Re: [PATCH v4 6/6] string: Make strprefix() const-qualifier-generic

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] string: strprefix() fails to compile on const pointers due to
  const_cast()
--

commit 2c70ad25b2785e588ea2435fcf768764945ab8aa
Author: Alejandro Colomar <alx@kernel.org>

string: Make strprefix() const-qualifier-generic

This commit changes strprefix() to return const char * and wraps it in a
macro using const_cast() and CQChar_of() so the return type preserves the
const qualification of the input pointer.

> diff --git a/include/linux/string.h b/include/linux/string.h
> index 25e6e42b5d1e5..e4506a7cff703 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -577,11 +577,12 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
>   * *  @s+strlen(@prefix) if @s starts with @prefix
>   * *  NULL if @s does not start with @prefix
>   */
> -static inline char *strprefix(const char *s, const char *prefix)
> +static inline const char *strprefix(const char *s, const char *prefix)
>  {
>  	size_t len = strlen(prefix);
> -	return strncmp(s, prefix, len) == 0 ? (char *) s + len : NULL;
> +	return strncmp(s, prefix, len) == 0 ? s + len : NULL;
>  }
> +#define strprefix(s, pfx)  const_cast(CQChar_of(s) *, strprefix(s, pfx))

[Severity: High]
Does strprefix() fail to compile when passed a pointer to a
const-qualified type, such as node_name in fwnode_name_eq()?

When s is const-qualified, CQChar_of(s) * resolves to const char *.
Passing that as T to const_cast():

include/linux/stddef.h:
#define const_cast(T, p)  _Generic(p, const T: (T) (p), T: (p))

causes both const T and T in the _Generic selection to expand to
const char *, which fails the build due to duplicate compatible types.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1794425425.git.alx@kernel.org?part=6