Re: [PATCH v2 11/19] elf: Do not duplicate the GLIBC_TUNABLES string

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

On 2023-10-17 09:05, Adhemerval Zanella wrote:
> The tunable parsing duplicates the tunable environment variable so it
> null-terminates each one since it simplifies the later parsing. It has
> the drawback of adding another point of failure (__minimal_malloc
> failing), and the memory copy requires tuning the compiler to avoid mem
> operations calls.
> 
> The parsing now tracks the tunable start and its size. The
> dl-tunable-parse.h adds helper functions to help parsing, like a strcmp
> that also checks for size and an iterator for suboptions that are
> comma-separated (used on hwcap parsing by x86, powerpc, and s390x).
> 
> Since the environment variable is allocated on the stack by the kernel,
> it is safe to keep the references to the suboptions for later parsing
> of string tunables (as done by set_hwcaps by multiple architectures).
> 
> Checked on x86_64-linux-gnu, powerpc64le-linux-gnu, and
> aarch64-linux-gnu.
> ---
>   elf/dl-tunables.c                             |  66 +++----
>   elf/dl-tunables.h                             |   6 +-
>   sysdeps/generic/dl-tunables-parse.h           | 128 ++++++++++++++
>   sysdeps/s390/cpu-features.c                   | 167 +++++++-----------
>   .../unix/sysv/linux/aarch64/cpu-features.c    |  38 ++--
>   .../unix/sysv/linux/powerpc/cpu-features.c    |  45 ++---
>   .../sysv/linux/powerpc/tst-hwcap-tunables.c   |   6 +-
>   sysdeps/x86/Makefile                          |   4 +-
>   sysdeps/x86/cpu-tunables.c                    | 118 +++++--------
>   sysdeps/x86/tst-hwcap-tunables.c              | 150 ++++++++++++++++
>   10 files changed, 455 insertions(+), 273 deletions(-)
>   create mode 100644 sysdeps/generic/dl-tunables-parse.h
>   create mode 100644 sysdeps/x86/tst-hwcap-tunables.c
> 
> diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
> index b39c14694c..869846f9da 100644
> --- a/elf/dl-tunables.c
> +++ b/elf/dl-tunables.c
> @@ -36,28 +36,6 @@
>   #define TUNABLES_INTERNAL 1
>   #include "dl-tunables.h"
>   
> -#include <not-errno.h>
> -
> -static char *
> -tunables_strdup (const char *in)
> -{
> -  size_t i = 0;
> -
> -  while (in[i++] != '\0');
> -  char *out = __minimal_malloc (i + 1);
> -
> -  /* For most of the tunables code, we ignore user errors.  However,
> -     this is a system error - and running out of memory at program
> -     startup should be reported, so we do.  */
> -  if (out == NULL)
> -    _dl_fatal_printf ("failed to allocate memory to process tunables\n");
> -
> -  while (i-- > 0)
> -    out[i] = in[i];
> -
> -  return out;
> -}
> -
>   static char **
>   get_next_env (char **envp, char **name, size_t *namelen, char **val,
>   	      char ***prev_envp)
> @@ -134,14 +112,14 @@ do_tunable_update_val (tunable_t *cur, const tunable_val_t *valp,
>   /* Validate range of the input value and initialize the tunable CUR if it looks
>      good.  */
>   static void
> -tunable_initialize (tunable_t *cur, const char *strval)
> +tunable_initialize (tunable_t *cur, const char *strval, size_t len)
>   {
> -  tunable_val_t val;
> +  tunable_val_t val = { 0 };
>   
>     if (cur->type.type_code != TUNABLE_TYPE_STRING)
>       val.numval = (tunable_num_t) _dl_strtoul (strval, NULL);
>     else
> -    val.strval = strval;
> +    val.strval = (struct tunable_str_t) { strval, len };
>     do_tunable_update_val (cur, &val, NULL, NULL);
>   }
>   
> @@ -158,29 +136,29 @@ struct tunable_toset_t
>   {
>     tunable_t *t;
>     const char *value;
> +  size_t len;
>   };
>   
>   enum { tunables_list_size = array_length (tunable_list) };
>   
>   /* Parse the tunable string VALSTRING and set TUNABLES with the found tunables
> -   and their respectibles values.  VALSTRING is a duplicated values,  where
> -   delimiters ':' are replaced with '\0', so string tunables are null
> -   terminated.
> +   and their respectibles values.  The VALSTRING is parse in place, with the

