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Re: Prevent compiler warning on block.c

From: Thomas Huth
Subject: Re: Prevent compiler warning on block.c
Date: Wed, 9 Jun 2021 09:12:26 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0

On 05/05/2021 10.05, Vladimir Sementsov-Ogievskiy wrote:
05.05.2021 10:59, Miroslav Rezanina wrote:
Commit 3108a15cf (block: introduce bdrv_drop_filter()) introduced uninitialized variable to_cow_parent in bdrv_replace_node_common function that is used only when detach_subchain is true. It is used in two places. First if block properly initialize
the variable and second block use it.

However, compiler treats this two blocks as two independent cases so it thinks first block can fail test and second one pass (although both use same condition). This cause
warning that variable can be uninitialized in second block.

To prevent this warning, initialize the variable with NULL.

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
diff --git a/block.c b/block.c
index 874c22c43e..3ca27bd2d9 100644
--- a/block.c
+++ b/block.c
@@ -4851,7 +4851,7 @@ static int bdrv_replace_node_common(BlockDriverState *from,
      Transaction *tran = tran_new();
      g_autoptr(GHashTable) found = NULL;
      g_autoptr(GSList) refresh_list = NULL;
-    BlockDriverState *to_cow_parent;
+    BlockDriverState *to_cow_parent = NULL;
      int ret;

      if (detach_subchain) {

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

This just popped up again here:


Kevin, Max, could you please pick it up to get this problem fixed?


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