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

Jean-Jacques Hiblot
2017-01-25T18:38:51Z

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@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
> + 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
>