )
+      {
+         st->data = (uint8_t *)malloc(newsize);
+         memcpy(st->data, st->data_frontend, st->malloced);
+      }
+      else
+         st->data = (uint8_t *)realloc(st->data, newsize);
+
       st->malloced = newsize;
    }
    memcpy(st->data + st->loc, buffer, len);

mednafen/state.h

@@ -17,6 +17,7 @@
 typedef struct
 {
    uint8_t *data;
+   uint8_t *data_frontend;  /* never realloc'd */
    uint32_t loc;
    uint32_t len;
    uint32_t malloced;