[Qemu-devel] [PATCH v2] cpu_defs: Simplify CPUTLB padding logic

[Qemu-devel] [PATCH v2] cpu_defs: Simplify CPUTLB padding logic

[Peter Crosthwaite]

There was a complicated subtractive arithmetic for determining the
padding on the CPUTLBEntry structure. Simplify this with a union.

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
---
Changed since v1:
Remove un-needed anonymous union (Paolo review)
---
 include/exec/cpu-defs.h | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h
index 98b9cff..c6828cc 100644
--- a/include/exec/cpu-defs.h
+++ b/include/exec/cpu-defs.h
@@ -98,24 +98,23 @@ typedef uint64_t target_ulong;
 
 #define CPU_TLB_SIZE (1 << CPU_TLB_BITS)
 
-typedef struct CPUTLBEntry {
+typedef union CPUTLBEntry {
     /* bit TARGET_LONG_BITS to TARGET_PAGE_BITS : virtual address
        bit TARGET_PAGE_BITS-1..4  : Nonzero for accesses that should not
                                     go directly to ram.
        bit 3                      : indicates that the entry is invalid
        bit 2..0                   : zero
     */
-    target_ulong addr_read;
-    target_ulong addr_write;
-    target_ulong addr_code;
-    /* Addend to virtual address to get host address.  IO accesses
-       use the corresponding iotlb value.  */
-    uintptr_t addend;
+    struct {
+        target_ulong addr_read;
+        target_ulong addr_write;
+        target_ulong addr_code;
+        /* Addend to virtual address to get host address.  IO accesses
+           use the corresponding iotlb value.  */
+        uintptr_t addend;
+    };
     /* padding to get a power of two size */
-    uint8_t dummy[(1 << CPU_TLB_ENTRY_BITS) -
-                  (sizeof(target_ulong) * 3 +
-                   ((-sizeof(target_ulong) * 3) & (sizeof(uintptr_t) - 1)) +
-                   sizeof(uintptr_t))];
+    uint8_t dummy[1 << CPU_TLB_ENTRY_BITS];
 } CPUTLBEntry;
 
 QEMU_BUILD_BUG_ON(sizeof(CPUTLBEntry) != (1 << CPU_TLB_ENTRY_BITS));
-- 
1.9.1

Re: [Qemu-devel] [PATCH v2] cpu_defs: Simplify CPUTLB padding logic

[Richard Henderson]

On 07/09/2015 04:26 AM, Peter Crosthwaite wrote:
> There was a complicated subtractive arithmetic for determining the
> padding on the CPUTLBEntry structure. Simplify this with a union.
>
> Signed-off-by: Peter Crosthwaite<crosthwaite.peter@gmail.com>
> ---
> Changed since v1:
> Remove un-needed anonymous union (Paolo review)
> ---
>   include/exec/cpu-defs.h | 21 ++++++++++-----------
>   1 file changed, 10 insertions(+), 11 deletions(-)

Reviewed-by: Richard Henderson <rth@twiddle.net>


r~

Re: [Qemu-devel] [PATCH v2] cpu_defs: Simplify CPUTLB padding logic

[Paolo Bonzini]

On 09/07/2015 05:26, Peter Crosthwaite wrote:
> There was a complicated subtractive arithmetic for determining the
> padding on the CPUTLBEntry structure. Simplify this with a union.
> 
> Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
> ---
> Changed since v1:
> Remove un-needed anonymous union (Paolo review)
> ---
>  include/exec/cpu-defs.h | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h
> index 98b9cff..c6828cc 100644
> --- a/include/exec/cpu-defs.h
> +++ b/include/exec/cpu-defs.h
> @@ -98,24 +98,23 @@ typedef uint64_t target_ulong;
>  
>  #define CPU_TLB_SIZE (1 << CPU_TLB_BITS)
>  
> -typedef struct CPUTLBEntry {
> +typedef union CPUTLBEntry {
>      /* bit TARGET_LONG_BITS to TARGET_PAGE_BITS : virtual address
>         bit TARGET_PAGE_BITS-1..4  : Nonzero for accesses that should not
>                                      go directly to ram.
>         bit 3                      : indicates that the entry is invalid
>         bit 2..0                   : zero
>      */
> -    target_ulong addr_read;
> -    target_ulong addr_write;
> -    target_ulong addr_code;
> -    /* Addend to virtual address to get host address.  IO accesses
> -       use the corresponding iotlb value.  */
> -    uintptr_t addend;
> +    struct {
> +        target_ulong addr_read;
> +        target_ulong addr_write;
> +        target_ulong addr_code;
> +        /* Addend to virtual address to get host address.  IO accesses
> +           use the corresponding iotlb value.  */
> +        uintptr_t addend;
> +    };
>      /* padding to get a power of two size */
> -    uint8_t dummy[(1 << CPU_TLB_ENTRY_BITS) -
> -                  (sizeof(target_ulong) * 3 +
> -                   ((-sizeof(target_ulong) * 3) & (sizeof(uintptr_t) - 1)) +
> -                   sizeof(uintptr_t))];
> +    uint8_t dummy[1 << CPU_TLB_ENTRY_BITS];
>  } CPUTLBEntry;
>  
>  QEMU_BUILD_BUG_ON(sizeof(CPUTLBEntry) != (1 << CPU_TLB_ENTRY_BITS));
> 

Thanks, queued for 2.5.

Paolo