coccinelle: new inplace-byteswaps.cocci to remove inplace-byteswapping calls

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: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Message-id: 20181009181612.10633-1-peter.maydell@linaro.org

scripts/coccinelle/inplace-byteswaps.cocci

+// 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);
+@@
+expression E;
+@@
+-be64_to_cpus(&E);
++E = be64_to_cpu(E);
+@@
+expression E;
+@@
+-cpu_to_be16s(&E);
++E = cpu_to_be16(E);
+@@
+expression E;
+@@
+-cpu_to_be32s(&E);
++E = cpu_to_be32(E);
+@@
+expression E;
+@@
+-cpu_to_be64s(&E);
++E = cpu_to_be64(E);
+@@
+expression E;
+@@
+-le16_to_cpus(&E);
++E = le16_to_cpu(E);
+@@
+expression E;
+@@
+-le32_to_cpus(&E);
++E = le32_to_cpu(E);
+@@
+expression E;
+@@
+-le64_to_cpus(&E);
++E = le64_to_cpu(E);
+@@
+expression E;
+@@
+-cpu_to_le16s(&E);
++E = cpu_to_le16(E);
+@@
+expression E;
+@@
+-cpu_to_le32s(&E);
++E = cpu_to_le32(E);
+@@
+expression E;
+@@
+-cpu_to_le64s(&E);
++E = cpu_to_le64(E);