diff mbox series

[v2,1/7] libasm: Fix xdefault_pattern initialization

Message ID 20230208195226.144143-2-iii@linux.ibm.com
State Committed
Headers
Series Add Memory Sanitizer support |

Commit Message

Ilya Leoshkevich Feb. 8, 2023, 7:52 p.m. UTC 
  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>
---
 libasm/asm_newscn.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

Comments

Mark Wielaard Feb. 9, 2023, 1:14 p.m. UTC | #1 
Hi Ilya,

On Wed, 2023-02-08 at 20:52 +0100, Ilya Leoshkevich wrote:
> 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.
> 

Thanks, pushed.

Mark
diff mbox series

Patch

diff --git a/libasm/asm_newscn.c b/libasm/asm_newscn.c
index d258d969..f28c40f9 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;