On Wed, 2012-10-17 at 22:23 +0200, Arend van Spriel wrote: > 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 <srost...@redhat.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?
Yes. gcc 4.6.0 added a new option to gcc called '-mfentry'. The kernel build checks to see if this option is supported and if so it will use it. What this option does (when added to -pg), will not do the mcount calling but instead call fentry. The two have different semantics and are not compatible. When you built your kernel, the build process detected that -mfentry is supported and used that. Now when you built your modules with gcc 4.4.5, -mfentry was not supported and it used the mcount feature instead. In general, it's not a good idea to use two different gcc's to build the kernel and modules. But if you really need to, then you should disable function tracing of your modules, where the -pg and -mfentry wont be used. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
