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Re: [Qemu-devel] [PATCH v3 2/4] compiler: rework BUG_ON using a struct
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v3 2/4] compiler: rework BUG_ON using a struct |
Date: |
Fri, 20 Jan 2017 08:42:41 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) |
"Michael S. Tsirkin" <address@hidden> writes:
> There are theoretical concerns that some compilers might not trigger
> build failures on attempts to define an array of size -1 and make it a
> variable sized array instead. Let rewrite using a struct with a negative
> bit field size instead as there are no dynamic bit field sizes. This is
> similar to what Linux does.
>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
> include/qemu/compiler.h | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index 7512082..c6f673e 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -85,9 +85,12 @@
> #define typeof_field(type, field) typeof(((type *)0)->field)
> #define type_check(t1,t2) ((t1*)0 - (t2*)0)
>
> -#define QEMU_BUILD_BUG_ON(x) \
> - typedef char glue(qemu_build_bug_on__, __LINE__)[(x) ? -1 : 1] \
> - __attribute__((unused))
> +#define QEMU_BUILD_BUG_ON_STRUCT(x) \
> + struct { \
> + int qemu_build_bug_on : (x) ? -1 : 1; \
> + }
The qemu_build_bug_on name space pollution is harmless, but quite
unnecessary: the name can be simply omitted (unnamed bit-field).
> +#define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
> + glue(qemu_build_bug_on__, __LINE__) __attribute__((unused))
>
> #if defined __GNUC__
> # if !QEMU_GNUC_PREREQ(4, 4)
Re: [Qemu-devel] [PATCH v3 2/4] compiler: rework BUG_ON using a struct, Dr. David Alan Gilbert, 2017/01/20
[Qemu-devel] [PATCH v3 3/4] compiler: expression version of QEMU_BUILD_BUG_ON, Michael S. Tsirkin, 2017/01/19
[Qemu-devel] [PATCH v3 4/4] ARRAY_SIZE: check that argument is an array, Michael S. Tsirkin, 2017/01/19