[PATCH v4 08/12] x86: Fix strstr ifunc on clang

[H.J. Lu]

On Mon, Nov 10, 2025 at 9:32 PM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> clang triggers multiple issue on how ifunc macro are used:

Please mention the specific clang limitation/feature.

>   ../sysdeps/x86_64/multiarch/strstr.c:38:54: error: attribute declaration must precede definition [-Werror,-Wignored-attributes]
>      38 | extern __typeof (__redirect_strstr) __strstr_generic attribute_hidden;
>         |                                                      ^
>   ./../include/libc-symbols.h:356:43: note: expanded from macro 'attribute_hidden'
>     356 | # define attribute_hidden __attribute__ ((visibility ("hidden")))
>         |                                           ^
>   ../string/strstr.c:76:1: note: previous definition is here
>      76 | STRSTR (const char *haystack, const char *needle)
>         | ^
>   ../sysdeps/x86_64/multiarch/strstr.c:27:16: note: expanded from macro 'STRSTR'
>      27 | #define STRSTR __strstr_generic
>         |                ^
>   ../sysdeps/x86_64/multiarch/strstr.c:65:43: error: redefinition of '__libc_strstr'
>      65 | libc_ifunc_redirected (__redirect_strstr, __libc_strstr, IFUNC_SELECTOR ());
>         |                                           ^
>
> And
>
>   ../sysdeps/x86_64/multiarch/strstr.c:65:43: error: redefinition of '__libc_strstr'
>      65 | libc_ifunc_redirected (__redirect_strstr, __libc_strstr, IFUNC_SELECTOR ());
>         |                                           ^
>   ../sysdeps/x86_64/multiarch/strstr.c:59:13: note: previous definition is here
>      59 | libc_ifunc (__libc_strstr,
>         |             ^
>
> Refactor to use a auxiliary function like other selection (for instance,
> x86_64/multiarch/strcmp.c).
> ---
>  sysdeps/x86_64/multiarch/strstr.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/sysdeps/x86_64/multiarch/strstr.c b/sysdeps/x86_64/multiarch/strstr.c
> index e18e6418aec..f669a57689e 100644
> --- a/sysdeps/x86_64/multiarch/strstr.c
> +++ b/sysdeps/x86_64/multiarch/strstr.c
> @@ -31,19 +31,24 @@
>    __hidden_ver1 (__strstr_generic, __GI_strstr, __strstr_generic);
>  #endif
>
> -#include "string/strstr.c"
> -
>  extern __typeof (__redirect_strstr) __strstr_sse2_unaligned attribute_hidden;
>  extern __typeof (__redirect_strstr) __strstr_generic attribute_hidden;
>
> +#include "string/strstr.c"
> +
>  #include "init-arch.h"
>
> -/* Avoid DWARF definition DIE on ifunc symbol so that GDB can handle
> -   ifunc symbol properly.  */
> -extern __typeof (__redirect_strstr) __libc_strstr;
> -libc_ifunc (__libc_strstr,
> -           HAS_ARCH_FEATURE (Fast_Unaligned_Load)
> -           ? __strstr_sse2_unaligned
> -           : __strstr_generic)
> +static inline void *
> +IFUNC_SELECTOR (void)
> +{
> +  const struct cpu_features *cpu_features = __get_cpu_features ();
> +
> +  if (CPU_FEATURES_ARCH_P (cpu_features, Fast_Unaligned_Load))
> +    return __strstr_sse2_unaligned;
> +
> +  return __strstr_generic;
> +}
> +
> +libc_ifunc_redirected (__redirect_strstr, __libc_strstr, IFUNC_SELECTOR ());
>  #undef strstr
>  strong_alias (__libc_strstr, strstr)
> --
> 2.43.0
>


-- 
H.J.