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

[Peter Maydell]

On 9 October 2018 at 19:23, Eric Blake <address@hidden> wrote:
> 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 <address@hidden>
>> ---
>> 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:

This is kind of why I didn't post it as a patch to go in
scripts/ initially :-)  I suspected it was possible to
shorten it (maybe there's even coccinelle syntax to allow the
function names to be substituted to be specified with
a regex?), but the dumb-and-simple cut-and-paste for every
function being replaced worked and it didn't seem worth
spending even ten minutes messing around trying to improve
what is fundamentally a throwaway script...

thanks
-- PMM