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  3. [PATCH v4 0/3] Enable clang build on Windows
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[PATCH v4 1/3] win32: remove usage of attribute gcc_struct

Pierrick Bouvier posted 3 patches 2 months, 3 weeks ago
[PATCH v4 1/3] win32: remove usage of attribute gcc_struct
Posted by Pierrick Bouvier 2 months, 3 weeks ago 
This attribute is not recognized by clang.

An investigation has been performed to ensure this attribute has no
effect on layout of structures we use in QEMU [1], so it's safe to
remove now.

In the future, we'll forbid introducing new bitfields in packed struct,
as they are the one potentially impacted by this change.

[1] https://lore.kernel.org/qemu-devel/66c346de-7e20-4831-b3eb-1cda83240af9@linaro.org/

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 meson.build                               | 5 -----
 include/qemu/compiler.h                   | 7 +------
 scripts/cocci-macro-file.h                | 6 +-----
 subprojects/libvhost-user/libvhost-user.h | 6 +-----
 4 files changed, 3 insertions(+), 21 deletions(-)

diff --git a/meson.build b/meson.build
index d06f59095c6..da279cc1124 100644
--- a/meson.build
+++ b/meson.build
@@ -377,11 +377,6 @@ elif host_os == 'sunos'
   qemu_common_flags += '-D__EXTENSIONS__'
 elif host_os == 'haiku'
   qemu_common_flags += ['-DB_USE_POSITIVE_POSIX_ERRORS', '-D_BSD_SOURCE', '-fPIC']
-elif host_os == 'windows'
-  if not compiler.compiles('struct x { int y; } __attribute__((gcc_struct));',
-                           args: '-Werror')
-    error('Your compiler does not support __attribute__((gcc_struct)) - please use GCC instead of Clang')
-  endif
 endif
 
 # Choose instruction set (currently x86-only)
diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index c06954ccb41..d904408e5ed 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -22,12 +22,7 @@
 #define QEMU_EXTERN_C extern
 #endif
 
-#if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
-# define QEMU_PACKED __attribute__((gcc_struct, packed))
-#else
-# define QEMU_PACKED __attribute__((packed))
-#endif
-
+#define QEMU_PACKED __attribute__((packed))
 #define QEMU_ALIGNED(X) __attribute__((aligned(X)))
 
 #ifndef glue
diff --git a/scripts/cocci-macro-file.h b/scripts/cocci-macro-file.h
index d247a5086e9..c64831d5408 100644
--- a/scripts/cocci-macro-file.h
+++ b/scripts/cocci-macro-file.h
@@ -23,11 +23,7 @@
 #define G_GNUC_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
 #define G_GNUC_NULL_TERMINATED __attribute__((sentinel))
 
-#if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
-# define QEMU_PACKED __attribute__((gcc_struct, packed))
-#else
-# define QEMU_PACKED __attribute__((packed))
-#endif
+#define QEMU_PACKED __attribute__((packed))
 
 #define cat(x,y) x ## y
 #define cat2(x,y) cat(x,y)
diff --git a/subprojects/libvhost-user/libvhost-user.h b/subprojects/libvhost-user/libvhost-user.h
index deb40e77b3f..2ffc58c11b1 100644
--- a/subprojects/libvhost-user/libvhost-user.h
+++ b/subprojects/libvhost-user/libvhost-user.h
@@ -186,11 +186,7 @@ typedef struct VhostUserShared {
     unsigned char uuid[UUID_LEN];
 } VhostUserShared;
 
