Re: [PATCH v4] sysdeps/x86_64/multiarch/memmem-avx2.c: add memmem-avx2.c

[James <tirtajames45@gmail.com>]

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On Sat, Feb 3, 2024 at 5:48 AM Noah Goldstein <goldstein.w.n@gmail.com>
wrote:

> On Thu, Feb 1, 2024 at 1:00 AM James Tirta Halim <tirtajames45@gmail.com>
> wrote:
> >
> > Find the rarest byte in NE. Find the parts of HS that matches the rare
> byte
> > and the byte after it. If found, shift back to the start of NE in HS and
> > vector compare the first VEC_SIZE with NE. If matches, compare the rest
> > with MEMCMPEQ.
> >
> > Timings (Core i3-1115G4):
> > basic_memmem twoway_memmem __memmem_avx512 __memmem_avx2
> > __memmem_generic
> > Total:
> > 6.80124e+06 1.06087e+06 219483 345385 768041
> > Average:
> > 25958.9 4049.11 837.721 1318.26 2931.45
> >
> > Passes make check.
> >
> > Changes in v1:
> > 1. Add memmem-avx2.c
> >
> > Changes in v2:
> > 1. Add avx512 support with a generic header file
> > 2. Use __memcmpeq instead of memcmp
> > 3. Remove scalar loop
> > 4. Fix unsafe unaligned load
> >
> > Changes in v3:
> > 1. Avoid checking for alignment to the start of the page since that will
> be rare
> > 2. Use __memcmpeq instead of __memcmpeq_avx2 (it generates undefined
> > reference errors)
> > 3. Add memmem.c (needs review)
> > 4. Add __memcmpeq_avx2 and __memcmpeq_avx512 to ifunc-impl-list.c (needs
> > review)
> > 5. Add libc_hidden_builtin_def and MEMMEM to memmem.c (needs review)
> >
> > Changes in v4:
> > 1. Correct the cpu feature checks in ifunc-impl-list.c and memmem.c to
> > use AVX512BW and BMI1 for AVX512 and AVX2 and BMI1 for AVX2
> > 2. Correct the Makefile to use the appropriate flags
> > 3. Rename memmem-vectorized-avx.h to memmem-avx-base.h
> > 4. Remove unused vector macros (POPCNT and LZCNT)
> >
> > ---
> >  string/memmem.c                            |   7 +-
> >  sysdeps/x86_64/multiarch/Makefile          |   5 +
> >  sysdeps/x86_64/multiarch/ifunc-impl-list.c |  12 ++
> >  sysdeps/x86_64/multiarch/memmem-avx-base.h | 217 +++++++++++++++++++++
> >  sysdeps/x86_64/multiarch/memmem-avx2.c     |   3 +
> >  sysdeps/x86_64/multiarch/memmem-avx512.c   |  16 ++
> >  sysdeps/x86_64/multiarch/memmem.c          |  67 +++++++
> >  7 files changed, 326 insertions(+), 1 deletion(-)
> >  create mode 100644 sysdeps/x86_64/multiarch/memmem-avx-base.h
> >  create mode 100644 sysdeps/x86_64/multiarch/memmem-avx2.c
> >  create mode 100644 sysdeps/x86_64/multiarch/memmem-avx512.c
> >  create mode 100644 sysdeps/x86_64/multiarch/memmem.c
> >
> > diff --git a/string/memmem.c b/string/memmem.c
> > index 6badc1c3bd..62654b4bd0 100644
> > --- a/string/memmem.c
> > +++ b/string/memmem.c
> > @@ -32,6 +32,10 @@
> >
> >  #undef memmem
> >
> > +#ifndef MEMMEM
> > +#      define MEMMEM __memmem
> > +#endif
> > +
> >  /* Hash character pairs so a small shift table can be used.  All bits of
> >     p[0] are included, but not all bits from p[-1].  So if two equal
> hashes
> >     match on p[-1], p[0] matches too.  Hash collisions are harmless and
> result
> > @@ -50,7 +54,7 @@
> >     The limit also implies worst-case performance is linear.