parsed

> +   tunable start and size recorded in TUNABLES.
>      Return the number of tunables found (including 0 if the string is empty)
>      or -1 if for a ill-formatted definition.  */
>   static int
> -parse_tunables_string (char *valstring, struct tunable_toset_t *tunables)
> +parse_tunables_string (const char *valstring, struct tunable_toset_t *tunables)
>   {
>     if (valstring == NULL || *valstring == '\0')
>       return 0;
>   
> -  char *p = valstring;
> +  const char *p = valstring;
>     bool done = false;
>     int ntunables = 0;
>   
>     while (!done)
>       {
> -      char *name = p;
> +      const char *name = p;
>   
>         /* First, find where the name ends.  */
>         while (*p != '=' && *p != ':' && *p != '\0')
> @@ -202,7 +180,7 @@ parse_tunables_string (char *valstring, struct tunable_toset_t *tunables)
>         /* Skip the ':' or '='.  */
>         p++;
>   
> -      char *value = p;
> +      const char *value = p;
>   
>         while (*p != '=' && *p != ':' && *p != '\0')
>   	p++;
> @@ -211,8 +189,6 @@ parse_tunables_string (char *valstring, struct tunable_toset_t *tunables)
>   	return -1;
>         else if (*p == '\0')
>   	done = true;
> -      else
> -	*p++ = '\0';
>   
>         /* Add the tunable if it exists.  */
>         for (size_t i = 0; i < tunables_list_size; i++)
> @@ -221,7 +197,8 @@ parse_tunables_string (char *valstring, struct tunable_toset_t *tunables)
>   
>   	  if (tunable_is_name (cur->name, name))
>   	    {
> -	      tunables[ntunables++] = (struct tunable_toset_t) { cur, value };
> +	      tunables[ntunables++] =
> +		(struct tunable_toset_t) { cur, value, p - value };
>   	      break;
>   	    }
>   	}
> @@ -231,7 +208,7 @@ parse_tunables_string (char *valstring, struct tunable_toset_t *tunables)
>   }
>   
>   static void
> -parse_tunables (char *valstring)
> +parse_tunables (const char *valstring)
>   {
>     struct tunable_toset_t tunables[tunables_list_size];
>     int ntunables = parse_tunables_string (valstring, tunables);
> @@ -243,7 +220,7 @@ parse_tunables (char *valstring)
>       }
>   
>     for (int i = 0; i < ntunables; i++)
> -    tunable_initialize (tunables[i].t, tunables[i].value);
> +    tunable_initialize (tunables[i].t, tunables[i].value, tunables[i].len);
>   }
>   
>   /* Initialize the tunables list from the environment.  For now we only use the
> @@ -264,9 +241,12 @@ __tunables_init (char **envp)
>     while ((envp = get_next_env (envp, &envname, &len, &envval,
>   			       &prev_envp)) != NULL)
>       {
> +      /* The environment variable is allocated on the stack by the kernel, so
> +	 it is safe to keep the references to the suboptions for later parsing
> +	 of string tunables.  */
>         if (tunable_is_name ("GLIBC_TUNABLES", envname))
>   	{
> -	  parse_tunables (tunables_strdup (envval));
> +	  parse_tunables (envval);
>   	  continue;
>   	}
>   
> @@ -284,7 +264,7 @@ __tunables_init (char **envp)
>   	  /* We have a match.  Initialize and move on to the next line.  */
>   	  if (tunable_is_name (name, envname))
>   	    {
> -	      tunable_initialize (cur, envval);
> +	      tunable_initialize (cur, envval, 0);

Do you want to put an assert in here that the env aliases are only there 
for numeric tunables?  Passing 0 does not seem right for strval tunables.