-#if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
-# define VU_PACKED __attribute__((gcc_struct, packed))
-#else
-# define VU_PACKED __attribute__((packed))
-#endif
+#define VU_PACKED __attribute__((packed))
 
 typedef struct VhostUserMsg {
     int request;
-- 
2.39.5
Re: [PATCH v4 1/3] win32: remove usage of attribute gcc_struct
Posted by Michael S. Tsirkin 2 months, 3 weeks ago 
On Fri, Jan 10, 2025 at 12:33:59PM -0800, Pierrick Bouvier wrote:
> This attribute is not recognized by clang.
> 
> An investigation has been performed to ensure this attribute has no
> effect on layout of structures we use in QEMU [1], so it's safe to
> remove now.
> 
> In the future, we'll forbid introducing new bitfields in packed struct,
> as they are the one potentially impacted by this change.
> 
> [1] https://lore.kernel.org/qemu-devel/66c346de-7e20-4831-b3eb-1cda83240af9@linaro.org/
> Reviewed-by: Thomas Huth <thuth@redhat.com>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Acked-by: Stefano Garzarella <sgarzare@redhat.com>
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
>  meson.build                               | 5 -----
>  include/qemu/compiler.h                   | 7 +------
>  scripts/cocci-macro-file.h                | 6 +-----
>  subprojects/libvhost-user/libvhost-user.h | 6 +-----
>  4 files changed, 3 insertions(+), 21 deletions(-)
> 
> diff --git a/meson.build b/meson.build
> index d06f59095c6..da279cc1124 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -377,11 +377,6 @@ elif host_os == 'sunos'
>    qemu_common_flags += '-D__EXTENSIONS__'
>  elif host_os == 'haiku'
>    qemu_common_flags += ['-DB_USE_POSITIVE_POSIX_ERRORS', '-D_BSD_SOURCE', '-fPIC']
> -elif host_os == 'windows'
> -  if not compiler.compiles('struct x { int y; } __attribute__((gcc_struct));',
> -                           args: '-Werror')
> -    error('Your compiler does not support __attribute__((gcc_struct)) - please use GCC instead of Clang')
> -  endif
>  endif
>  
>  # Choose instruction set (currently x86-only)
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index c06954ccb41..d904408e5ed 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -22,12 +22,7 @@
>  #define QEMU_EXTERN_C extern
>  #endif
>  
> -#if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
> -# define QEMU_PACKED __attribute__((gcc_struct, packed))
> -#else
> -# define QEMU_PACKED __attribute__((packed))
> -#endif
> -
> +#define QEMU_PACKED __attribute__((packed))
>  #define QEMU_ALIGNED(X) __attribute__((aligned(X)))
>  
>  #ifndef glue
> diff --git a/scripts/cocci-macro-file.h b/scripts/cocci-macro-file.h
> index d247a5086e9..c64831d5408 100644
> --- a/scripts/cocci-macro-file.h
> +++ b/scripts/cocci-macro-file.h
> @@ -23,11 +23,7 @@
>  #define G_GNUC_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
>  #define G_GNUC_NULL_TERMINATED __attribute__((sentinel))
>  
> -#if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
> -# define QEMU_PACKED __attribute__((gcc_struct, packed))
> -#else
> -# define QEMU_PACKED __attribute__((packed))
> -#endif
> +#define QEMU_PACKED __attribute__((packed))
>  
>  #define cat(x,y) x ## y
>  #define cat2(x,y) cat(x,y)
> diff --git a/subprojects/libvhost-user/libvhost-user.h b/subprojects/libvhost-user/libvhost-user.h
> index deb40e77b3f..2ffc58c11b1 100644
> --- a/subprojects/libvhost-user/libvhost-user.h
> +++ b/subprojects/libvhost-user/libvhost-user.h
> @@ -186,11 +186,7 @@ typedef struct VhostUserShared {
>      unsigned char uuid[UUID_LEN];
>  } VhostUserShared;
>  
> -#if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
> -# define VU_PACKED __attribute__((gcc_struct, packed))
> -#else
> -# define VU_PACKED __attribute__((packed))
> -#endif
> +#define VU_PACKED __attribute__((packed))
>  
>  typedef struct VhostUserMsg {
>      int request;



Acked-by: Michael S. Tsirkin <mst@redhat.com>

> -- 
> 2.39.5

Patchew 2.1-devel-b67e4c2

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