From: Mark Wielaard <mark@klomp.org>
To: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: elfutils-devel@sourceware.org
Subject: Re: [PATCH RFC 02/11] libasm: Fix xdefault_pattern initialization
Date: Tue, 7 Feb 2023 20:41:22 +0100 [thread overview]
Message-ID: <20230207194122.GC25444@gnu.wildebeest.org> (raw)
In-Reply-To: <20230206222513.1773039-3-iii@linux.ibm.com>
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 <iii@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
next prev parent reply other threads:[~2023-02-07 19:41 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-06 22:25 [PATCH RFC 00/11] Add Memory Sanitizer support Ilya Leoshkevich
2023-02-06 22:25 ` [PATCH RFC 01/11] libdwfl: Fix debuginfod_client redefinition Ilya Leoshkevich
2023-02-07 19:22 ` Mark Wielaard
2023-02-07 19:47 ` Ilya Leoshkevich
2023-02-06 22:25 ` [PATCH RFC 02/11] libasm: Fix xdefault_pattern initialization Ilya Leoshkevich
2023-02-07 19:41 ` Mark Wielaard [this message]
2023-02-07 19:49 ` Ilya Leoshkevich
2023-02-06 22:25 ` [PATCH RFC 03/11] printversion: Fix unused variable Ilya Leoshkevich
2023-02-07 20:44 ` Mark Wielaard
2023-02-08 12:22 ` Ilya Leoshkevich
2023-02-09 14:04 ` Mark Wielaard
2023-02-09 14:57 ` Ilya Leoshkevich
2023-02-06 22:25 ` [PATCH RFC 04/11] readelf: Fix set but not used parameter Ilya Leoshkevich
2023-02-08 16:52 ` Mark Wielaard
2023-02-06 22:25 ` [PATCH RFC 05/11] readelf: Fix set but not used variable Ilya Leoshkevich
2023-02-08 17:09 ` Mark Wielaard
2023-02-06 22:25 ` [PATCH RFC 06/11] Initialize reglocs for VMCOREINFO Ilya Leoshkevich
2023-02-08 17:27 ` Mark Wielaard
2023-02-06 22:25 ` [PATCH RFC 07/11] addr2line: Do not test demangling in run-addr2line-i-test.sh Ilya Leoshkevich
2023-02-08 18:15 ` Mark Wielaard
2023-02-06 22:25 ` [PATCH RFC 08/11] x86_64_return_value_location: Support lvalue and rvalue references Ilya Leoshkevich
2023-02-06 22:25 ` [PATCH RFC 09/11] configure: Use -fno-addrsig if possible Ilya Leoshkevich
2023-02-06 22:25 ` [PATCH RFC 10/11] configure: Add --disable-demangle Ilya Leoshkevich
2023-02-08 18:14 ` Mark Wielaard
2023-02-06 22:25 ` [PATCH RFC 11/11] configure: Add --enable-sanitize-memory Ilya Leoshkevich
2023-02-07 19:05 ` [PATCH RFC 00/11] Add Memory Sanitizer support Mark Wielaard
2023-02-07 19:46 ` Ilya Leoshkevich
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