Re: [RFC PATCH v1 1/1] tracing/kprobes: Return ENAMESVRLSYMS when func matches several symbols

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Hi Francis,

On Wed, 23 Aug 2023 18:14:10 +0200
Francis Laniel <flaniel@xxxxxxxxxxxxxxxxxxx> wrote:

> Previously to this commit, if func matches several symbols, a PMU kprobe would
> be installed for the first matching address.
> This could lead to some misunderstanding when some BPF code was never called
> because it was attached to a function which was indeed not call, because the
> effectively called one has no kprobes.
> 
> So, this commit introduces ENAMESVRLSYMS which is returned when func matches
> several symbols.

The trace_kprobe part looks good to me.
But sorry, I mislead you. I meant using an existing error code as a metaphor.
EINVAL is used everywhere, so choose another error code, e.g. EADDRNOTAVAIL.

Also, can you add this check in __trace_kprobe_create()?
I think right before below code, at that point, 'symbol' has the symbol name.

        trace_probe_log_set_index(0);
        if (event) {
                ret = traceprobe_parse_event_name(&event, &group, gbuf,
                                                  event - argv[0]);
                if (ret)
                        goto parse_error;
        }


Thank you,

> This way, user needs to use addr to remove the ambiguity.
> 
> Suggested-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Signed-off-by: Francis Laniel <flaniel@xxxxxxxxxxxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@xxxxxxxxxx/
> ---
>  arch/alpha/include/uapi/asm/errno.h        |  2 ++
>  arch/mips/include/uapi/asm/errno.h         |  2 ++
>  arch/parisc/include/uapi/asm/errno.h       |  2 ++
>  arch/sparc/include/uapi/asm/errno.h        |  2 ++
>  include/uapi/asm-generic/errno.h           |  2 ++
>  kernel/trace/trace_kprobe.c                | 26 ++++++++++++++++++++++
>  tools/arch/alpha/include/uapi/asm/errno.h  |  2 ++
>  tools/arch/mips/include/uapi/asm/errno.h   |  2 ++
>  tools/arch/parisc/include/uapi/asm/errno.h |  2 ++
>  tools/arch/sparc/include/uapi/asm/errno.h  |  2 ++
>  tools/include/uapi/asm-generic/errno.h     |  2 ++
>  11 files changed, 46 insertions(+)
> 
> diff --git a/arch/alpha/include/uapi/asm/errno.h b/arch/alpha/include/uapi/asm/errno.h
> index 3d265f6babaf..3d9686d915f9 100644
> --- a/arch/alpha/include/uapi/asm/errno.h
> +++ b/arch/alpha/include/uapi/asm/errno.h
> @@ -125,4 +125,6 @@
> 
>  #define EHWPOISON	139	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	140	/* Name correspond to several symbols */
> +
>  #endif
> diff --git a/arch/mips/include/uapi/asm/errno.h b/arch/mips/include/uapi/asm/errno.h
> index 2fb714e2d6d8..1fd64ee7b629 100644
> --- a/arch/mips/include/uapi/asm/errno.h
> +++ b/arch/mips/include/uapi/asm/errno.h
> @@ -124,6 +124,8 @@
> 
>  #define EHWPOISON	168	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	169	/* Name correspond to several symbols */
> +
>  #define EDQUOT		1133	/* Quota exceeded */
> 
> 
> diff --git a/arch/parisc/include/uapi/asm/errno.h b/arch/parisc/include/uapi/asm/errno.h
> index 87245c584784..c7845ceece26 100644
> --- a/arch/parisc/include/uapi/asm/errno.h
> +++ b/arch/parisc/include/uapi/asm/errno.h
> @@ -124,4 +124,6 @@
> 
>  #define EHWPOISON	257	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	258	/* Name correspond to several symbols */
> +
>  #endif
> diff --git a/arch/sparc/include/uapi/asm/errno.h b/arch/sparc/include/uapi/asm/errno.h
> index 81a732b902ee..1ed065943bab 100644
> --- a/arch/sparc/include/uapi/asm/errno.h
> +++ b/arch/sparc/include/uapi/asm/errno.h
> @@ -115,4 +115,6 @@
> 
>  #define EHWPOISON	135	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	136	/* Name correspond to several symbols */
> +
>  #endif
> diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h