> >     Needles larger than 256 characters use the linear-time Two-Way
> algorithm.  */
> >  void *
> > -__memmem(const void *haystack, size_t hs_len,
> > +MEMMEM(const void *haystack, size_t hs_len,
> >  const void *needle, size_t ne_len)
> >  {
> >         const unsigned char *hs = (const unsigned char *)haystack;
> > @@ -122,3 +126,4 @@ const void *needle, size_t ne_len)
> >  libc_hidden_def(__memmem)
> >  weak_alias(__memmem, memmem)
> >  libc_hidden_weak(memmem)
> > +libc_hidden_builtin_def(MEMMEM)
> > diff --git a/sysdeps/x86_64/multiarch/Makefile
> b/sysdeps/x86_64/multiarch/Makefile
> > index e1e894c963..95c95eee4b 100644
> > --- a/sysdeps/x86_64/multiarch/Makefile
> > +++ b/sysdeps/x86_64/multiarch/Makefile
> > @@ -15,6 +15,8 @@ sysdep_routines += \
> >    memcmpeq-avx2-rtm \
> >    memcmpeq-evex \
> >    memcmpeq-sse2 \
> > +  memmem-avx2 \
> > +  memmem-avx512 \
> >    memmove-avx-unaligned-erms \
> >    memmove-avx-unaligned-erms-rtm \
> >    memmove-avx512-no-vzeroupper \
> > @@ -122,6 +124,9 @@ sysdep_routines += \
> >    varshift \
> >  # sysdep_routines
> >
> > +CFLAGS-memmem-avx2.c += -mavx2 -mbmi -O3
> > +CFLAGS-memmem-avx512.c += -mavx512f -mavx512bw -mbmi -O3
> > +
> >  CFLAGS-strcspn-sse4.c += -msse4
> >  CFLAGS-strpbrk-sse4.c += -msse4
> >  CFLAGS-strspn-sse4.c += -msse4
> > diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> > index 5427ff1907..300d4064ae 100644
> > --- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> > +++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> > @@ -799,6 +799,18 @@ __libc_ifunc_impl_list (const char *name, struct
> libc_ifunc_impl *array,
> >               IFUNC_IMPL_ADD (array, i, strstr, 1,
> __strstr_sse2_unaligned)
> >               IFUNC_IMPL_ADD (array, i, strstr, 1, __strstr_generic))
> >
> > +  /* Support sysdeps/x86_64/multiarch/memmem.c.  */
> > +  IFUNC_IMPL (i, name, memmem,
> > +              IFUNC_IMPL_ADD (array, i, memmem,
> > +                              (CPU_FEATURE_USABLE (AVX512BW)
> > +                               && CPU_FEATURE_USABLE (BMI1)),
> > +                              __memmem_avx512)
> > +              IFUNC_IMPL_ADD (array, i, memmem,
> > +                             (CPU_FEATURE_USABLE (AVX2)
> > +                             && CPU_FEATURE_USABLE (BMI1)),
> > +                             __memmem_avx2)
> > +             IFUNC_IMPL_ADD (array, i, memmem, 1, __memmem_generic))
> > +
> >    /* Support sysdeps/x86_64/multiarch/wcschr.c.  */
> >    IFUNC_IMPL (i, name, wcschr,
> >               X86_IFUNC_IMPL_ADD_V4 (array, i, wcschr,
> > diff --git a/sysdeps/x86_64/multiarch/memmem-avx-base.h
> b/sysdeps/x86_64/multiarch/memmem-avx-base.h
> > new file mode 100644
> > index 0000000000..46883bb121
> > --- /dev/null
> > +++ b/sysdeps/x86_64/multiarch/memmem-avx-base.h