>   	      break;
>   	    }
>   	}
> @@ -298,7 +278,7 @@ __tunables_print (void)
>       {
>         const tunable_t *cur = &tunable_list[i];
>         if (cur->type.type_code == TUNABLE_TYPE_STRING
> -	  && cur->val.strval == NULL)
> +	  && cur->val.strval.str == NULL)
>   	_dl_printf ("%s:\n", cur->name);
>         else
>   	{
> @@ -324,7 +304,9 @@ __tunables_print (void)
>   			  (size_t) cur->type.max);
>   	      break;
>   	    case TUNABLE_TYPE_STRING:
> -	      _dl_printf ("%s\n", cur->val.strval);
> +	      _dl_printf ("%.*s\n",
> +			  (int) cur->val.strval.len,
> +			  cur->val.strval.str);
>   	      break;
>   	    default:
>   	      __builtin_unreachable ();
> @@ -359,7 +341,7 @@ __tunable_get_val (tunable_id_t id, void *valp, tunable_callback_t callback)
>   	}
>       case TUNABLE_TYPE_STRING:
>   	{
> -	  *((const char **)valp) = cur->val.strval;
> +	  *((struct tunable_str_t **) valp) = &cur->val.strval;
>   	  break;
>   	}
>       default:
> diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
> index 45c191e021..0e777d7d37 100644
> --- a/elf/dl-tunables.h
> +++ b/elf/dl-tunables.h
> @@ -30,7 +30,11 @@ typedef intmax_t tunable_num_t;
>   typedef union
>   {
>     tunable_num_t numval;
> -  const char *strval;
> +  struct tunable_str_t
> +  {
> +    const char *str;
> +    size_t len;
> +  } strval;
>   } tunable_val_t;
>   
>   typedef void (*tunable_callback_t) (tunable_val_t *);
> diff --git a/sysdeps/generic/dl-tunables-parse.h b/sysdeps/generic/dl-tunables-parse.h
> new file mode 100644
> index 0000000000..a2420f9129
> --- /dev/null
> +++ b/sysdeps/generic/dl-tunables-parse.h
> @@ -0,0 +1,128 @@
> +/* Helper functions to handle tunable strings.
> +   Copyright (C) 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/>.  */
> +
> +#ifndef _DL_TUNABLES_PARSE_H
> +#define _DL_TUNABLES_PARSE_H 1
> +
> +#include <string.h>
> +
> +/* Compare the contents of STRVAL with STR of size LEN.  The STR might not
> +   be null-terminated.   */
> +static __always_inline bool
> +tunable_strcmp (const struct tunable_str_t *strval, const char *str,
> +		size_t len)
> +{
> +  return strval->len == len && memcmp (strval->str, str, len) == 0;
> +}
> +#define tunable_strcmp_cte(__tunable, __str) \
> + tunable_strcmp (&__tunable->strval, __str, sizeof (__str) - 1)

What does cte stand for?

> +
> +/*
> +   Helper functions to iterate over a tunable string composed by multiple
> +   suboptions separated by comma.  Each suboptions is return in the form

Maybe enhance this comment like:

   suboptions separated by comma; this is a common pattern for CPU
   feature tunables.

Alternatively, does it make sense to treat this like a list?  That would 
make this abstraction easier to read and reason, e.g.:

   if (tunable_list_contains (&t, opt, opt1_len))
   ...
   if (tunable_list_contains_cte_any (&t, opt1, opt2, ...))

and so on.  You don't actually need the while loop or state maintenance 
then.  In fact, maybe there's a case here to make a LIST tunable type.

