Re: [PATCH v5 24/34] fprobe: Use ftrace_regs in fprobe entry handler

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Dec 18, 2023 at 10:16:23PM +0900, Masami Hiramatsu (Google) wrote:

SNIP

> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 84e8a0f6e4e0..d3f8745d8ead 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2503,7 +2503,7 @@ static int __init bpf_event_init(void)
>  fs_initcall(bpf_event_init);
>  #endif /* CONFIG_MODULES */
>  
> -#ifdef CONFIG_FPROBE
> +#if defined(CONFIG_FPROBE) && defined(CONFIG_DYNAMIC_FTRACE_WITH_REGS)
>  struct bpf_kprobe_multi_link {
>  	struct bpf_link link;
>  	struct fprobe fp;
> @@ -2733,10 +2733,14 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
>  
>  static int
>  kprobe_multi_link_handler(struct fprobe *fp, unsigned long fentry_ip,
> -			  unsigned long ret_ip, struct pt_regs *regs,
> +			  unsigned long ret_ip, struct ftrace_regs *fregs,
>  			  void *data)
>  {
>  	struct bpf_kprobe_multi_link *link;
> +	struct pt_regs *regs = ftrace_get_regs(fregs);
> +
> +	if (!regs)
> +		return 0;
>  
>  	link = container_of(fp, struct bpf_kprobe_multi_link, fp);
>  	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
> @@ -3008,7 +3012,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>  	kvfree(cookies);
>  	return err;
>  }
> -#else /* !CONFIG_FPROBE */
> +#else /* !CONFIG_FPROBE || !CONFIG_DYNAMIC_FTRACE_WITH_REGS */
>  int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
>  {
>  	return -EOPNOTSUPP;
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index 6cd2a4e3afb8..f12569494d8a 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -46,7 +46,7 @@ static inline void __fprobe_handler(unsigned long ip, unsigned long parent_ip,
>  	}
>  
>  	if (fp->entry_handler)
> -		ret = fp->entry_handler(fp, ip, parent_ip, ftrace_get_regs(fregs), entry_data);
> +		ret = fp->entry_handler(fp, ip, parent_ip, fregs, entry_data);
>  
>  	/* If entry_handler returns !0, nmissed is not counted. */
>  	if (rh) {
> @@ -182,7 +182,7 @@ static void fprobe_init(struct fprobe *fp)
>  		fp->ops.func = fprobe_kprobe_handler;
>  	else
>  		fp->ops.func = fprobe_handler;
> -	fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS;
> +	fp->ops.flags |= FTRACE_OPS_FL_SAVE_ARGS;

so with this change you move to ftrace_caller trampoline,
but we need ftrace_regs_caller right?

otherwise the (!regs) check in kprobe_multi_link_handler
will be allways true IIUC

jirka

>  }
>  
>  static int fprobe_init_rethook(struct fprobe *fp, int num)
> diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
> index 7d2ddbcfa377..ef6b36fd05ae 100644
> --- a/kernel/trace/trace_fprobe.c
> +++ b/kernel/trace/trace_fprobe.c
> @@ -320,12 +320,16 @@ NOKPROBE_SYMBOL(fexit_perf_func);
>  #endif	/* CONFIG_PERF_EVENTS */
>  
>  static int fentry_dispatcher(struct fprobe *fp, unsigned long entry_ip,
> -			     unsigned long ret_ip, struct pt_regs *regs,
> +			     unsigned long ret_ip, struct ftrace_regs *fregs,
>  			     void *entry_data)
>  {
>  	struct trace_fprobe *tf = container_of(fp, struct trace_fprobe, fp);
> +	struct pt_regs *regs = ftrace_get_regs(fregs);
>  	int ret = 0;
>  
> +	if (!regs)
> +		return 0;
> +
>  	if (trace_probe_test_flag(&tf->tp, TP_FLAG_TRACE))
>  		fentry_trace_func(tf, entry_ip, regs);
>  #ifdef CONFIG_PERF_EVENTS
> diff --git a/lib/test_fprobe.c b/lib/test_fprobe.c
> index 24de0e5ff859..ff607babba18 100644
> --- a/lib/test_fprobe.c
> +++ b/lib/test_fprobe.c
> @@ -40,7 +40,7 @@ static noinline u32 fprobe_selftest_nest_target(u32 value, u32 (*nest)(u32))
>  
>  static notrace int fp_entry_handler(struct fprobe *fp, unsigned long ip,
>  				    unsigned long ret_ip,
> -				    struct pt_regs *regs, void *data)
> +				    struct ftrace_regs *fregs, void *data)
>  {
>  	KUNIT_EXPECT_FALSE(current_test, preemptible());
>  	/* This can be called on the fprobe_selftest_target and the fprobe_selftest_target2 */
> @@ -81,7 +81,7 @@ static notrace void fp_exit_handler(struct fprobe *fp, unsigned long ip,
>  
>  static notrace int nest_entry_handler(struct fprobe *fp, unsigned long ip,
>  				      unsigned long ret_ip,
> -				      struct pt_regs *regs, void *data)
> +				      struct ftrace_regs *fregs, void *data)
>  {
>  	KUNIT_EXPECT_FALSE(current_test, preemptible());
>  	return 0;
> diff --git a/samples/fprobe/fprobe_example.c b/samples/fprobe/fprobe_example.c
> index 64e715e7ed11..1545a1aac616 100644
> --- a/samples/fprobe/fprobe_example.c
> +++ b/samples/fprobe/fprobe_example.c
> @@ -50,7 +50,7 @@ static void show_backtrace(void)
>  
>  static int sample_entry_handler(struct fprobe *fp, unsigned long ip,
>  				unsigned long ret_ip,
> -				struct pt_regs *regs, void *data)
> +				struct ftrace_regs *fregs, void *data)
>  {
>  	if (use_trace)
>  		/*
>