Re: [PATCH v3 4/4] tools: add offsetof() to xen-tools/common-macros.h

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.03.2023 08:21, Juergen Gross wrote:
> --- a/tools/include/xen-tools/common-macros.h
> +++ b/tools/include/xen-tools/common-macros.h
> @@ -80,4 +80,8 @@
>      typeof( ((type *)0)->member ) *__mptr = (ptr);        \
>      (type *)( (char *)__mptr - offsetof(type,member) );})
>  
> +#ifndef offsetof
> +#define offsetof(a, b) __builtin_offsetof(a, b)
> +#endif

How's this going to work reliably with parties perhaps also including
stddef.h, which also is expected to define this macro, and which may
do so with a different sequence of tokens (even if that ends up
having the same effect)? There shouldn't be a need to define this
macro for any "normal" environments, e.g. ...

> --- a/tools/libfsimage/xfs/fsys_xfs.c
> +++ b/tools/libfsimage/xfs/fsys_xfs.c
> @@ -19,6 +19,7 @@
>  
>  #include <xenfsimage_grub.h>
>  #include "xfs.h"
> +#include <xen-tools/common-macros.h>
>  
>  #define MAX_LINK_COUNT       8
>  
> @@ -182,9 +183,6 @@ fsb2daddr (xfs_fsblock_t fsbno)
>                        (xfs_agblock_t)(fsbno & mask32lo(xfs.agblklog)));
>  }
>  
> -#undef offsetof
> -#define offsetof(t,m)        ((size_t)&(((t *)0)->m))
> -
>  static inline int
>  btroot_maxrecs (fsi_file_t *ffi)
>  {

... this library or ...

> --- a/tools/libs/vchan/init.c
> +++ b/tools/libs/vchan/init.c
> @@ -69,10 +69,6 @@
>  #define MAX_RING_SHIFT 20
>  #define MAX_RING_SIZE (1 << MAX_RING_SHIFT)
>  
> -#ifndef offsetof
> -#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
> -#endif
> -
>  static int init_gnt_srv(struct libxenvchan *ctrl, int domain)
>  {
>       int pages_left = ctrl->read.order >= PAGE_SHIFT ? 1 << 
> (ctrl->read.order - PAGE_SHIFT) : 0;

... this tool or ...

> --- a/tools/tests/vhpet/emul.h
> +++ b/tools/tests/vhpet/emul.h
> @@ -115,8 +115,6 @@ enum
>      NR_COMMON_SOFTIRQS
>  };
>  
> -#define offsetof(t, m) ((unsigned long )&((t *)0)->m)
> -
>  struct domain;
>  
>  struct vcpu

... this test binary (which is an ordinary host one as well). They all
should include stddef.h and be done.

Jan