> index cf9c51ac49f9..3d5d5740c8da 100644
> --- a/include/uapi/asm-generic/errno.h
> +++ b/include/uapi/asm-generic/errno.h
> @@ -120,4 +120,6 @@
> 
>  #define EHWPOISON	133	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	134	/* Name correspond to several symbols */
> +
>  #endif
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 23dba01831f7..53b66db1ff53 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1699,6 +1699,16 @@ static int unregister_kprobe_event(struct trace_kprobe *tk)
>  }
> 
>  #ifdef CONFIG_PERF_EVENTS
> +
> +static int count_symbols(void *data, unsigned long unused)
> +{
> +	unsigned int *count = data;
> +
> +	(*count)++;
> +
> +	return 0;
> +}
> +
>  /* create a trace_kprobe, but don't add it to global lists */
>  struct trace_event_call *
>  create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> @@ -1709,6 +1719,22 @@ create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
>  	int ret;
>  	char *event;
> 
> +	/*
> +	 * If user specifies func, we check that the function name does not
> +	 * correspond to several symbols.
> +	 * If this is the case, we return with error code ENAMESVRLSYMS to
> +	 * indicate the user he/she should use addr and offs rather than func to
> +	 * remove the ambiguity.
> +	 */
> +	if (func) {
> +		unsigned int count;
> +
> +		count = 0;
> +		kallsyms_on_each_match_symbol(count_symbols, func, &count);
> +		if (count > 1)
> +			return ERR_PTR(-ENAMESVRLSYMS);
> +	}
> +
>  	/*
>  	 * local trace_kprobes are not added to dyn_event, so they are never
>  	 * searched in find_trace_kprobe(). Therefore, there is no concern of
> diff --git a/tools/arch/alpha/include/uapi/asm/errno.h b/tools/arch/alpha/include/uapi/asm/errno.h
> index 3d265f6babaf..3d9686d915f9 100644
> --- a/tools/arch/alpha/include/uapi/asm/errno.h
> +++ b/tools/arch/alpha/include/uapi/asm/errno.h
> @@ -125,4 +125,6 @@
> 
>  #define EHWPOISON	139	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	140	/* Name correspond to several symbols */
> +
>  #endif
> diff --git a/tools/arch/mips/include/uapi/asm/errno.h b/tools/arch/mips/include/uapi/asm/errno.h
> index 2fb714e2d6d8..1fd64ee7b629 100644
> --- a/tools/arch/mips/include/uapi/asm/errno.h
> +++ b/tools/arch/mips/include/uapi/asm/errno.h
> @@ -124,6 +124,8 @@
> 
>  #define EHWPOISON	168	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	169	/* Name correspond to several symbols */
> +
>  #define EDQUOT		1133	/* Quota exceeded */
> 
> 
> diff --git a/tools/arch/parisc/include/uapi/asm/errno.h b/tools/arch/parisc/include/uapi/asm/errno.h
> index 87245c584784..c7845ceece26 100644
> --- a/tools/arch/parisc/include/uapi/asm/errno.h
> +++ b/tools/arch/parisc/include/uapi/asm/errno.h
> @@ -124,4 +124,6 @@
> 
>  #define EHWPOISON	257	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	258	/* Name correspond to several symbols */
> +
>  #endif
> diff --git a/tools/arch/sparc/include/uapi/asm/errno.h b/tools/arch/sparc/include/uapi/asm/errno.h
> index 81a732b902ee..1ed065943bab 100644
> --- a/tools/arch/sparc/include/uapi/asm/errno.h
> +++ b/tools/arch/sparc/include/uapi/asm/errno.h
> @@ -115,4 +115,6 @@
> 
>  #define EHWPOISON	135	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	136	/* Name correspond to several symbols */
> +
>  #endif
> diff --git a/tools/include/uapi/asm-generic/errno.h b/tools/include/uapi/asm-generic/errno.h
> index cf9c51ac49f9..3d5d5740c8da 100644
> --- a/tools/include/uapi/asm-generic/errno.h
> +++ b/tools/include/uapi/asm-generic/errno.h
> @@ -120,4 +120,6 @@
> 
>  #define EHWPOISON	133	/* Memory page has hardware error */
> 
> +#define ENAMESVRLSYMS	134	/* Name correspond to several symbols */
> +
>  #endif
> --
> 2.34.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>



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