Messages in this thread Patch in this message | | | Date | Tue, 6 Dec 2016 21:43:55 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH 4/7] arm: Add ftrace with regs support |
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On Tue, 6 Dec 2016 17:06:04 +0000 Abel Vesa <abelvesa@linux.com> wrote:
> This adds __ftrace_regs_caller which, unlike __ftrace_caller, > adds register saving/restoring and livepatch handling if > the pc register gets modified by klp_ftrace_handler. > > Signed-off-by: Abel Vesa <abelvesa@linux.com> > --- > arch/arm/kernel/entry-ftrace.S | 49 > ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 > insertions(+) > > diff --git a/arch/arm/kernel/entry-ftrace.S > b/arch/arm/kernel/entry-ftrace.S index c73c403..b6ada5c 100644 > --- a/arch/arm/kernel/entry-ftrace.S > +++ b/arch/arm/kernel/entry-ftrace.S > @@ -92,6 +92,46 @@ > 2: mcount_exit > .endm > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > + > +.macro __ftrace_regs_caller suffix > + > + stmdb sp!, {r0-r15} > + mov r3, sp > + > + ldr r10, [sp, #60] > + > + mcount_get_lr r1 @ lr of instrumented > func > + mcount_adjust_addr r0, lr @ > instrumented function + > + .globl ftrace_regs_call\suffix > +ftrace_regs_call\suffix: > + bl ftrace_stub > + > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER > + .globl ftrace_regs_graph_call\suffix > +ftrace_regs_graph_call\suffix: > + mov r0, r0 > +#endif
So basically what the below does is to undo the mcount prologue and recall the new function as the old function is called.
> +#ifdef CONFIG_LIVEPATCH > + ldr r0, [sp, #60] > + cmp r0, r10 > + beq ftrace_regs_caller_end > + ldmia sp!, {r0-r12} > + add sp, sp, #8 > + ldmia sp!, {r11} > + sub sp, r12, #16 > + str r11, [sp, #12] > + ldmia sp!, {r11, r12, lr, pc}
But the above really could do with a lot of comments to explain exactly what it is doing.
I don't condemn or condone this code. I'm just happy I don't have to maintain it.
-- Steve
> +#endif > +ftrace_regs_caller_end\suffix: > + ldmia sp!, {r0-r14} > + add sp, sp, #4 > + mov pc, lr > +.endm > + > +#endif > + > .macro __ftrace_caller suffix > mcount_enter > > @@ -212,6 +252,15 @@ UNWIND(.fnstart) > __ftrace_caller > UNWIND(.fnend) > ENDPROC(ftrace_caller) > + > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > +ENTRY(ftrace_regs_caller) > +UNWIND(.fnstart) > + __ftrace_regs_caller > +UNWIND(.fnend) > +ENDPROC(ftrace_regs_caller) > +#endif > + > #endif > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER
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