Re: [PATCHv5 bpf-next 01/28] ftrace: Add ftrace_hash_count function

[sashiko-bot@kernel.org]

Sashiko AI review found 1 potential issue(s):
- [Low] ftrace_hash_count() is declared under CONFIG_DYNAMIC_FTRACE but defined under CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS, leading to potential linker errors.
--

commit 62c46ea6c0c10abc0df16b7c684809496d439e2f
Author: Jiri Olsa <jolsa@kernel.org>

ftrace: Add ftrace_hash_count function

This commit adds an external ftrace_hash_count function so the hash
count can be obtained outside of the ftrace object.

> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 28b30c6f10314..9d9ae1bc692ae 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -415,6 +415,7 @@ struct ftrace_hash *alloc_ftrace_hash(int size_bits);
>  void free_ftrace_hash(struct ftrace_hash *hash);
>  struct ftrace_func_entry *add_ftrace_hash_entry_direct(struct ftrace_hash *hash,
>  						       unsigned long ip, unsigned long direct);
> +unsigned long ftrace_hash_count(struct ftrace_hash *hash);
>  
>  /* The hash used to know what functions callbacks trace */
>  struct ftrace_ops_hash {

[ ... ]

> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index b2611de3f5943..57ab01fd00bda 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6288,11 +6288,16 @@ int modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
>  }
>  EXPORT_SYMBOL_GPL(modify_ftrace_direct);
>  
> -static unsigned long hash_count(struct ftrace_hash *hash)
> +static inline unsigned long hash_count(struct ftrace_hash *hash)
>  {
>  	return hash ? hash->count : 0;
>  }
>  
> +unsigned long ftrace_hash_count(struct ftrace_hash *hash)
> +{
> +	return hash_count(hash);
> +}
> +

If a kernel is configured with CONFIG_DYNAMIC_FTRACE=y but 
CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS=n, will this result in a linker error?

The declaration in include/linux/ftrace.h is located under 
CONFIG_DYNAMIC_FTRACE, but this definition in kernel/trace/ftrace.c is placed 
inside a CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS block.

Code built-in to the kernel (like BPF or tracing extensions) that attempts 
to use this new API could compile successfully but fail to link on 
architectures that do not support direct ftrace calls.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260417192502.194548-2-jolsa@kernel.org?part=1