Re: [PATCH v2] tracing: fprobe: use ftrace if CONFIG_DYNAMIC_FTRACE_WITH_ARGS

[Menglong Dong <menglong.dong@linux.dev>]

On 2025/11/3 11:16, Masami Hiramatsu wrote:
> On Fri, 31 Oct 2025 10:40:38 +0800
> Menglong Dong <menglong8.dong@gmail.com> wrote:
> 
> > For now, we will use ftrace for the fprobe if fp->exit_handler not exists
> > and CONFIG_DYNAMIC_FTRACE_WITH_REGS is enabled.
> > 
> > However, CONFIG_DYNAMIC_FTRACE_WITH_REGS is not supported by some arch,
> > such as arm. What we need in the fprobe is the function arguments, so we
> > can use ftrace for fprobe if CONFIG_DYNAMIC_FTRACE_WITH_ARGS is enabled.
> > 
> > Therefore, use ftrace if CONFIG_DYNAMIC_FTRACE_WITH_REGS or
> > CONFIG_DYNAMIC_FTRACE_WITH_ARGS enabled.
> > 
> > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > ---
> > v2:
> > - remove the definition of FPROBE_USE_FTRACE
> > ---
> >  kernel/trace/fprobe.c | 30 +++++++++++++++++++-----------
> >  1 file changed, 19 insertions(+), 11 deletions(-)
> > 
> > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> > index ecd623eef68b..742ad5a61d46 100644
> > --- a/kernel/trace/fprobe.c
> > +++ b/kernel/trace/fprobe.c
> > @@ -44,6 +44,7 @@
> >  static struct hlist_head fprobe_table[FPROBE_TABLE_SIZE];
> >  static struct rhltable fprobe_ip_table;
> >  static DEFINE_MUTEX(fprobe_mutex);
> > +static struct fgraph_ops fprobe_graph_ops;
> >  
> >  static u32 fprobe_node_hashfn(const void *data, u32 len, u32 seed)
> >  {
> > @@ -254,7 +255,7 @@ static inline int __fprobe_kprobe_handler(unsigned long ip, unsigned long parent
> >  	return ret;
> >  }
> >  
> > -#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> > +#if defined(CONFIG_DYNAMIC_FTRACE_WITH_ARGS) || defined(CONFIG_DYNAMIC_FTRACE_WITH_REGS)
> >  /* ftrace_ops callback, this processes fprobes which have only entry_handler. */
> >  static void fprobe_ftrace_entry(unsigned long ip, unsigned long parent_ip,
> >  	struct ftrace_ops *ops, struct ftrace_regs *fregs)
> > @@ -295,7 +296,7 @@ NOKPROBE_SYMBOL(fprobe_ftrace_entry);
> >  
> >  static struct ftrace_ops fprobe_ftrace_ops = {
> >  	.func	= fprobe_ftrace_entry,
> > -	.flags	= FTRACE_OPS_FL_SAVE_REGS,
> > +	.flags	= FTRACE_OPS_FL_SAVE_ARGS,
> >  };
> >  static int fprobe_ftrace_active;
> >  
> > @@ -335,6 +336,13 @@ static bool fprobe_is_ftrace(struct fprobe *fp)
> >  {
> >  	return !fp->exit_handler;
> >  }
> > +
> 
> Ah, the new function depends on MODULES. 
> 
> #ifdef CONFIG_MODULES
> 
> > +static void fprobe_set_ips(unsigned long *ips, unsigned int cnt, int remove,
> > +			   int reset)
> > +{
> > +	ftrace_set_filter_ips(&fprobe_graph_ops.ops, ips, cnt, remove, reset);
> > +	ftrace_set_filter_ips(&fprobe_ftrace_ops, ips, cnt, remove, reset);
> > +}
> 
> #endif	/* CONFIG_MODULES */

Yeah, I saw the CI's build warning. I'll send a V3 to fix
this issue.

Thanks!
Menglong Dong

> 
> >  #else
> 
> #ifdef CONFIG_MODULES
> 
> >  static int fprobe_ftrace_add_ips(unsigned long *addrs, int num)
> >  {
> > @@ -349,7 +357,13 @@ static bool fprobe_is_ftrace(struct fprobe *fp)
> >  {
> >  	return false;
> >  }
> 
> #endif	/* CONFIG_MODULES */
> 
> are needed.
> 
> Thank you,
> 
> > -#endif
> > +
> > +static void fprobe_set_ips(unsigned long *ips, unsigned int cnt, int remove,
> > +			   int reset)
> > +{
> > +	ftrace_set_filter_ips(&fprobe_graph_ops.ops, ips, cnt, remove, reset);
> > +}
> > +#endif /* !CONFIG_DYNAMIC_FTRACE_WITH_ARGS && !CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >  
> >  /* fgraph_ops callback, this processes fprobes which have exit_handler. */
> >  static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops,
> > @@ -596,14 +610,8 @@ static int fprobe_module_callback(struct notifier_block *nb,
> >  	} while (node == ERR_PTR(-EAGAIN));
> >  	rhashtable_walk_exit(&iter);
> >  
> > -	if (alist.index > 0) {
> > -		ftrace_set_filter_ips(&fprobe_graph_ops.ops,
> > -				      alist.addrs, alist.index, 1, 0);
> > -#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> > -		ftrace_set_filter_ips(&fprobe_ftrace_ops,
> > -				      alist.addrs, alist.index, 1, 0);
> > -#endif
> > -	}
> > +	if (alist.index > 0)
> > +		fprobe_set_ips(alist.addrs, alist.index, 1, 0);
> >  	mutex_unlock(&fprobe_mutex);
> >  
> >  	kfree(alist.addrs);
> 
> 
>