[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [XEN PATCH v1 2/3] ocaml/libs: Fill build failure due to unused variable in ocaml macro
On 17/10/2024 6:47 pm, Andrew Cooper wrote: > On 17/10/2024 5:20 pm, Javi Merino wrote: >> On Fedora 40, the build fails with: >> >> gcc -m64 -DBUILD_ID -fno-strict-aliasing -std=gnu99 -Wall >> -Wstrict-prototypes -Wno-unused-but-set-variable -Wno-unused-local-typedefs >> -Werror -O2 -fomit-frame-pointer >> -D__XEN_INTERFACE_VERSION__=__XEN_LATEST_INTERFACE_VERSION__ -MMD -MP -MF >> .domain_getinfo_stubs_v1.o.d -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE >> -fPIC -I/usr/lib64/ocaml -I >> /build/tools/ocaml/libs/xsd_glue/domain_getinfo_plugin_v1/../../../libs -I >> /build/tools/ocaml/libs/xsd_glue/domain_getinfo_plugin_v1/../../../libs/xsd_glue >> >> -I/build/tools/ocaml/libs/xsd_glue/domain_getinfo_plugin_v1/../../../../../tools/include >> -D__XEN_TOOLS__ >> -I/build/tools/ocaml/libs\/xsd_glue/domain_getinfo_plugin_v1/../../../../../tools/include >> -c -o domain_getinfo_stubs_v1.o domain_getinfo_stubs_v1.c >> In file included from domain_getinfo_stubs_v1.c:10: >> domain_getinfo_stubs_v1.c: In function 'xsd_glue_failwith': >> /usr/lib64/ocaml/caml/memory.h:275:29: error: unused variable >> 'caml__frame' [-Werror=unused-variable] >> 275 | struct caml__roots_block *caml__frame = *caml_local_roots_ptr >> | ^~~~~~~~~~~ >> domain_getinfo_stubs_v1.c:48:9: note: in expansion of macro 'CAMLparam0' >> 48 | CAMLparam0(); >> | ^~~~~~~~~~ >> cc1: all warnings being treated as errors >> >> The CAMLparam0 macro is defined in /usr/lib64/ocaml/caml/memory.h:255 as: >> >> #define CAMLparam0() \ >> struct caml__roots_block** caml_local_roots_ptr = \ >> (DO_CHECK_CAML_STATE ? Caml_check_caml_state() : (void)0, \ >> &CAML_LOCAL_ROOTS); \ >> struct caml__roots_block *caml__frame = *caml_local_roots_ptr >> >> We can't modify the macro. Mark the xsd_glue_failwith() function with >> ignore "-Wunused-variable" to prevent gcc from failing the build due >> to the unused variable. >> >> Fixes: a6576011a4d2 ("ocaml/libs: Implement a dynamically-loaded plugin for >> Xenctrl.domain_getinfo") >> Signed-off-by: Javi Merino <javi.merino@xxxxxxxxx> > That's horrible... > > I note the Ocaml manual even says: > > "Some C compilers give bogus warnings about unused variables > caml__dummy_xxx at each use of CAMLparam and CAMLlocal. You should > ignore them." which a brave claim to make... > > > The problem with pragma gcc is that we support Clang too. > > Having had a play, this works too > > @@ -45,7 +45,9 @@ static struct custom_operations xsd_glue_xenctrl_ops = { > static void Noreturn xsd_glue_failwith( > xc_interface *xch, const char *func, unsigned int line) > { > +#define caml__frame __attribute__((unused)) caml__frame > CAMLparam0(); > +#undef caml__frame > CAMLlocal1(msg); > const xc_error *error = xch ? xc_get_last_error(xch) : NULL; > char *str = NULL; > > and is rather more selective. > > > However, looking through other bits of memory.h, there's this gem: > > #define CAMLnoreturn ((void) caml__frame) > > which has existed since db3745919 "suppression des warnings "unused > variable" de gcc" in 2004. > > So, I think this is a better fix: > > @@ -69,6 +69,7 @@ static void Noreturn xsd_glue_failwith( > free(str); > > caml_raise_with_arg(*caml_named_value("xsg.error_v1"), msg); > + CAMLnoreturn; > } > #define xsd_glue_failwith(xch) xsd_glue_failwith(xch, __func__, __LINE__) > > and F40 seem happy with the result. And https://github.com/ocaml/ocaml/pull/13561 to update Ocaml's documentation on the matter. ~Andrew
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