> +   of { address, size } (no null terminated).  For instance:
> +
> +     struct tunable_str_comma_t ts;
> +     tunable_str_comma_init (&ts, valp);
> +
> +     struct tunable_str_t t;
> +     while (tunable_str_comma_next (&ts, &t))
> +      {
> +	_dl_printf ("[%s] %.*s (%d)\n",
> +		    __func__,
> +		    (int) tstr.len,
> +		    tstr.str,
> +		    (int) tstr.len);
> +
> +        if (tunable_str_comma_strcmp (&t, opt, opt1_len))
> +	  {
> +	    [...]
> +	  }
> +	else if (tunable_str_comma_strcmp_cte (&t, "opt2"))
> +	  {
> +	    [...]
> +	  }
> +      }
> +*/
> +
> +struct tunable_str_comma_state_t
> +{
> +  const char *p;
> +  size_t plen;
> +  size_t maxplen;
> +};
> +
> +struct tunable_str_comma_t
> +{
> +  const char *str;
> +  size_t len;
> +  bool disable;
> +};
> +
> +static inline void
> +tunable_str_comma_init (struct tunable_str_comma_state_t *state,
> +			tunable_val_t *valp)
> +{
> +  state->p = valp->strval.str;
> +  state->plen = 0;
> +  state->maxplen = valp->strval.len;
> +}
> +
> +static inline bool
> +tunable_str_comma_next (struct tunable_str_comma_state_t *state,
> +			struct tunable_str_comma_t *str)
> +{
> +  if (*state->p == '\0' || state->plen >= state->maxplen)
> +    return false;
> +
> +  const char *c;
> +  for (c = state->p; *c != ','; c++, state->plen++)
> +    if (*c == '\0' || state->plen == state->maxplen)
> +      break;
> +
> +  str->str = state->p;
> +  str->len = c - state->p;
> +
> +  if (str->len > 0)
> +    {
> +      str->disable = *str->str == '-';
> +      if (str->disable)
> +	{
> +	  str->str = str->str + 1;
> +	  str->len = str->len - 1;
> +	}
> +    }
> +
> +  state->p = c + 1;
> +  state->plen++;
> +
> +  return true;
> +}
> +
> +/* Compare the contents of T with STR of size LEN.  The STR might not be
> +   null-terminated.   */
> +static __always_inline bool
> +tunable_str_comma_strcmp (const struct tunable_str_comma_t *t, const char *str,
> +			  size_t len)
> +{
> +  return t->len == len && memcmp (t->str, str, len) == 0;
> +}
> +#define tunable_str_comma_strcmp_cte(__t, __str) \
> +  tunable_str_comma_strcmp (__t, __str, sizeof (__str) - 1)
> +
> +#endif
> diff --git a/sysdeps/s390/cpu-features.c b/sysdeps/s390/cpu-features.c
> index 55449ba07f..8b1466fa7b 100644
> --- a/sysdeps/s390/cpu-features.c
> +++ b/sysdeps/s390/cpu-features.c
> @@ -22,6 +22,7 @@
>   #include <ifunc-memcmp.h>
>   #include <string.h>
>   #include <dl-symbol-redir-ifunc.h>
> +#include <dl-tunables-parse.h>
>   
>   #define S390_COPY_CPU_FEATURES(SRC_PTR, DEST_PTR)	\
>     (DEST_PTR)->hwcap = (SRC_PTR)->hwcap;			\
> @@ -51,33 +52,14 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>     struct cpu_features cpu_features_curr;
>     S390_COPY_CPU_FEATURES (cpu_features, &cpu_features_curr);
>   
> -  const char *token = valp->strval;
> -  do
> +  struct tunable_str_comma_state_t ts;
> +  tunable_str_comma_init (&ts, valp);
> +
> +  struct tunable_str_comma_t t;
> +  while (tunable_str_comma_next (&ts, &t))
>       {
> -      const char *token_end, *feature;
> -      bool disable;
> -      size_t token_len;
> -      size_t feature_len;
> -
> -      /* Find token separator or end of string.  */