> > @@ -0,0 +1,217 @@
> > +#include <immintrin.h>
> > +#include <inttypes.h>
> > +#include <string.h>
> > +#include <libc-pointer-arith.h>
> > +
> > +#ifndef FUNC_NAME
> > +#  define __memmem_avx2
> > +#endif
> > +#ifndef VEC
> > +#  define VEC __m256i
> > +#endif
> > +#ifndef VEC_SIZE
> > +#  define VEC_SIZE sizeof (VEC)
> > +#endif
> > +#ifndef MASK
> > +#  define MASK uint32_t
> > +#endif
> > +#ifndef MASK_SIZE
> > +#  define MASK_SIZE sizeof (MASK)
> > +#endif
> > +#ifndef LOAD
> > +#  define LOAD(x) _mm256_load_si256 (x)
> > +#endif
> > +#ifndef LOADU
> > +#  define LOADU(x) _mm256_loadu_si256 (x)
> > +#endif
> > +#ifndef STORE
> > +#  define STORE(dst, src) _mm256_store_si256 (dst, src)
> > +#endif
> > +#ifndef STOREU
> > +#  define STOREU(dst, src) _mm256_storeu_si256 (dst, src)
> > +#endif
> > +#ifndef CMPEQ8_MASK
> > +#  define CMPEQ8_MASK(x, y) _mm256_movemask_epi8 (_mm256_cmpeq_epi8 (x,
> y))
> > +#endif
> > +#ifndef SETZERO
> > +#  define SETZERO(x) _mm256_setzero_si256 (x)
> > +#endif
> > +#ifndef SETONE8
> > +#  define SETONE8(x) _mm256_set1_epi8 (x)
> > +#endif
> > +#ifndef TZCNT
> > +#  define TZCNT(x) _tzcnt_u32 (x)
> > +#endif
> > +#ifndef BLSR
> > +#  define BLSR(x) _blsr_u32 (x)
> > +#endif
> > +#ifndef ONES
> > +#  define ONES ((MASK) -1)
> > +#endif
> > +
> Things like `ONE`, `VEC_SIZE`, `MASK_SIZE`, etc...
> can just be unconditionally defined in memmem-avx-base
>
> Also, instead of having a default in memmem-avx-base,
> think the rest should be just be defined in the memem-avx2/memem-avx512.
> Otherwise theres not really preventing the `TZCNT`/`BLSR` from becoming
> desynced with `MASK` (likewise for the VEC defines).
>
AVX2 macros are still defined in memmem-avx-base.h because otherwise, IDEs
will show undeclared identifier errors when editing memmem-avx-base.h.
>
>
> > +#ifndef MEMCMPEQ
> > +#  define MEMCMPEQ __memcmpeq
> > +#endif
> > +#ifndef MEMCPY
> > +#  define MEMCPY memcpy
> > +#endif
> > +#ifndef MEMCHR
> > +#  define MEMCHR memchr
> > +#endif
> > +#ifndef PAGE_SIZE
> > +#  define PAGE_SIZE 4096
> > +#endif
> > +#define MIN(x, y) (((x) < (y)) ? (x) : (y))
> > +
> > +static inline void *
> > +find_rarest_byte (const void *ne, size_t n)
> > +{
> > +  /* Lower is rarer. The table is based on the
> > +   *.c and *.h files in glibc. */
> > +  static const unsigned char rarebyte_table[256]
> > +      = { 0,   1,   13,         56,  59,  60,  61,  62,  63,  232, 248,
> 2,   158, 4,
> > +         5,   6,   7,   8,   9,   10,  14,  20,  26,  29,  37,  46,
> 52,  53,
> > +         54,  55,  57,  58,  255, 172, 242, 193, 162, 174, 178, 182,
> 218, 219,
> > +         212, 180, 249, 197, 221, 210, 253, 231, 230, 224, 225, 226,
> 227, 223,
> > +         222, 220, 176, 213, 184, 229, 188, 164, 159, 209, 181, 203,
> 189, 216,
