Re: [Qemu-devel] [PATCH] compiler: add a sizeof_field() macro

[John Snow]

On 06/14/2018 12:44 PM, Stefan Hajnoczi wrote:
> Determining the size of a field is useful when you don't have a struct
> variable handy.  Open-coding this is ugly.
> 
> This patch adds the sizeof_field() macro, which is similar to
> typeof_field().  Existing instances are updated to use the macro.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>

How'd you find all the existing instances?

Reviewed-by: John Snow <address@hidden>

> ---
>  include/hw/xen/io/ring.h      |  2 +-
>  include/qemu/compiler.h       |  2 ++
>  accel/tcg/translate-all.c     |  2 +-
>  hw/display/xenfb.c            |  4 ++--
>  hw/net/rocker/rocker_of_dpa.c |  2 +-
>  hw/net/virtio-net.c           |  2 +-
>  target/i386/kvm.c             |  2 +-
>  target/ppc/arch_dump.c        | 10 +++++-----
>  target/s390x/arch_dump.c      | 20 ++++++++++----------
>  9 files changed, 24 insertions(+), 22 deletions(-)
> 
> diff --git a/include/hw/xen/io/ring.h b/include/hw/xen/io/ring.h
> index abbca47687..ffa3ebadc8 100644
> --- a/include/hw/xen/io/ring.h
> +++ b/include/hw/xen/io/ring.h
> @@ -65,7 +65,7 @@ typedef unsigned int RING_IDX;
>   */
>  #define __CONST_RING_SIZE(_s, _sz) \
>      (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
> -         sizeof(((struct _s##_sring *)0)->ring[0])))
> +            sizeof_field(struct _s##_sring, ring[0])))
>  /*
>   * The same for passing in an actual pointer instead of a name tag.
>   */
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index 9f762695d1..5843812710 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -64,6 +64,8 @@
>          (type *) ((char *) __mptr - offsetof(type, member));})
>  #endif
>  
> +#define sizeof_field(type, field) sizeof(((type *)0)->field)
> +
>  /* Convert from a base type to a parent type, with compile time checking.  */
>  #ifdef __GNUC__
>  #define DO_UPCAST(type, field, dev) ( __extension__ ( { \
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index d48b56ca38..767066ecd6 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -132,7 +132,7 @@ typedef struct PageDesc {
>  
>  /* Make sure all possible CPU event bits fit in tb->trace_vcpu_dstate */
>  QEMU_BUILD_BUG_ON(CPU_TRACE_DSTATE_MAX_EVENTS >
> -                  sizeof(((TranslationBlock *)0)->trace_vcpu_dstate)
> +                  sizeof_field(TranslationBlock, trace_vcpu_dstate)
>                    * BITS_PER_BYTE);
>  
>  /*
> diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
> index f5afcc0358..911291c5c3 100644
> --- a/hw/display/xenfb.c
> +++ b/hw/display/xenfb.c
> @@ -525,8 +525,8 @@ static int xenfb_configure_fb(struct XenFB *xenfb, size_t 
> fb_len_lim,
>                                int width, int height, int depth,
>                                size_t fb_len, int offset, int row_stride)
>  {
> -    size_t mfn_sz = sizeof(*((struct xenfb_page *)0)->pd);
> -    size_t pd_len = sizeof(((struct xenfb_page *)0)->pd) / mfn_sz;
> +    size_t mfn_sz = sizeof_field(struct xenfb_page, pd[0]);
> +    size_t pd_len = sizeof_field(struct xenfb_page, pd) / mfn_sz;
>      size_t fb_pages = pd_len * XC_PAGE_SIZE / mfn_sz;
>      size_t fb_len_max = fb_pages * XC_PAGE_SIZE;
>      int max_width, max_height;
> diff --git a/hw/net/rocker/rocker_of_dpa.c b/hw/net/rocker/rocker_of_dpa.c
> index 60046720a5..8e347d1ee4 100644
> --- a/hw/net/rocker/rocker_of_dpa.c
> +++ b/hw/net/rocker/rocker_of_dpa.c
> @@ -104,7 +104,7 @@ typedef struct of_dpa_flow_key {
>  
>  /* Width of key which includes field 'f' in u64s, rounded up */
>  #define FLOW_KEY_WIDTH(f) \
> -    DIV_ROUND_UP(offsetof(OfDpaFlowKey, f) + sizeof(((OfDpaFlowKey *)0)->f), 
> \
> +    DIV_ROUND_UP(offsetof(OfDpaFlowKey, f) + sizeof_field(OfDpaFlowKey, f), \
>      sizeof(uint64_t))
>  
>  typedef struct of_dpa_flow_action {