> -      for (token_end = token; *token_end != ','; token_end++)
> -	if (*token_end == '\0')
> -	  break;
> -
> -      /* Determine feature.  */
> -      token_len = token_end - token;
> -      if (*token == '-')
> -	{
> -	  disable = true;
> -	  feature = token + 1;
> -	  feature_len = token_len - 1;
> -	}
> -      else
> -	{
> -	  disable = false;
> -	  feature = token;
> -	  feature_len = token_len;
> -	}
> +      if (t.len == 0)
> +	continue;
>   
>         /* Handle only the features here which are really used in the
>   	 IFUNC-resolvers.  All others are ignored as the values are only used
> @@ -85,85 +67,65 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>         bool reset_features = false;
>         unsigned long int hwcap_mask = 0UL;
>         unsigned long long stfle_bits0_mask = 0ULL;
> +      bool disable = t.disable;
>   
> -      if ((*feature == 'z' || *feature == 'a'))
> +      if (tunable_str_comma_strcmp_cte (&t, "zEC12")
> +	  || tunable_str_comma_strcmp_cte (&t, "arch10"))
> +	{
> +	  reset_features = true;
> +	  disable = true;
> +	  hwcap_mask = HWCAP_S390_VXRS | HWCAP_S390_VXRS_EXT
> +	    | HWCAP_S390_VXRS_EXT2;
> +	  stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
> +	}
> +      else if (tunable_str_comma_strcmp_cte (&t, "z13")
> +	       || tunable_str_comma_strcmp_cte (&t, "arch11"))
> +	{
> +	  reset_features = true;
> +	  disable = true;
> +	  hwcap_mask = HWCAP_S390_VXRS_EXT | HWCAP_S390_VXRS_EXT2;
> +	  stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
> +	}
> +      else if (tunable_str_comma_strcmp_cte (&t, "z14")
> +	       || tunable_str_comma_strcmp_cte (&t, "arch12"))
> +	{
> +	  reset_features = true;
> +	  disable = true;
> +	  hwcap_mask = HWCAP_S390_VXRS_EXT2;
> +	  stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
> +	}
> +      else if (tunable_str_comma_strcmp_cte (&t, "z15")
> +	       || tunable_str_comma_strcmp_cte (&t, "z16")
> +	       || tunable_str_comma_strcmp_cte (&t, "arch13")
> +	       || tunable_str_comma_strcmp_cte (&t, "arch14"))
>   	{
> -	  if ((feature_len == 5 && *feature == 'z'
> -	       && memcmp (feature, "zEC12", 5) == 0)
> -	      || (feature_len == 6 && *feature == 'a'
> -		  && memcmp (feature, "arch10", 6) == 0))
> -	    {
> -	      reset_features = true;
> -	      disable = true;
> -	      hwcap_mask = HWCAP_S390_VXRS | HWCAP_S390_VXRS_EXT
> -		| HWCAP_S390_VXRS_EXT2;
> -	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
> -	    }
> -	  else if ((feature_len == 3 && *feature == 'z'
> -		    && memcmp (feature, "z13", 3) == 0)
> -		   || (feature_len == 6 && *feature == 'a'
> -		       && memcmp (feature, "arch11", 6) == 0))
> -	    {
> -	      reset_features = true;
> -	      disable = true;
> -	      hwcap_mask = HWCAP_S390_VXRS_EXT | HWCAP_S390_VXRS_EXT2;
> -	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
> -	    }
> -	  else if ((feature_len == 3 && *feature == 'z'
> -		    && memcmp (feature, "z14", 3) == 0)
> -		   || (feature_len == 6 && *feature == 'a'
> -		       && memcmp (feature, "arch12", 6) == 0))
> -	    {
> -	      reset_features = true;
> -	      disable = true;
> -	      hwcap_mask = HWCAP_S390_VXRS_EXT2;
