On Wed, 15 Mar 2017 15:55:32 -0400 Steven Rostedt <[email protected]> wrote:
> From: "Steven Rostedt (VMware)" <[email protected]> > > x86_64 has had fentry support for some time. I did not add support to x86_32 > as I was unsure if it will be used much in the future. It is still very much > used, and there's issues with function graph tracing with gcc playing around > with the mcount frames, causing function graph to panic. The fentry code > does not have this issue, and is able to cope as there is no frame to mess > up. > > Note, this only add support for fentry when DYNAMIC_FTRACE is set. There's > really no reason to not have that set, because the performance of the > machine drops significantly when it's not enabled. I only keep > !DYNAMIC_FTRACE around to test it off, as there's still some archs that have > FTRACE but not DYNAMIC_FTRACE. > > Signed-off-by: Steven Rostedt (VMware) <[email protected]> > --- > arch/x86/Kconfig | 2 +- > arch/x86/kernel/ftrace_32.S | 88 > +++++++++++++++++++++++++++++++++++++++------ > 2 files changed, 79 insertions(+), 11 deletions(-) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index cc98d5a294ee..8c17146427ca 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -127,7 +127,7 @@ config X86 > select HAVE_EBPF_JIT if X86_64 > select HAVE_EFFICIENT_UNALIGNED_ACCESS > select HAVE_EXIT_THREAD > - select HAVE_FENTRY if X86_64 > + select HAVE_FENTRY if X86_64 || DYNAMIC_FTRACE > select HAVE_FTRACE_MCOUNT_RECORD > select HAVE_FUNCTION_GRAPH_TRACER > select HAVE_FUNCTION_TRACER > diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S > index 8ca33d9806ac..4bf8223555cd 100644 > --- a/arch/x86/kernel/ftrace_32.S > +++ b/arch/x86/kernel/ftrace_32.S > @@ -9,27 +9,75 @@ > #include <asm/export.h> > #include <asm/ftrace.h> > > + > +#ifdef CC_USING_FENTRY > +# define function_hook __fentry__ > +EXPORT_SYMBOL(__fentry__) > +#else > +# define function_hook mcount > +EXPORT_SYMBOL(mcount) > +#endif > + > +/* mcount uses a frame pointer even if CONFIG_FRAME_POINTER is not set */ > +#if !defined(CC_USING_FENTRY) || defined(CONFIG_FRAME_POINTER) > +# define USING_FRAME_POINTER > +#endif > + > +#ifdef USING_FRAME_POINTER > +# ifdef CC_USING_FENTRY > +# define MCOUNT_FRAME_SIZE (4*4) /* bp,ip and parent's */ > +# else > +# define MCOUNT_FRAME_SIZE 4 /* just the bp */ > +# endif > +# define MCOUNT_FRAME 1 /* using frame = true > */ > +#else > +# define MCOUNT_FRAME_SIZE 0 /* no stack frame */ > +# define MCOUNT_FRAME 0 /* using frame = false > */ > +#endif It seems that there is no use of MCOUNT_FRAME_SIZE below. Do we really need it? Thanks, -- Masami Hiramatsu <[email protected]>
