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From: Steven Rostedt <>
To: Bjorn Helgaas <>
Cc: Frederic Weisbecker <>,
	Ingo Molnar <>,
	"" <>,
	Lance Ortiz <>, Gary Hade <>
Subject: Re: "unsigned expression < 0" always false warning
Date: Fri, 19 Apr 2013 17:17:42 -0400
Message-ID: <1366406262.9609.123.camel@gandalf.local.home> (raw)
In-Reply-To: <>

Does this fix your issue?

-- Steve

>From d2802d0739dcc61af5e5ea00773ce7ddead4e9c2 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <>
Date: Fri, 19 Apr 2013 17:10:27 -0400
Subject: [PATCH] tracing: Compare to 1 instead of zero for is_signed_type()

The formats of the trace events show if the type of a event field
is signed or not via a macro called is_signed_type(). This does
a trick with the type and compares a -1 to zero after typecasting
to the tested type. If it returns true, it's signed, otherwise
its not. But this unfortunately triggers a warning by gcc:

  warning: comparison of unsigned expression < 0 is always false

As we know it is always false (that's why we do it), this is a
false warning. Luckily for us, the comparison works with a 1 as
well, without giving the warning.

Convert the check to compare (type)-1 < (type)0 to (type)-1 < (type)1
to determine if the type is signed or not.


Reported-by: Bjorn Helgaas <>
Reported-by: Gary Hade <>
Signed-off-by: Steven Rostedt <>
 include/linux/ftrace_event.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4e28b01..34e00fb 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -333,7 +333,7 @@ extern int trace_define_field(struct ftrace_event_call *call, const char *type,
 extern int trace_add_event_call(struct ftrace_event_call *call);
 extern void trace_remove_event_call(struct ftrace_event_call *call);
-#define is_signed_type(type)	(((type)(-1)) < (type)0)
+#define is_signed_type(type)	(((type)(-1)) < (type)1)
 int trace_set_clr_event(const char *system, const char *event, int set);

  parent reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-15 17:17 Bjorn Helgaas
2013-04-19 20:43 ` Gary Hade
2013-04-19 21:05   ` Steven Rostedt
2013-04-19 21:17 ` Steven Rostedt [this message]
2013-04-19 22:30   ` Bjorn Helgaas
2013-04-19 22:45     ` Gary Hade

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