> -	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
> -	    }
> -	  else if ((feature_len == 3 && *feature == 'z'
> -		    && (memcmp (feature, "z15", 3) == 0
> -			|| memcmp (feature, "z16", 3) == 0))
> -		   || (feature_len == 6
> -		       && (memcmp (feature, "arch13", 6) == 0
> -			   || memcmp (feature, "arch14", 6) == 0)))
> -	    {
> -	      /* For z15 or newer we don't have to disable something,
> -		 but we have to reset to the original values.  */
> -	      reset_features = true;
> -	    }
> +	  /* For z15 or newer we don't have to disable something, but we have
> +	     to reset to the original values.  */
> +	  reset_features = true;
>   	}
> -      else if (*feature == 'H')
> +      else if (tunable_str_comma_strcmp_cte (&t, "HWCAP_S390_VXRS"))
>   	{
> -	  if (feature_len == 15
> -	      && memcmp (feature, "HWCAP_S390_VXRS", 15) == 0)
> -	    {
> -	      hwcap_mask = HWCAP_S390_VXRS;
> -	      if (disable)
> -		hwcap_mask |= HWCAP_S390_VXRS_EXT | HWCAP_S390_VXRS_EXT2;
> -	    }
> -	  else if (feature_len == 19
> -		   && memcmp (feature, "HWCAP_S390_VXRS_EXT", 19) == 0)
> -	    {
> -	      hwcap_mask = HWCAP_S390_VXRS_EXT;
> -	      if (disable)
> -		hwcap_mask |= HWCAP_S390_VXRS_EXT2;
> -	      else
> -		hwcap_mask |= HWCAP_S390_VXRS;
> -	    }
> -	  else if (feature_len == 20
> -		   && memcmp (feature, "HWCAP_S390_VXRS_EXT2", 20) == 0)
> -	    {
> -	      hwcap_mask = HWCAP_S390_VXRS_EXT2;
> -	      if (!disable)
> -		hwcap_mask |= HWCAP_S390_VXRS | HWCAP_S390_VXRS_EXT;
> -	    }
> +	  hwcap_mask = HWCAP_S390_VXRS;
> +	  if (t.disable)
> +	    hwcap_mask |= HWCAP_S390_VXRS_EXT | HWCAP_S390_VXRS_EXT2;
>   	}
> -      else if (*feature == 'S')
> +      else if (tunable_str_comma_strcmp_cte (&t, "HWCAP_S390_VXRS_EXT"))
>   	{
> -	  if (feature_len == 10
> -	      && memcmp (feature, "STFLE_MIE3", 10) == 0)
> -	    {
> -	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
> -	    }
> +	  hwcap_mask = HWCAP_S390_VXRS_EXT;
> +	  if (t.disable)
> +	    hwcap_mask |= HWCAP_S390_VXRS_EXT2;
> +	  else
> +	    hwcap_mask |= HWCAP_S390_VXRS;
> +	}
> +      else if (tunable_str_comma_strcmp_cte (&t, "HWCAP_S390_VXRS_EXT2"))
> +	{
> +	  hwcap_mask = HWCAP_S390_VXRS_EXT2;
> +	  if (!t.disable)
> +	    hwcap_mask |= HWCAP_S390_VXRS | HWCAP_S390_VXRS_EXT;
> +	}
> +      else if (tunable_str_comma_strcmp_cte (&t, "STFLE_MIE3"))
> +	{
> +	  stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
>   	}
>   
>         /* Perform the actions determined above.  */
> @@ -187,14 +149,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>   	  else
>   	    cpu_features_curr.stfle_bits[0] |= stfle_bits0_mask;
>   	}
> -
> -      /* Jump over current token ... */
> -      token += token_len;
> -
> -      /* ... and skip token separator for next round.  */
> -      if (*token == ',') token++;
>       }
> -  while (*token != '\0');
>   
>     /* Copy back the features after checking that no unsupported features were
>        enabled by user.  */
> diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> index dc09c1c827..3f1a6bcd62 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> @@ -16,10 +16,12 @@
