blob: Don't valgrind assert for defined memory if we aren't writing.

The VK pipeline cache passes a NULL bytes with a nonzero size to a
NULL-data blob to set up the size of the blob.  In this case, we don't
actually execute the memcpy, so the non-existent "bytes" doesn't need to
have defined contents.  Avoids a valgrind warning:

==972858== Unaddressable byte(s) found during client check request
==972858==    at 0x147F4166: blob_write_bytes (blob.c:165)
==972858==    by 0x147F4166: blob_write_bytes (blob.c:158)
==972858==    by 0x14695FFF: vk_pipeline_cache_object_serialize (vk_pipeline_cache.c:240)
[...]
==972858==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

Fixes: 591da9877900 ("vulkan: Add a common VkPipelineCache implementation")
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22617>

diff --git a/src/util/blob.c b/src/util/blob.c
index b293df9..a42e4a4 100644 (file)
--- a/src/util/blob.c
+++ b/src/util/blob.c
@@ -160,10 +160,10 @@ blob_write_bytes(struct blob *blob, const void *bytes, size_t to_write)
    if (! grow_to_fit(blob, to_write))
        return false;
 
-   VG(VALGRIND_CHECK_MEM_IS_DEFINED(bytes, to_write));
-
-   if (blob->data && to_write > 0)
+   if (blob->data && to_write > 0) {
+      VG(VALGRIND_CHECK_MEM_IS_DEFINED(bytes, to_write));
       memcpy(blob->data + blob->size, bytes, to_write);
+   }
    blob->size += to_write;
 
    return true;