> > +         196, 192, 185, 205, 161, 168, 215, 187, 211, 194, 195, 165,
> 206, 204,
> > +         214, 198, 173, 179, 175, 183, 167, 202, 239, 201, 160, 241,
> 163, 246,
> > +         233, 238, 240, 254, 237, 208, 234, 250, 169, 186, 236, 217,
> 245, 243,
> > +         228, 170, 247, 244, 251, 235, 199, 200, 252, 207, 177, 191,
> 171, 190,
> > +         166, 3,   140, 134, 124, 126, 86,  128, 95,  117, 114, 93,
> 81,  87,
> > +         132, 96,  112, 97,  103, 82,  139, 89,  98,  88,  119, 74,
> 156, 115,
> > +         104, 75,  120, 106, 76,  155, 90,  122, 107, 125, 152, 145,
> 136, 137,
> > +         101, 116, 102, 108, 99,  141, 77,  78,  118, 79,  109, 100,
> 150, 73,
> > +         94,  72,  121, 151, 113, 135, 110, 105, 83,  91,  11,  12,
> 64,  149,
> > +         146, 111, 65,  69,  66,  15,  16,  17,  18,  19,  130, 92,
> 144, 123,
> > +         21,  22,  23,  24,  131, 133, 127, 142, 25,  70,  129, 27,
> 28,  67,
> > +         153, 84,  143, 138, 147, 157, 148, 68,  71,  30,  31,  32,
> 33,  34,
> > +         35,  36,  154, 38,  39,  40,  41,  42,  80,  43,  44,  45,
> 47,  48,
> > +         85,  49,  50,  51 };
> > +  const unsigned char *rare = (const unsigned char *) ne;
> > +  const unsigned char *p = (const unsigned char *) ne;
> > +  int c_rare = rarebyte_table[*rare];
> > +  int c;
> > +  for (; n--; ++p)
> > +    {
> > +      c = rarebyte_table[*p];
> > +      if (c < c_rare)
> > +       {
> > +         rare = p;
> > +         c_rare = c;
> > +       }
> > +    }
> > +  return (void *) rare;
> > +}
> > +
> > +void *
> > +FUNC_NAME (const void *hs, size_t hs_len, const void *ne, size_t ne_len)
> > +{
> > +  if (ne_len == 1)
> > +    return (void *) MEMCHR (hs, *(unsigned char *) ne, hs_len);
> > +  if (__glibc_unlikely (ne_len == 0))
> > +    return (void *) hs;
> > +  if (__glibc_unlikely (hs_len < ne_len))
> > +    return NULL;
> > +  VEC hv0, hv1, hv, nv;
> > +  MASK i, hm0, hm1, m, cmpm;
> > +  const unsigned int matchsh = ne_len < VEC_SIZE ? VEC_SIZE - ne_len :
> 0;
> > +  const MASK matchm = ONES << matchsh;
> > +  const unsigned char *h = (const unsigned char *) hs;
> > +  const unsigned char *const end = h + hs_len - ne_len;
> > +  const unsigned char *hp;
> > +  size_t shift = PTR_DIFF (find_rarest_byte (ne, ne_len), ne);
> think ne_len here should be probably limitted to something like
> MIN(ne_len, VEC_SIZE).
>
Done in v5.

> > +  if (shift == ne_len - 1)
> > +    --shift;
> > +  const VEC nv0 = SETONE8 (*((char *) ne + shift));
> > +  const VEC nv1 = SETONE8 (*((char *) ne + shift + 1));
> > +  h += shift;
> > +  if (PTR_DIFF (PTR_ALIGN_UP (ne, PAGE_SIZE), ne) >= VEC_SIZE
> > +      || PTR_IS_ALIGNED (ne, PAGE_SIZE) || ne_len >= VEC_SIZE)
> > +    nv = LOADU ((VEC *) ne);
> think simpler logic is `(ne & (PAGE_SIZE - 1)) > (PAGE_SIZE - VEC_SIZE)`
>
Done in v5.

