On Thu, Oct 17, 2024 at 06:47:44PM +0100, 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.mer...@cloud.com>
>
> 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__)
>
Right! I actually tried put a (void)caml__frame to silence the
warning, but I didn't think of looking for a macro that would do
exactly that.
Do I have to resend the series with your patch, or can you commit it
directly?
Cheers,
Javi
