On Thu 2016-12-08 22:46:55, Abel Vesa wrote: > On Thu, Dec 08, 2016 at 09:46:35PM +0000, Abel Vesa wrote: > > From: Jean-Jacques Hiblot <jjhib...@traphandler.com> > > > > From: Jean-Jacques Hiblot <jjhib...@traphandler.com> > > >From statement twice in the commit message. Will resend. > > > > The DYNAMIC_FTRACE_WITH_REGS configuration makes it possible for a ftrace > > operation to specify if registers need to saved/restored by the ftrace > > handler. > > This is needed by kgraft and possibly other ftrace-based tools, and the ARM > > architecture is currently lacking this feature. It would also be the first > > step > > to support the "Kprobes-on-ftrace" optimization on ARM. > > > > This patch introduces a new ftrace handler that stores the registers on the > > stack before calling the next stage. The registers are restored from the > > stack > > before going back to the instrumented function. > > > > A side-effect of this patch is to activate the support for > > ftrace_modify_call() > > as it defines ARCH_SUPPORTS_FTRACE_OPS for the ARM architecture > > > > Signed-off-by: Jean-Jacques Hiblot <jjhib...@traphandler.com> > > Signed-off-by: Abel Vesa <abelv...@linux.com> > > --- > > arch/arm/Kconfig | 2 ++ > > arch/arm/include/asm/ftrace.h | 4 +++ > > arch/arm/kernel/entry-ftrace.S | 78 > > ++++++++++++++++++++++++++++++++++++++++++ > > arch/arm/kernel/ftrace.c | 33 ++++++++++++++++++ > > 4 files changed, 117 insertions(+) > > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > > index b5d529f..87f1a9f 100644 > > --- a/arch/arm/Kconfig > > +++ b/arch/arm/Kconfig > > @@ -50,6 +50,7 @@ config ARM > > select HAVE_DMA_API_DEBUG > > select HAVE_DMA_CONTIGUOUS if MMU > > select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU > > + select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE > > select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) > > && MMU > > select HAVE_EXIT_THREAD > > select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL) > > @@ -90,6 +91,7 @@ config ARM > > select PERF_USE_VMALLOC > > select RTC_LIB > > select SYS_SUPPORTS_APM_EMULATION > > + select FRAME_POINTER if DYNAMIC_FTRACE_WITH_REGS && > > FUNCTION_GRAPH_TRACER
FRAME_POINTER is not for free. It takes space on the stack. Also there is a performance penalty. Do we really need to depend on it? If so, it might be worth a note in the commit message. I made only a quick look at the patch. It looks reasonable. But I do not have enough knowledge about the arm architecture, assembly, and ftrace-specifics. Also I cannot test it easily. So issues might be hidden to my eyes. Best Regards, Petr
