From c27fa399042f466080e79bb4fd8a4871bc0bcf28 Mon Sep 17 00:00:00 2001
From: Nick Terrell <terrelln@meta.com>
Date: Thu, 24 Aug 2023 16:33:42 -0700
Subject: [PATCH] Work around nullptr-with-nonzero-offset warning

See comment.
---
 lib/decompress/zstd_decompress.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/decompress/zstd_decompress.c b/lib/decompress/zstd_decompress.c
index 94eb95151..ccfd84fa4 100644
--- a/lib/decompress/zstd_decompress.c
+++ b/lib/decompress/zstd_decompress.c
@@ -1548,6 +1548,12 @@ size_t ZSTD_decompressBegin(ZSTD_DCtx* dctx)
     dctx->stage = ZSTDds_getFrameHeaderSize;
     dctx->processedCSize = 0;
     dctx->decodedSize = 0;
+    /* Set to non-null because ZSTD_prefetchMatch() may end up doing addition
+     * with this value for corrupted frames. However, it then just passes the
+     * pointer to PREFETCH_L1(), which doesn't require valid pointers. But,
+     * if it is NULL we get nullptr-with-nonzero-offset UBSAN warnings.
+     */
+    dctx->previousDstEnd = "";
     dctx->previousDstEnd = NULL;
     dctx->prefixStart = NULL;
     dctx->virtualStart = NULL;