Messages in this thread Patch in this message | | | From | Jean-Jacques Hiblot <> | Date | Thu, 12 Jan 2017 15:30:44 +0100 | Subject | Re: [PATCH] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS |
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2017-01-12 1:19 GMT+01:00 Abel Vesa <abelvesa@gmail.com>: > On Tue, Jan 10, 2017 at 04:51:12PM +0100, Petr Mladek wrote: >> 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 <jjhiblot@traphandler.com> >> > > >> > > From: Jean-Jacques Hiblot <jjhiblot@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 <jjhiblot@traphandler.com> >> > > Signed-off-by: Abel Vesa <abelvesa@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 > Hi Petr, >> >> 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. >
FRAME_POINTER is not needed. the dependency is wrong and should be removed. The code must be modified to not use fp register:
--- a/arch/arm/kernel/entry-ftrace.S +++ b/arch/arm/kernel/entry-ftrace.S @@ -130,7 +130,8 @@ ftrace_graph_regs_call: #ifdef CONFIG_FUNCTION_GRAPH_TRACER .macro __ftrace_graph_regs_caller
- sub r0, fp, #4 @ lr of instrumented routine (parent) + add r0, sp, #64 @ r0 is now a pointer to lr of + @ instrumented routine
@ called from __ftrace_regs_caller ldr r1, [sp, #56] @ instrumented routine (func) @@ -139,8 +140,9 @@ ftrace_graph_regs_call: mov r2, fp @ frame pointer bl prepare_ftrace_return
- ldr lr, [fp, #-4] @ restore lr from the stack - ldmia sp, {r0-r11, ip, sp} @ restore r0 through sp + ldr lr, [sp, #64] @ get the previous LR value from stack + ldmia sp, {r0-r11, ip, sp} @ pop the saved registers INCLUDING + @ the stack pointer ret ip .endm #endif
Jean-Jacques
> I was trying to create my own patch when I found this work done by > Jean-Jacques, so I haven't looked specifically for the FRAME_POINTER > part. I looked now at it and you seem to be right, FRAME_POINTER is > not needed. > > I will get rid of the FRAME_POINTER part, change the authorship and > send it again in the following days. >> >> 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 > Thanks, > Abel
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