From: Ilya Leoshkevich <iii@linux.ibm.com>
Date: Wed, 8 Feb 2023 19:52:20 +0000 (+0100)
Subject: libasm: Fix xdefault_pattern initialization
X-Git-Tag: elfutils-0.189~27
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=61b99b89f5419cf5be6dd3350ad0b01caabc7447;p=thirdparty%2Felfutils.git

libasm: Fix xdefault_pattern initialization

clang complains:

    asm_newscn.c:48:22: error: field 'pattern' with variable sized type 'struct FillPattern' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
      struct FillPattern pattern;
                         ^

Fix by using a union instead. Define the second union member to be a
char array 1 byte larger than struct FillPattern. This should be legal
according to 6.7.9:

    If an object that has static or thread storage duration is not
    initialized explicitly, then ... if it is a union, the first named
    member is initialized (recursively) according to these rules, and
    any padding is initialized to zero bits.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---

diff --git a/libasm/asm_newscn.c b/libasm/asm_newscn.c
index d258d969f..f28c40f96 100644
--- a/libasm/asm_newscn.c
+++ b/libasm/asm_newscn.c
@@ -41,19 +41,25 @@
 
 
 /* Memory for the default pattern.  The type uses a flexible array
-   which does work well with a static initializer.  So we play some
-   dirty tricks here.  */
-static const struct
+   which does work well with a static initializer.  Work around this by
+   wrapping it in a union, whose second member is a char array 1 byte larger
+   than struct FillPattern.  According to 6.7.9, this does what we need:
+
+        If an object that has static or thread storage duration is not
+        initialized explicitly, then ... if it is a union, the first named
+        member is initialized (recursively) according to these rules, and
+        any padding is initialized to zero bits.  */
+
+static const union
 {
   struct FillPattern pattern;
-  char zero;
+  char zeroes[sizeof(struct FillPattern) + 1];
 } xdefault_pattern =
   {
     .pattern =
     {
       .len = 1
     },
-    .zero = '\0'
   };
 const struct FillPattern *__libasm_default_pattern = &xdefault_pattern.pattern;