Re: [PATCHv2] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS

Jean-Jacques Hiblot
2017-02-10T16:25:28Z

2017-02-07 20:18 GMT+01:00 Abel Vesa <abelvesa@gmail.com>:
> On Wed, Jan 25, 2017 at 07:30:32PM +0100, Jean-Jacques Hiblot wrote:
>
>> Abel, I tested it partially.
>
> OK, so I managed to find exactly what is happening.
>
>> It's seems OK if I have FRAME_POINTER enabled and it breaks otherwise.
>
> FRAME_POINTER is needed by OLD_MCOUNT.
>
> OLD_MCOUNT is needed by __ftrace_modify_code in order to be able to do set_kernel_text_rw.
> (The other implementation does not allow writing to kernel text therefore the warning
> happens)

That seems strange. It shouldn't make a difference whether the
old_mcount is enabled or not, we need to be able to modify the code.
IMO the ARM implementation of __ftrace_modify_code() and
arch_ftrace_update_code() must not be excluded when CONFIG_OLD_MCOUNT
is not defined.

>
> If you try the same thing without the patch you will get an "Invalid argument" at
> module loading.
>
>>
>> My test case attaches a tracing handler to a function "myfunc":
>>
>> static struct ftrace_ops kprobe_ftrace_ops __read_mostly = {
>> .func = jjh_ftrace_handler,
>> .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC,
>> };
>>
>> ftrace_set_filter(&kprobe_ftrace_ops, "myfunc", 4, 0);
>> register_ftrace_function(&kprobe_ftrace_ops);
>>
>> I won't send the actual code because it's too messy. If you need help
>> to reproduce, I'll try to extract the relevant part.
>>
>> Before the crash I observe the following warning.
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 9 at kernel/trace/ftrace.c:2526
>> ftrace_modify_all_code+0xd8/0x158
>> Modules linked in: jjh_test(+)
>> CPU: 0 PID: 9 Comm: migration/0 Tainted: G W 4.7.0+ #53
>> Hardware name: ARM-Versatile Express
>> [<8010f7bc>] (unwind_backtrace) from [<8010b6f8>] (show_stack+0x18/0x1c)
>> [<8010b6f8>] (show_stack) from [<803a1548>] (dump_stack+0x80/0xa0)
>> [<803a1548>] (dump_stack) from [<8011ef20>] (__warn+0xe0/0x10c)
>> [<8011ef20>] (__warn) from [<8011ef74>] (warn_slowpath_null+0x28/0x30)
>> [<8011ef74>] (warn_slowpath_null) from [<8019d2a4>]
>> (ftrace_modify_all_code+0xd8/0x158)
>> [<8019d2a4>] (ftrace_modify_all_code) from [<8019d330>]
>> (__ftrace_modify_code+0xc/0x14)
>> [<8019d330>] (__ftrace_modify_code) from [<80198908>]
>> (multi_cpu_stop+0xe8/0x114)
>> [<80198908>] (multi_cpu_stop) from [<80198588>] (cpu_stopper_thread+0x60/0x134)
>> [<80198588>] (cpu_stopper_thread) from [<8013f428>]
>> (smpboot_thread_fn+0x148/0x1c4)
>> [<8013f428>] (smpboot_thread_fn) from [<8013c00c>] (kthread+0xe0/0xfc)
>> [<8013c00c>] (kthread) from [<80107db8>] (ret_from_fork+0x14/0x3c)
>> ---[ end trace f7d50cc2a4627fb1 ]---
>>
>> Jean-Jacques
>>
>>
>>
>>
>> 2017-01-25 0:24 GMT+01:00 Abel Vesa <abelvesa@linux.com>:
>> > 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: Abel Vesa <abelvesa@linux.com>
>> > ---
>> > arch/arm/Kconfig | 1 +
>> > arch/arm/include/asm/ftrace.h | 4 +++
>> > arch/arm/kernel/entry-ftrace.S | 79 ++++++++++++++++++++++++++++++++++++++++++
>> > arch/arm/kernel/ftrace.c | 33 ++++++++++++++++++
>> > 4 files changed, 117 insertions(+)
>> >
>> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> > index 186c4c2..db40973 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
>
> The solution is to replace this:
>> > + select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> with this:
> + select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE && OLD_MCOUNT
>
>> > 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)
>> > diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
>> > index 22b7311..f379881 100644
>> > --- a/arch/arm/include/asm/ftrace.h
>> > +++ b/arch/arm/include/asm/ftrace.h
>> > @@ -1,6 +1,10 @@
>> > #ifndef _ASM_ARM_FTRACE
>> > #define _ASM_ARM_FTRACE
>> >
>> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> > +#define ARCH_SUPPORTS_FTRACE_OPS 1
>> > +#endif
>> > +
>> > #ifdef CONFIG_FUNCTION_TRACER
>> > #define MCOUNT_ADDR ((unsigned long)(__gnu_mcount_nc))
>> > #define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
>> > diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
>> > index c73c403..fcdcc3a 100644
>> > --- a/arch/arm/kernel/entry-ftrace.S
>> > +++ b/arch/arm/kernel/entry-ftrace.S
>> > @@ -92,12 +92,74 @@
>> > 2: mcount_exit
>> > .endm
>> >
>> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> > +
>> > +.macro __ftrace_regs_caller
>> > +
>> > + add ip, sp, #4 @ move in IP the value of SP as it was
>> > + @ before the push {lr} of the mcount mechanism
>> > + stmdb sp!, {ip,lr,pc}
>> > + stmdb sp!, {r0-r11,lr}
>> > +
>> > + @ stack content at this point:
