Re: [Qemu-devel] [PATCH] coccinelle: new inplace-byteswaps.cocci to remove inplace-byteswapping calls

[Eric Blake <eblake@redhat.com>]

On 10/9/18 1:16 PM, Peter Maydell wrote:
> Add a new Coccinelle script which replaces uses of the inplace
> byteswapping functions *_to_cpus() and cpu_to_*s() with their
> not-in-place equivalents. This is useful for where the swapping
> is done on members of a packed struct -- taking the address
> of the member to pass it to an inplace function is undefined
> behaviour in C.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Richard asked for a coccinelle script in the scripts/coccinelle
> directory, so here's a patch to add it.
> 
>   scripts/coccinelle/inplace-byteswaps.cocci | 65 ++++++++++++++++++++++
>   1 file changed, 65 insertions(+)
>   create mode 100644 scripts/coccinelle/inplace-byteswaps.cocci
> 
> diff --git a/scripts/coccinelle/inplace-byteswaps.cocci b/scripts/coccinelle/inplace-byteswaps.cocci
> new file mode 100644
> index 00000000000..a869a90cbfd
> --- /dev/null
> +++ b/scripts/coccinelle/inplace-byteswaps.cocci
> @@ -0,0 +1,65 @@
> +// Replace uses of in-place byteswapping functions with calls to the
> +// equivalent not-in-place functions.  This is necessary to avoid
> +// undefined behaviour if the expression being swapped is a field in a
> +// packed struct.
> +
> +@@
> +expression E;
> +@@
> +-be16_to_cpus(&E);
> ++E = be16_to_cpu(E);
> +@@
> +expression E;
> +@@
> +-be32_to_cpus(&E);
> ++E = be32_to_cpu(E);

It's probably possible to shorten this as:

@@
expression E;
@@
(
-be16_to_cpus(&E);
+E = be16_to_cpu(E);
|
-be32_to_cpus(&E);
+E = be32_to_cpu(E);
...
)

But I'm also okay if the long form gets checked in.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org