> > +  else
> > +    MEMCPY (&nv, ne, MIN (VEC_SIZE, ne_len));
> > +  const unsigned int off = PTR_DIFF (h, PTR_ALIGN_DOWN (h, VEC_SIZE));
> > +  unsigned int off2 = (PTR_DIFF (end, (h - shift)) < VEC_SIZE)
> > +                         ? VEC_SIZE - (unsigned int) (end - (h -
> shift)) - 1
> > +                         : 0;
> > +  h -= off;
> > +  hv0 = LOAD ((const VEC *) h);
> > +  hm0 = (MASK) CMPEQ8_MASK (hv0, nv0);
> > +  hm1 = (MASK) CMPEQ8_MASK (hv0, nv1) >> 1;
> > +  /* Clear matched bits that are out of bounds. */
> > +  m = (((hm0 & hm1) >> off) << off2) >> off2;
> > +  while (m)
> > +    {
> > +      i = TZCNT (m);
> > +      m = BLSR (m);
> > +      hp = h + off + i - shift;
> > +      if (PTR_DIFF (PTR_ALIGN_UP (hp, PAGE_SIZE), hp) >= VEC_SIZE)
> > +       {
> > +         hv = LOADU ((VEC *) hp);
> > +         cmpm = (MASK) CMPEQ8_MASK (hv, nv) << matchsh;
> > +         if (cmpm == matchm)
> > +           if (ne_len <= VEC_SIZE
> > +               || !MEMCMPEQ (hp + VEC_SIZE, (const char *) ne +
> VEC_SIZE,
> > +                             ne_len - VEC_SIZE))
> > +             return (void *) hp;
> > +       }
> > +      else
> > +       {
> > +         if (!MEMCMPEQ (hp, ne, ne_len))
> > +           return (void *) hp;
> > +       }
> > +    }
> > +  h += VEC_SIZE - 1;
> > +  for (; h - shift + VEC_SIZE <= end; h += VEC_SIZE)
> > +    {
> > +      hv0 = LOADU ((const VEC *) h);
> > +      hv1 = LOAD ((const VEC *) (h + 1));
> > +      hm1 = (MASK) CMPEQ8_MASK (hv1, nv1);
> > +      hm0 = (MASK) CMPEQ8_MASK (hv0, nv0);
> > +      m = hm0 & hm1;
> > +      while (m)
> > +       {
> > +       match:
> > +         i = TZCNT (m);
> > +         m = BLSR (m);
> > +         hp = h + i - shift;
> > +         if (PTR_DIFF (PTR_ALIGN_UP (hp, PAGE_SIZE), hp) >= VEC_SIZE)
> > +           {
> > +             hv = LOADU ((VEC *) hp);
> > +             cmpm = (MASK) CMPEQ8_MASK (hv, nv) << matchsh;
> > +             if (cmpm == matchm)
> > +               if (ne_len <= VEC_SIZE
> > +                   || !MEMCMPEQ (hp + VEC_SIZE, (const char *) ne +
> VEC_SIZE,
> > +                                 ne_len - VEC_SIZE))
> > +                 return (void *) hp;
> > +           }
> > +         else
> > +           {
> > +             if (!MEMCMPEQ (hp, ne, ne_len))
> > +               return (void *) hp;
> > +           }
> > +       }
> > +    }
> > +  if (h - shift <= end)
> > +    {
> > +      off2 = VEC_SIZE - (unsigned int) (end - (h - shift)) - 1;
> > +      hv1 = LOAD ((const VEC *) (h + 1));
> > +      if (PTR_DIFF (PTR_ALIGN_UP (h, PAGE_SIZE), h) >= VEC_SIZE)
> > +       {
> > +         hv0 = LOADU ((const VEC *) h);
> > +         hm1 = (MASK) CMPEQ8_MASK (hv1, nv1);
> > +         hm0 = (MASK) CMPEQ8_MASK (hv0, nv0);
> > +       }
> > +      else
> > +       {
> > +         hm1 = (MASK) CMPEQ8_MASK (hv1, nv1);
> > +         hm0 = 1 | (MASK) CMPEQ8_MASK (hv1, nv0) << 1;
> > +       }
> > +      /* Clear matched bits that are out of bounds. */
> > +      m = ((hm0 & hm1) << off2) >> off2;
> > +      if (m)
> > +       goto match;
> > +    }
> > +  return NULL;
> > +}
>
> The implementation is ingeneral a bit hard to follow.
>
> Can you
> 1) comment the implementation. Particularly a bit lost
> following the setup code around `off`/`h`/`off2`/`shift`.
>
Comments added in v5.

