On 10/12/22, Martin Fernandez <martin.fernandez@xxxxxxxxxxxxx> wrote: > Add a description, an example and a couple of options when it is safe > to ignore it. > > Signed-off-by: Martin Fernandez <martin.fernandez@xxxxxxxxxxxxx> > --- > Documentation/dev-tools/checkpatch.rst | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/Documentation/dev-tools/checkpatch.rst > b/Documentation/dev-tools/checkpatch.rst > index c3389c6f3838..678c1956468b 100644 > --- a/Documentation/dev-tools/checkpatch.rst > +++ b/Documentation/dev-tools/checkpatch.rst > @@ -854,6 +854,32 @@ Macros, Attributes and Symbols > ... > } > > + **MACRO_ARG_REUSE** > + Using the same argument multiple times in the macro definition > + may lead to unwanted side effects. > + > + For example, given a min() macro defined like:: > + > + #define min(x, y) ((x) < (y) ? (x) : (y)) > + > + If you call it with ``min(foo(x), 0)``, it would expand to:: > + > + foo(x) < 0 ? foo(x) : 0 > + > + If foo has side effects or it's an expensive calculation the > + results might not be what the user intended. > + > + When it's safe to ignore: > + > + - If the macro arguments of all uses of this macro are free of > + unintended side effects. Passing a constant value is usually > + fine, as the compiler will use constant propagation and further > + optimizations to produce acceptable code. > + > + - If you defined local variables that will hold the value of each > + argument in the macro's definition. See the min() macro in > + include/linux/minmax.h for example. > + > **MISPLACED_INIT** > It is possible to use section markers on variables in a way > which gcc doesn't understand (or at least not the way the > -- > 2.30.2 > > Sending it again since I've got no response
