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

[H.J. Lu]

On Thu, Nov 13, 2025 at 2:46 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 10/11/25 22:55, H.J. Lu wrote:
> > 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.
>
> I changed to:
>
> --
> x86: Fix strstr ifunc on clang
>
> Work around the clang limitation wrt inline function and attribute
> definition, where it does not allow to 'add' new attribute if a
> function is already defined:
>
> Buildint with clang triggers multiple issue on how ifunc macro are
> used:
>
>   ../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).
> --
>
> Ok with this commit message change?

OK.

> >
> >>   ../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.