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Message-ID: <20190712174142.GB127917@archlinux-threadripper>
Date: Fri, 12 Jul 2019 10:41:42 -0700
From: Nathan Chancellor <natechancellor@...il.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
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: Re: [PATCH] xen/trace: avoid clang warning on function pointers
On Fri, Jul 12, 2019 at 10:58:48AM +0200, Arnd Bergmann wrote:
> 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>
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 <natechancellor@...il.com>
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