> > diff --git a/sysdeps/x86_64/multiarch/memmem-avx2.c
> b/sysdeps/x86_64/multiarch/memmem-avx2.c
> > new file mode 100644
> > index 0000000000..91f5d5d331
> > --- /dev/null
> > +++ b/sysdeps/x86_64/multiarch/memmem-avx2.c
> > @@ -0,0 +1,3 @@
> > +#define FUNC_NAME __memmem_avx2
> > +
> > +#include "memmem-avx-base.h"
> > diff --git a/sysdeps/x86_64/multiarch/memmem-avx512.c
> b/sysdeps/x86_64/multiarch/memmem-avx512.c
> > new file mode 100644
> > index 0000000000..163efa2133
> > --- /dev/null
> > +++ b/sysdeps/x86_64/multiarch/memmem-avx512.c
> > @@ -0,0 +1,16 @@
> > +#define VEC __m512i
> > +#define MASK uint64_t
> > +#define LOAD(x) _mm512_load_si512 (x)
> > +#define LOADU(x) _mm512_loadu_si512 (x)
> > +#define STORE(dst, src) _mm512_store_si512 (dst, src)
> > +#define STOREU(dst, src) _mm512_storeu_si512 (dst, src)
> > +#define CMPEQ8_MASK(x, y) _mm512_cmpeq_epi8_mask (x, y)
> > +#define SETZERO(x) _mm512_setzero_si512 (x)
> > +#define SETONE8(x) _mm512_set1_epi8 (x)
> > +#define TZCNT(x) _tzcnt_u64 (x)
> > +#define BLSR(x) _blsr_u64 (x)
> > +#define ONES ((MASK) -1)
> > +
> > +#define FUNC_NAME __memmem_avx512
> > +
> > +#include "memmem-avx-base.h"
> > diff --git a/sysdeps/x86_64/multiarch/memmem.c
> b/sysdeps/x86_64/multiarch/memmem.c
> > new file mode 100644
> > index 0000000000..8fe7b77d33
> > --- /dev/null
> > +++ b/sysdeps/x86_64/multiarch/memmem.c
> > @@ -0,0 +1,67 @@
> > +/* Multiple versions of memmem.
> > +   All versions must be listed in ifunc-impl-list.c.
> > +   Copyright (C) 2012-2023 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +/* Redefine memmem so that the compiler won't complain about the type
> > +   mismatch with the IFUNC selector in strong_alias, below.  */
> > +#undef  memmem
> > +#define memmem __redirect_memmem
> > +#include <string.h>
> > +#undef  memmem
> > +
> > +#define MEMMEM __memmem_generic
> > +#ifdef SHARED
> > +# undef libc_hidden_builtin_def
> > +# define libc_hidden_builtin_def(name) \
> > +  __hidden_ver1 (__memmem_generic, __GI_memmem, __memmem_generic);
> > +#endif
> > +
> > +#include "string/memmem.c"
> > +
> > +extern __typeof (__redirect_memmem) __memmem_avx2 attribute_hidden;
> > +extern __typeof (__redirect_memmem) __memmem_generic attribute_hidden;
> > +extern __typeof (__redirect_memmem) __memmem_avx512 attribute_hidden;
> > +
> > +#define SYMBOL_NAME memmem
> > +
> > +#include "init-arch.h"
> > +
> > +/* Avoid DWARF definition DIE on ifunc symbol so that GDB can handle
> > +   ifunc symbol properly.  */
> > +extern __typeof (__redirect_memmem) __libc_memmem;
> > +
> > +static inline void *
> > +IFUNC_SELECTOR (void)
> > +{
> > +  const struct cpu_features *cpu_features = __get_cpu_features ();
> > +
> > +  if (!CPU_FEATURES_ARCH_P (cpu_features, Prefer_No_AVX512)
> > +      && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
> > +      && CPU_FEATURE_USABLE_P (cpu_features, BMI1))
> > +    return __memmem_avx512;
> > +
> > +  if (CPU_FEATURE_USABLE_P (cpu_features, AVX2)
> > +      && CPU_FEATURE_USABLE_P (cpu_features, BMI1))
> > +    return __memmem_avx2;
> > +
> > +  return __memmem_generic;
> > +}
> > +
> > +libc_ifunc_redirected (__redirect_memmem, __libc_memmem, IFUNC_SELECTOR
> ());
> > +#undef memmem
> > +strong_alias (__libc_memmem, __memmem)
> > --
> > 2.43.0
> >
>