linux-kernel - x86_64: undefined symbol 'mcount' in 3.7-rc1

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Message-ID: <507F13DE.2010601@broadcom.com>
Date:	Wed, 17 Oct 2012 22:23:58 +0200
From:	"Arend van Spriel" <arend@...adcom.com>
To:	linux-kernel@...r.kernel.org,
	"Steven Rostedt" <rostedt@...dmis.org>
Subject: x86_64: undefined symbol 'mcount' in 3.7-rc1

Hi Steven,

I have nightly test machines upgraded to 3.7-rc1 and on the 64-bit 
platform I get MODPOST warning on 'mcount'.

It is conditionally exported in x8664_ksyms_64.c:
#ifdef CONFIG_FUNCTION_TRACER
/* mcount is defined in assembly */
EXPORT_SYMBOL(mcount);
#endif

#ifdef CONFIG_FUNCTION_TRACER
#ifdef CC_USING_FENTRY
# define MCOUNT_ADDR           ((long)(__fentry__))
#else
# define MCOUNT_ADDR           ((long)(mcount))
#endif
#define MCOUNT_INSN_SIZE       5 /* sizeof mcount call */

I have built the kernel on x86 machine with gcc 4.6.3 and the modules 
are built during the test execution on test machine which has gcc 4.4.5. 
Reading commit below

commit d57c5d51a30152f3175d2344cb6395f08bf8ee0c
Author: Steven Rostedt <srostedt@...hat.com>
Date:   Wed Feb 9 13:32:18 2011 -0500

     ftrace/x86: Add support for -mfentry to x86_64

I suppose the gcc version mismatch is causing my problem. Is that a 
correct assumption?

Gr. AvS

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