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Date:   Wed, 25 Jan 2017 19:30:32 +0100
From:   Jean-Jacques Hiblot <jjhiblot@...phandler.com>
To:     Abel Vesa <abelvesa@...ux.com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
        viro@...iv.linux.org.uk,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jean-Jacques Hiblot <jjhiblot@...phandler.com>,
        Petr Mladek <pmladek@...e.com>, robin.murphy@....com,
        zhouchengming1@...wei.com, Abel Vesa <abelvesa@...il.com>
Subject: Re: [PATCHv2] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS

Abel, I tested it partially.
It's seems OK if I have FRAME_POINTER enabled and it breaks otherwise.

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@...ux.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@...ux.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
> +       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)
> 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);
> +}
> +
> +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
>

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