From: Bruno Haible <bruno@clisp.org>
Date: Wed, 29 Jul 2026 22:57:30 +0000 (+0200)
Subject: libxml: Fix an ISO C undefined behaviour.
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;p=thirdparty%2Fgettext.git

libxml: Fix an ISO C undefined behaviour.

ISO C 23 § 6.5.7.(10) has requirements for pointer subtraction.

Found by use of Fil-C.

* gnulib-local/lib/libxml/parser.c (xmlParseStartTag2): Avoid invalid pointer
subtraction.
---

diff --git a/gnulib-local/lib/libxml/parser.c b/gnulib-local/lib/libxml/parser.c
index d485a58b8..721904274 100644
--- a/gnulib-local/lib/libxml/parser.c
+++ b/gnulib-local/lib/libxml/parser.c
@@ -1,5 +1,5 @@
 /* libxml2 - Library for parsing XML documents
- * Copyright (C) 2006-2019 Free Software Foundation, Inc.
+ * Copyright (C) 2006-2026 Free Software Foundation, Inc.
  *
  * This file is not part of the GNU gettext program, but is used with
  * GNU gettext.
@@ -9460,12 +9460,11 @@ next_attr:
         if (atts[i+2] != NULL) {
             /*
              * Arithmetic on dangling pointers is technically undefined
-             * behavior, but well...
+             * behavior. Therefore:
              */
-            ptrdiff_t offset = ctxt->input->base - atts[i+2];
+            atts[i+3] = ctxt->input->base + (atts[i+3] - atts[i+2]); /* value */
+            atts[i+4] = ctxt->input->base + (atts[i+4] - atts[i+2]); /* valuend */
             atts[i+2]  = NULL;    /* Reset repurposed namespace URI */
-            atts[i+3] += offset;  /* value */
-            atts[i+4] += offset;  /* valuend */
         }
     }