Re: [Xen-devel] [PATCH 1/2] cpu_ioreq_pio, cpu_ioreq_move: introduce read_phys_req_item, write_phys_req_item

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 10 Dec 2012, Ian Jackson wrote:
> Replace a lot of formulaic multiplications (containing casts, no less)
> with calls to a pair of functions.  This encapsulates in a single
> place the operations which require care relating to integer overflow.
> 
> Cc: Dongxiao Xu <dongxiao.xu@xxxxxxxxx>
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> ---
>  xen-all.c |   73 
> ++++++++++++++++++++++++++++++++++++-------------------------
>  1 files changed, 43 insertions(+), 30 deletions(-)
> 
> diff --git a/xen-all.c b/xen-all.c
> index 046cc2a..97c8ef4 100644
> --- a/xen-all.c
> +++ b/xen-all.c
> @@ -682,11 +682,42 @@ static void do_outp(pio_addr_t addr,
>      }
>  }
>  
> -static void cpu_ioreq_pio(ioreq_t *req)
> +/*
> + * Helper functions which read/write an object from/to physical guest
> + * memory, as part of the implementation of an ioreq.
> + *
> + * Equivalent to
> + *   cpu_physical_memory_rw(addr + (req->df ? -1 : +1) * req->size * i,
> + *                          val, req->size, 0/1)
> + * except without the integer overflow problems.
> + */
> +static void rw_phys_req_item(hwaddr addr,
> +                             ioreq_t *req, uint32_t i, void *val, int rw)
> +{
> +    /* Do everything unsigned so overflow just results in a truncated result
> +     * and accesses to undesired parts of guest memory, which is up
> +     * to the guest */
> +    hwaddr offset = (hwaddr)req->size * i;
> +    if (req->df) addr -= offset;
> +    else addr += offset;
> +    cpu_physical_memory_rw(addr, val, req->size, rw);
> +}

QEMU's code style is

if (something) {

you can also run the patch through scripts/checkpatch.pl.

Aside from the code style issue:

Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


> +static inline void read_phys_req_item(hwaddr addr,
> +                                      ioreq_t *req, uint32_t i, void *val)
> +{
> +    rw_phys_req_item(addr, req, i, val, 0);
> +}
> +static inline void write_phys_req_item(hwaddr addr,
> +                                       ioreq_t *req, uint32_t i, void *val)
>  {
> -    int i, sign;
> +    rw_phys_req_item(addr, req, i, val, 1);
> +}
>  
> -    sign = req->df ? -1 : 1;
> +
> +static void cpu_ioreq_pio(ioreq_t *req)
> +{
> +    int i;
>  
>      if (req->dir == IOREQ_READ) {
>          if (!req->data_is_ptr) {
> @@ -696,9 +727,7 @@ static void cpu_ioreq_pio(ioreq_t *req)
>  
>              for (i = 0; i < req->count; i++) {
>                  tmp = do_inp(req->addr, req->size);
> -                cpu_physical_memory_write(
> -                        req->data + (sign * i * (int64_t)req->size),
> -                        (uint8_t *) &tmp, req->size);
> +                write_phys_req_item(req->data, req, i, &tmp);
>              }
>          }
>      } else if (req->dir == IOREQ_WRITE) {
> @@ -708,9 +737,7 @@ static void cpu_ioreq_pio(ioreq_t *req)
>              for (i = 0; i < req->count; i++) {
>                  uint32_t tmp = 0;
>  
> -                cpu_physical_memory_read(
> -                        req->data + (sign * i * (int64_t)req->size),
> -                        (uint8_t*) &tmp, req->size);
> +                read_phys_req_item(req->data, req, i, &tmp);
>                  do_outp(req->addr, req->size, tmp);
>              }
>          }
> @@ -719,22 +746,16 @@ static void cpu_ioreq_pio(ioreq_t *req)
>  
>  static void cpu_ioreq_move(ioreq_t *req)
>  {
> -    int i, sign;
> -
> -    sign = req->df ? -1 : 1;
> +    int i;
>  
>      if (!req->data_is_ptr) {
>          if (req->dir == IOREQ_READ) {
>              for (i = 0; i < req->count; i++) {
> -                cpu_physical_memory_read(
> -                        req->addr + (sign * i * (int64_t)req->size),
> -                        (uint8_t *) &req->data, req->size);
> +                read_phys_req_item(req->addr, req, i, &req->data);
>              }
>          } else if (req->dir == IOREQ_WRITE) {
>              for (i = 0; i < req->count; i++) {
> -                cpu_physical_memory_write(
> -                        req->addr + (sign * i * (int64_t)req->size),
> -                        (uint8_t *) &req->data, req->size);
> +                write_phys_req_item(req->addr, req, i, &req->data);
>              }
>          }
>      } else {
> @@ -742,21 +763,13 @@ static void cpu_ioreq_move(ioreq_t *req)
>  
>          if (req->dir == IOREQ_READ) {
>              for (i = 0; i < req->count; i++) {
> -                cpu_physical_memory_read(
> -                        req->addr + (sign * i * (int64_t)req->size),
> -                        (uint8_t*) &tmp, req->size);
> -                cpu_physical_memory_write(
> -                        req->data + (sign * i * (int64_t)req->size),
> -                        (uint8_t*) &tmp, req->size);
> +                read_phys_req_item(req->addr, req, i, &tmp);
> +                write_phys_req_item(req->data, req, i, &tmp);
>              }
>          } else if (req->dir == IOREQ_WRITE) {
>              for (i = 0; i < req->count; i++) {
> -                cpu_physical_memory_read(
> -                        req->data + (sign * i * (int64_t)req->size),
> -                        (uint8_t*) &tmp, req->size);
> -                cpu_physical_memory_write(
> -                        req->addr + (sign * i * (int64_t)req->size),
> -                        (uint8_t*) &tmp, req->size);
> +                read_phys_req_item(req->data, req, i, &tmp);
> +                write_phys_req_item(req->addr, req, i, &tmp);
>              }
>          }
>      }
> -- 
> 1.7.2.5
> 

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