[PATCH] xen/trace: avoid clang warning on function pointers

[Arnd Bergmann]

clang-9 does not like the way that the is_signed_type() compares
function pointers deep inside of the trace even macros:

In file included from arch/x86/xen/trace.c:21:
In file included from include/trace/events/xen.h:475:
In file included from include/trace/define_trace.h:102:
In file included from include/trace/trace_events.h:467:
include/trace/events/xen.h:69:7: error: ordered comparison of function pointers ('xen_mc_callback_fn_t' (aka 'void (*)(void *)') and 'xen_mc_callback_fn_t') [-Werror,-Wordered-compare-function-pointers]
__field(xen_mc_callback_fn_t, fn)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/trace/trace_events.h:415:29: note: expanded from macro '__field'
#define __field(type, item) __field_ext(type, item, FILTER_OTHER)
^
include/trace/trace_events.h:401:6: note: expanded from macro '__field_ext'
is_signed_type(type), filter_type); \
^
include/linux/trace_events.h:540:44: note: expanded from macro 'is_signed_type'
#define is_signed_type(type) (((type)(-1)) < (type)1)
^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
include/trace/trace_events.h:77:16: note: expanded from macro 'TRACE_EVENT'
PARAMS(tstruct), \
~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/tracepoint.h:95:25: note: expanded from macro 'PARAMS'
#define PARAMS(args...) args
^
include/trace/trace_events.h:455:2: note: expanded from macro 'DECLARE_EVENT_CLASS'
tstruct; \
^~~~~~~

I guess the warning is reasonable in principle, though this seems to
be the only instance we get in the entire kernel today.
Shut up the warning by making it a void pointer in the exported
structure.

Fixes: c796f213a693 ("xen/trace: add multicall tracing")
Signed-off-by: Arnd Bergmann <ar...@arndb.de>
---
include/trace/events/xen.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/trace/events/xen.h b/include/trace/events/xen.h
index 9a0e8af21310..f75b77414ac1 100644
--- a/include/trace/events/xen.h
+++ b/include/trace/events/xen.h
@@ -66,7 +66,7 @@ TRACE_EVENT(xen_mc_callback,
TP_PROTO(xen_mc_callback_fn_t fn, void *data),
TP_ARGS(fn, data),
TP_STRUCT__entry(
- __field(xen_mc_callback_fn_t, fn)
+ __field(void *, fn)
__field(void *, data)
),
TP_fast_assign(
--
2.20.0

[Sedat Dilek]

Thanks for bringing this up (again), Arnd.

As this is a known CBL issue please add...

Link: https://github.com/ClangBuiltLinux/linux/issues/97

...and...

Tested-by: Sedat Dilek <sedat...@gmail.com>

For the sake of completeness see also the comments of Steven Rostedt
and user "Honeybyte" in the above Link - if not known/read.

- Sedat -

P.S.: I am using this patch since 6 months in my
for-5.x/clang-warningfree local Git repository.

> Fixes: c796f213a693 ("xen/trace: add multicall tracing")
> Signed-off-by: Arnd Bergmann <ar...@arndb.de>
> ---
> include/trace/events/xen.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/trace/events/xen.h b/include/trace/events/xen.h
> index 9a0e8af21310..f75b77414ac1 100644
> --- a/include/trace/events/xen.h
> +++ b/include/trace/events/xen.h
> @@ -66,7 +66,7 @@ TRACE_EVENT(xen_mc_callback,
> TP_PROTO(xen_mc_callback_fn_t fn, void *data),
> TP_ARGS(fn, data),
> TP_STRUCT__entry(
> - __field(xen_mc_callback_fn_t, fn)
> + __field(void *, fn)
> __field(void *, data)
> ),
> TP_fast_assign(
> --
> 2.20.0
>

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[Nathan Chancellor]

Nick suggested this as well, I think it's reasonable to work around it
in this one location since this is indeed the only instance of this
warning that I see in the kernel tree across all of my builds.

Reviewed-by: Nathan Chancellor <natecha...@gmail.com>

[Nick Desaulniers]

Steven, Ingo, would one of you mind picking up this fix, please? See
for multiple reports:
https://github.com/ClangBuiltLinux/linux/issues/216
--
Thanks,
~Nick Desaulniers

[Nick Desaulniers]

On Mon, Sep 23, 2019 at 3:06 PM Nick Desaulniers
<ndesau...@google.com> wrote:
> Steven, Ingo, would one of you mind picking up this fix, please? See
> for multiple reports:
> https://github.com/ClangBuiltLinux/linux/issues/216

Sorry, https://github.com/ClangBuiltLinux/linux/issues/97 is the link.
--
Thanks,
~Nick Desaulniers