Re: [Libguestfs] [PATCH libnbd v3 2/6] generator: Add attribute((nonnull)) annotations to non-NULL parameters

On Thu, Sep 29, 2022 at 02:42:05PM +0100, Richard W.M. Jones wrote: > > > + (* Output __attribute__((nonnull)) for the function parameters: > > > + * eg. struct nbd_handle *, int, char * > > > + * => [ true, false, true ] > > > + * => LIBNBD_ATTRIBUTE_NONNULL((1,3)) > > > + * => __attribute__((nonnull,(1,3))) > > > > Style question. Do we want to REQUIRE the clients of this macro to > > pass in (), or would it be better to have a varargs format? > > > > > + *) > > > + let nns : bool list = > > > + [ true ] (* struct nbd_handle * *) > > > + @ List.flatten (List.map arg_attr_nonnull args) > > > + @ List.flatten (List.map optarg_attr_nonnull optargs) in > > > + let nns = List.mapi (fun i b -> (i+1, b)) nns in > > > + let nns = filter_map (fun (i, b) -> if b then Some i else None) nns in > > > + let nns : string list = List.map string_of_int nns in > > > + pr "\n LIBNBD_ATTRIBUTE_NONNULL((%s));\n" (String.concat "," nns) > > > > For generated code, it is just as easy to cope with either style (we > > can strip a layer of () if we want a varargs format). > > ... > > > + pr "#ifndef LIBNBD_ATTRIBUTE_NONNULL\n"; > > > + pr "#if defined(__GNUC__) && LIBNBD_GCC_VERSION >= 120000 /* gcc >= 12.0 */\n"; > > > + pr "#define LIBNBD_ATTRIBUTE_NONNULL(s) __attribute__((__nonnull__ s))\n"; > > > > This definition is what requires us to pass in our own (). That is, > > our end result is going to be one of: > > > > __attribute__((__nonnull__(1) )) > > __attribute__((__nonnull__(1, 2) )) > > > > but the difference is whether we must pass exactly one macro argument, > > and where that argument must include () even when there is only one > > parameter to be marked (what you coded): > > > > LIBNBD_ATTRIBUTE_NONNULL((1)) > > LIBNBD_ATTRIBUTE_NONNULL((1, 3)) > > > > vs. ease-of-use in supplying the () as part of the macro definition > > itself by using #define MACRO(...) and __VA_ARGS__: > > > > LIBNBD_ATTRIBUTE_NONNULL(1) > > LIBNBD_ATTRIBUTE_NONNULL(1, 3) > > I'm not sure I understand - what does the second definition look like? Using a shorter name for testing: $ cat foo.c #define my(...) __attribute__((__nonnull__(__VA_ARGS__))) extern void foo (char *a) my (1); extern void bar (char *a, char *b) my (1, 2); $ gcc -E foo.c # 0 "foo.c" # 0 "<built-in>" # 0 "<command-line>" # 1 "/usr/include/stdc-predef.h" 1 3 4 # 0 "<command-line>" 2 # 1 "foo.c" extern void foo (char *a) __attribute__((__nonnull__(1))); extern void bar (char *a, char *b) __attribute__((__nonnull__(1, 2))); $ gcc -o foo.o -c foo.c $ # compiled, so we satisfied gcc's attribute syntax and similarly, #define LIBNBD_ATTRIBUTE_NONNULL(...) /* no-op */ when disabling the macro.