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

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Message-Id: <20190712085908.4146364-1-arnd@arndb.de>
Date:   Fri, 12 Jul 2019 10:58:48 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Petr Mladek <pmladek@...e.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH] xen/trace: avoid clang warning on function pointers

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 <arnd@...db.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