>> > + @ 0 4 44 48 52 56 60 64
>> > + @ RO | R1 | ... | R11 | LR | SP + 4 | LR | PC | previous LR |
>> > +
>> > + mov r3, sp @ struct pt_regs*
>> > + ldr r2, =function_trace_op
>> > + ldr r2, [r2] @ pointer to the current
>> > + @ function tracing op
>> > + ldr r1, [sp, #64] @ lr of instrumented func
>> > + mcount_adjust_addr r0, lr @ instrumented function
>> > +
>> > + .globl ftrace_regs_call
>> > +ftrace_regs_call:
>> > + bl ftrace_stub
>> > +
>> > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>> > + .globl ftrace_graph_regs_call
>> > +ftrace_graph_regs_call:
>> > + mov r0, r0
>> > +#endif
>> > + 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
>> > +
>> > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>> > +.macro __ftrace_graph_regs_caller
>> > +
>> > + sub r0, fp, #4 @ lr of instrumented routine (parent)
>> > +
>> > + @ called from __ftrace_regs_caller
>> > + ldr r1, [sp, #56] @ instrumented routine (func)
>> > + mcount_adjust_addr r1, r1
>> > +
>> > + sub r2, r0, #4 @ frame pointer
>> > + bl prepare_ftrace_return
>> > +
>> > + ldr lr, [sp, #64] @ restore lr from the stack
>> > + ldmia sp, {r0-r11, ip, sp} @ restore r0 through sp
>> > + ret ip
>> > +
>> > +.endm
>> > +#endif
>> > +#endif
>> > +
>> > .macro __ftrace_caller suffix
>> > mcount_enter
>> >
>> > mcount_get_lr r1 @ lr of instrumented func
>> > mcount_adjust_addr r0, lr @ instrumented function
>> >
>> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> > + ldr r2, =function_trace_op
>> > + ldr r2, [r2] @ pointer to the current
>> > + @ function tracing op
>> > + mov r3, #0 @ regs is NULL
>> > +#endif
>> > +
>> > .globl ftrace_call\suffix
>> > ftrace_call\suffix:
>> > bl ftrace_stub
>> > @@ -212,6 +274,15 @@ 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
>> > @@ -220,6 +291,14 @@ UNWIND(.fnstart)
>> > __ftrace_graph_caller
>> > UNWIND(.fnend)
>> > ENDPROC(ftrace_graph_caller)
>> > +
>> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> > +ENTRY(ftrace_graph_regs_caller)
>> > +UNWIND(.fnstart)
>> > + __ftrace_graph_regs_caller
>> > +UNWIND(.fnend)
>> > +ENDPROC(ftrace_graph_regs_caller)
>> > +#endif
>> > #endif
>> >
>> > .purgem mcount_enter
>> > diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
>> > index 3f17594..d8d4753 100644
>> > --- a/arch/arm/kernel/ftrace.c
>> > +++ b/arch/arm/kernel/ftrace.c
>> > @@ -139,6 +139,15 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
>> >
>> > ret = ftrace_modify_code(pc, 0, new, false);
>> >
>> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> > + if (!ret) {
>> > + pc = (unsigned long)&ftrace_regs_call;
>> > + new = ftrace_call_replace(pc, (unsigned long)func);
>> > +
>> > + ret = ftrace_modify_code(pc, 0, new, false);
>> > + }
>> > +#endif
>> > +
>> > #ifdef CONFIG_OLD_MCOUNT
>> > if (!ret) {
>> > pc = (unsigned long)&ftrace_call_old;
>> > @@ -157,6 +166,20 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>> > unsigned long ip = rec->ip;
>> >
>> > old = ftrace_nop_replace(rec);
>> > +
>> > + new = ftrace_call_replace(ip, adjust_address(rec, addr));
>> > +
>> > + return ftrace_modify_code(rec->ip, old, new, true);
>> > +}
>> > +
>
> Also this function implementation needs to be in an #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS clause:
>
>> > +int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
>> > + unsigned long addr)
>> > +{
>> > + unsigned long new, old;
>> > + unsigned long ip = rec->ip;
>> > +
>> > + old = ftrace_call_replace(ip, adjust_address(rec, old_addr));
>> > +
>> > new = ftrace_call_replace(ip, adjust_address(rec, addr));
>> >
>> > return ftrace_modify_code(rec->ip, old, new, true);
>> > @@ -229,6 +252,8 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
>> > extern unsigned long ftrace_graph_call;
>> > extern unsigned long ftrace_graph_call_old;
>> > extern void ftrace_graph_caller_old(void);
>> > +extern unsigned long ftrace_graph_regs_call;
>> > +extern void ftrace_graph_regs_caller(void);
>> >
>> > static int __ftrace_modify_caller(unsigned long *callsite,
>> > void (*func) (void), bool enable)
>> > @@ -251,6 +276,14 @@ static int ftrace_modify_graph_caller(bool enable)
>> > ftrace_graph_caller,
>> > enable);
>> >
>> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> > + if (!ret)
>> > + ret = __ftrace_modify_caller(&ftrace_graph_regs_call,
>> > + ftrace_graph_regs_caller,
>> > + enable);
>> > +#endif
>> > +
>> > +
>> > #ifdef CONFIG_OLD_MCOUNT
>> > if (!ret)
>> > ret = __ftrace_modify_caller(&ftrace_graph_call_old,
>> > --
>> > 2.7.4
>> >
>
> I tested it and it works now. An update version of this patch will follow.
> (It also include all fixes for all the other comments on this thread)
>
> Thanks,
> Abel