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 90502fca7c..f154756e85 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -46,7 +46,7 @@
>   * 'container'.
>   */
>  #define endof(container, field) \
> -    (offsetof(container, field) + sizeof(((container *)0)->field))
> +    (offsetof(container, field) + sizeof_field(container, field))
>  
>  typedef struct VirtIOFeature {
>      uint64_t flags;
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 445e0e0b11..ad0e904b2c 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -1526,7 +1526,7 @@ static int kvm_put_fpu(X86CPU *cpu)
>  #define XSAVE_PKRU        672
>  
>  #define XSAVE_BYTE_OFFSET(word_offset) \
> -    ((word_offset) * sizeof(((struct kvm_xsave *)0)->region[0]))
> +    ((word_offset) * sizeof_field(struct kvm_xsave, region[0]))
>  
>  #define ASSERT_OFFSET(word_offset, field) \
>      QEMU_BUILD_BUG_ON(XSAVE_BYTE_OFFSET(word_offset) != \
> diff --git a/target/ppc/arch_dump.c b/target/ppc/arch_dump.c
> index 351a65b22f..cc1460e4e3 100644
> --- a/target/ppc/arch_dump.c
> +++ b/target/ppc/arch_dump.c
> @@ -210,11 +210,11 @@ static const struct NoteFuncDescStruct {
>      int contents_size;
>      void (*note_contents_func)(NoteFuncArg *arg, PowerPCCPU *cpu);
>  } note_func[] = {
> -    {sizeof(((Note *)0)->contents.prstatus),  ppc_write_elf_prstatus},
> -    {sizeof(((Note *)0)->contents.fpregset),  ppc_write_elf_fpregset},
> -    {sizeof(((Note *)0)->contents.vmxregset), ppc_write_elf_vmxregset},
> -    {sizeof(((Note *)0)->contents.vsxregset), ppc_write_elf_vsxregset},
> -    {sizeof(((Note *)0)->contents.speregset), ppc_write_elf_speregset},
> +    {sizeof_field(Note, contents.prstatus),  ppc_write_elf_prstatus},
> +    {sizeof_field(Note, contents.fpregset),  ppc_write_elf_fpregset},
> +    {sizeof_field(Note, contents.vmxregset), ppc_write_elf_vmxregset},
> +    {sizeof_field(Note, contents.vsxregset), ppc_write_elf_vsxregset},
> +    {sizeof_field(Note, contents.speregset), ppc_write_elf_speregset},
>      { 0, NULL}
>  };
>  
> diff --git a/target/s390x/arch_dump.c b/target/s390x/arch_dump.c
> index 6f61ff95af..c9ef0a6e60 100644
> --- a/target/s390x/arch_dump.c
> +++ b/target/s390x/arch_dump.c
> @@ -184,20 +184,20 @@ typedef struct NoteFuncDescStruct {
>  } NoteFuncDesc;
>  
>  static const NoteFuncDesc note_core[] = {
> -    {sizeof(((Note *)0)->contents.prstatus), s390x_write_elf64_prstatus},
> -    {sizeof(((Note *)0)->contents.fpregset), s390x_write_elf64_fpregset},
> +    {sizeof_field(Note, contents.prstatus), s390x_write_elf64_prstatus},
> +    {sizeof_field(Note, contents.fpregset), s390x_write_elf64_fpregset},
>      { 0, NULL}
>  };
>  
>  static const NoteFuncDesc note_linux[] = {
> -    {sizeof(((Note *)0)->contents.prefix),   s390x_write_elf64_prefix},
> -    {sizeof(((Note *)0)->contents.ctrs),     s390x_write_elf64_ctrs},
> -    {sizeof(((Note *)0)->contents.timer),    s390x_write_elf64_timer},
> -    {sizeof(((Note *)0)->contents.todcmp),   s390x_write_elf64_todcmp},
> -    {sizeof(((Note *)0)->contents.todpreg),  s390x_write_elf64_todpreg},
> -    {sizeof(((Note *)0)->contents.vregslo),  s390x_write_elf64_vregslo},
> -    {sizeof(((Note *)0)->contents.vregshi),  s390x_write_elf64_vregshi},
> -    {sizeof(((Note *)0)->contents.gscb),     s390x_write_elf64_gscb},
> +    {sizeof_field(Note, contents.prefix),   s390x_write_elf64_prefix},
> +    {sizeof_field(Note, contents.ctrs),     s390x_write_elf64_ctrs},
> +    {sizeof_field(Note, contents.timer),    s390x_write_elf64_timer},
> +    {sizeof_field(Note, contents.todcmp),   s390x_write_elf64_todcmp},
> +    {sizeof_field(Note, contents.todpreg),  s390x_write_elf64_todpreg},
> +    {sizeof_field(Note, contents.vregslo),  s390x_write_elf64_vregslo},
> +    {sizeof_field(Note, contents.vregshi),  s390x_write_elf64_vregshi},
> +    {sizeof_field(Note, contents.gscb),     s390x_write_elf64_gscb},
>      { 0, NULL}
>  };
>  
> 

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—js