Re: [for-next][PATCH 2/4] ftrace/x86: Show trampoline call function in enabled_functions

[Steven Rostedt]

H. Peter,

Can you give me your acked-by for this?

Thanks,

-- Steve


On Mon, 27 Oct 2014 14:27:04 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
> 
> The file /sys/kernel/debug/tracing/eneabled_functions is used to debug
> ftrace function hooks. Add to the output what function is being called
> by the trampoline if the arch supports it.
> 
> Add support for this feature in x86_64.
> 
> Cc: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> ---
>  arch/x86/kernel/ftrace.c | 98 ++++++++++++++++++++++++++++++++++++++++++------
>  kernel/trace/ftrace.c    | 22 ++++++++++-
>  2 files changed, 106 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index e4d48f6cad86..ca17c20a1010 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -48,7 +48,7 @@ int ftrace_arch_code_modify_post_process(void)
>  union ftrace_code_union {
>  	char code[MCOUNT_INSN_SIZE];
>  	struct {
> -		char e8;
> +		unsigned char e8;
>  		int offset;
>  	} __attribute__((packed));
>  };
> @@ -797,12 +797,26 @@ static unsigned long create_trampoline(struct ftrace_ops *ops)
>  	return (unsigned long)trampoline;
>  }
>  
> +static unsigned long calc_trampoline_call_offset(bool save_regs)
> +{
> +	unsigned long start_offset;
> +	unsigned long call_offset;
> +
> +	if (save_regs) {
> +		start_offset = (unsigned long)ftrace_regs_caller;
> +		call_offset = (unsigned long)ftrace_regs_call;
> +	} else {
> +		start_offset = (unsigned long)ftrace_caller;
> +		call_offset = (unsigned long)ftrace_call;
> +	}
> +
> +	return call_offset - start_offset;
> +}
> +
>  void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
>  {
>  	ftrace_func_t func;
>  	unsigned char *new;
> -	unsigned long start_offset;
> -	unsigned long call_offset;
>  	unsigned long offset;
>  	unsigned long ip;
>  	int ret;
> @@ -820,15 +834,7 @@ void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
>  			return;
>  	}
>  
> -	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
> -		start_offset = (unsigned long)ftrace_regs_caller;
> -		call_offset = (unsigned long)ftrace_regs_call;
> -	} else {
> -		start_offset = (unsigned long)ftrace_caller;
> -		call_offset = (unsigned long)ftrace_call;
> -	}
> -
> -	offset = call_offset - start_offset;
> +	offset = calc_trampoline_call_offset(ops->flags & FTRACE_OPS_FL_SAVE_REGS);
>  	ip = ops->trampoline + offset;
>  
>  	func = ftrace_ops_get_func(ops);
> @@ -840,6 +846,74 @@ void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
>  	/* The update should never fail */
>  	WARN_ON(ret);
>  }
> +
> +/* Return the address of the function the trampoline calls */
> +static void *addr_from_call(void *ptr)
> +{
> +	union ftrace_code_union calc;
> +	int ret;
> +
> +	ret = probe_kernel_read(&calc, ptr, MCOUNT_INSN_SIZE);
> +	if (WARN_ON_ONCE(ret < 0))
> +		return NULL;
> +
> +	/* Make sure this is a call */
> +	if (WARN_ON_ONCE(calc.e8 != 0xe8)) {
> +		pr_warn("Expected e8, got %x\n", calc.e8);
> +		return NULL;
> +	}
> +
> +	return ptr + MCOUNT_INSN_SIZE + calc.offset;
> +}
> +
> +void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
> +			   unsigned long frame_pointer);
> +
> +/*
> + * If the ops->trampoline was not allocated, then it probably
> + * has a static trampoline func, or is the ftrace caller itself.
> + */
> +static void *static_tramp_func(struct ftrace_ops *ops, struct dyn_ftrace *rec)
> +{
> +	unsigned long offset;
> +	bool save_regs = rec->flags & FTRACE_FL_REGS_EN;
> +	void *ptr;
> +
> +	if (ops && ops->trampoline) {
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +		/*
> +		 * We only know about function graph tracer setting as static
> +		 * trampoline.
> +		 */
> +		if (ops->trampoline == FTRACE_GRAPH_ADDR)
> +			return (void *)prepare_ftrace_return;
> +#endif
> +		return NULL;
> +	}
> +
> +	offset = calc_trampoline_call_offset(save_regs);
> +
> +	if (save_regs)
> +		ptr = (void *)FTRACE_REGS_ADDR + offset;
> +	else
> +		ptr = (void *)FTRACE_ADDR + offset;
> +
> +	return addr_from_call(ptr);
> +}
> +
> +void *arch_ftrace_trampoline_func(struct ftrace_ops *ops, struct dyn_ftrace *rec)
> +{
> +	unsigned long offset;
> +
> +	/* If we didn't allocate this trampoline, consider it static */
> +	if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
> +		return static_tramp_func(ops, rec);
> +
> +	offset = calc_trampoline_call_offset(ops->flags & FTRACE_OPS_FL_SAVE_REGS);
> +	return addr_from_call((void *)ops->trampoline + offset);
> +}
> +
> +
>  #endif /* CONFIG_X86_64 */
>  #endif /* CONFIG_DYNAMIC_FTRACE */
>  
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 15f85eac7e95..422e1f8300b1 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2952,6 +2952,22 @@ static void t_stop(struct seq_file *m, void *p)
>  	mutex_unlock(&ftrace_lock);
>  }
>  
> +void * __weak
> +arch_ftrace_trampoline_func(struct ftrace_ops *ops, struct dyn_ftrace *rec)
> +{
> +	return NULL;
> +}
> +
> +static void add_trampoline_func(struct seq_file *m, struct ftrace_ops *ops,
> +				struct dyn_ftrace *rec)
> +{
> +	void *ptr;
> +
> +	ptr = arch_ftrace_trampoline_func(ops, rec);
> +	if (ptr)
> +		seq_printf(m, " ->%pS", ptr);
> +}
> +
>  static int t_show(struct seq_file *m, void *v)
>  {
>  	struct ftrace_iterator *iter = m->private;
> @@ -2975,19 +2991,21 @@ static int t_show(struct seq_file *m, void *v)
>  
>  	seq_printf(m, "%ps", (void *)rec->ip);
>  	if (iter->flags & FTRACE_ITER_ENABLED) {
> +		struct ftrace_ops *ops = NULL;
> +
>  		seq_printf(m, " (%ld)%s",
>  			   ftrace_rec_count(rec),
>  			   rec->flags & FTRACE_FL_REGS ? " R" : "  ");
>  		if (rec->flags & FTRACE_FL_TRAMP_EN) {
> -			struct ftrace_ops *ops;
> -
>  			ops = ftrace_find_tramp_ops_any(rec);
>  			if (ops)
>  				seq_printf(m, "\ttramp: %pS",
>  					   (void *)ops->trampoline);
>  			else
>  				seq_printf(m, "\ttramp: ERROR!");
> +
>  		}
> +		add_trampoline_func(m, ops, rec);
>  	}	
>  
>  	seq_printf(m, "\n");

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