Hi Ilya,
On Mon, Feb 06, 2023 at 11:25:04PM +0100, Ilya Leoshkevich via Elfutils-devel
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.
>
> Signed-off-by: Ilya Leoshkevich <i...@linux.ibm.com>
> ---
> libasm/asm_newscn.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/libasm/asm_newscn.c b/libasm/asm_newscn.c
> index d258d969..32a3b598 100644
> --- a/libasm/asm_newscn.c
> +++ b/libasm/asm_newscn.c
> @@ -43,17 +43,16 @@
> /* 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
> +static const union
> {
> struct FillPattern pattern;
> - char zero;
> + char zeroes[sizeof(struct FillPattern) + 1];
> } xdefault_pattern =
> {
> .pattern =
> {
> .len = 1
> },
> - .zero = '\0'
> };
Yes, I think this works. Could you update the comment just before this
with some of the commit message explanation? Your explanation is much
better than "play some dirty trick" :)
> const struct FillPattern *__libasm_default_pattern =
> &xdefault_pattern.pattern;
I am surprised this doesn't need a cast. Do you know why?
Thanks,
Mark