>      License along with the GNU C Library; if not, see
>      <https://www.gnu.org/licenses/>.  */
>   
> +#include <array_length.h>
>   #include <cpu-features.h>
>   #include <sys/auxv.h>
>   #include <elf/dl-hwcaps.h>
>   #include <sys/prctl.h>
> +#include <dl-tunables-parse.h>
>   
>   #define DCZID_DZP_MASK (1 << 4)
>   #define DCZID_BS_MASK (0xf)
> @@ -33,28 +35,32 @@
>   struct cpu_list
>   {
>     const char *name;
> +  size_t len;
>     uint64_t midr;
>   };
>   
> -static struct cpu_list cpu_list[] = {
> -      {"falkor",	 0x510FC000},
> -      {"thunderxt88",	 0x430F0A10},
> -      {"thunderx2t99",   0x431F0AF0},
> -      {"thunderx2t99p1", 0x420F5160},
> -      {"phecda",	 0x680F0000},
> -      {"ares",		 0x411FD0C0},
> -      {"emag",		 0x503F0001},
> -      {"kunpeng920", 	 0x481FD010},
> -      {"a64fx",		 0x460F0010},
> -      {"generic", 	 0x0}
> +static const struct cpu_list cpu_list[] =
> +{
> +#define CPU_LIST_ENTRY(__str, __num) { __str, sizeof (__str) - 1, __num }
> +  CPU_LIST_ENTRY ("falkor",         0x510FC000),
> +  CPU_LIST_ENTRY ("thunderxt88",    0x430F0A10),
> +  CPU_LIST_ENTRY ("thunderx2t99",   0x431F0AF0),
> +  CPU_LIST_ENTRY ("thunderx2t99p1", 0x420F5160),
> +  CPU_LIST_ENTRY ("phecda",         0x680F0000),
> +  CPU_LIST_ENTRY ("ares",           0x411FD0C0),
> +  CPU_LIST_ENTRY ("emag",           0x503F0001),
> +  CPU_LIST_ENTRY ("kunpeng920",     0x481FD010),
> +  CPU_LIST_ENTRY ("a64fx",          0x460F0010),
> +  CPU_LIST_ENTRY ("generic",        0x0),
>   };
>   
>   static uint64_t
> -get_midr_from_mcpu (const char *mcpu)
> +get_midr_from_mcpu (const struct tunable_str_t *mcpu)
>   {
> -  for (int i = 0; i < sizeof (cpu_list) / sizeof (struct cpu_list); i++)
> -    if (strcmp (mcpu, cpu_list[i].name) == 0)
> +  for (int i = 0; i < array_length (cpu_list); i++) {
> +    if (tunable_strcmp (mcpu, cpu_list[i].name, cpu_list[i].len))
>         return cpu_list[i].midr;
> +  }
>   
>     return UINT64_MAX;
>   }
> @@ -65,7 +71,9 @@ init_cpu_features (struct cpu_features *cpu_features)
>     register uint64_t midr = UINT64_MAX;
>   
>     /* Get the tunable override.  */
> -  const char *mcpu = TUNABLE_GET (glibc, cpu, name, const char *, NULL);
> +  const struct tunable_str_t *mcpu = TUNABLE_GET (glibc, cpu, name,
> +						  struct tunable_str_t *,
> +						  NULL);
>     if (mcpu != NULL)
>       midr = get_midr_from_mcpu (mcpu);
>   
> diff --git a/sysdeps/unix/sysv/linux/powerpc/cpu-features.c b/sysdeps/unix/sysv/linux/powerpc/cpu-features.c
> index 7c6e20e702..390b3fd11a 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/cpu-features.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/cpu-features.c
> @@ -20,6 +20,7 @@
>   #include <stdint.h>
>   #include <cpu-features.h>
>   #include <elf/dl-tunables.h>
> +#include <dl-tunables-parse.h>
>   #include <unistd.h>
>   #include <string.h>
>   
> @@ -43,41 +44,26 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>     struct cpu_features *cpu_features = &GLRO(dl_powerpc_cpu_features);
>     unsigned long int tcbv_hwcap = cpu_features->hwcap;
>     unsigned long int tcbv_hwcap2 = cpu_features->hwcap2;
> -  const char *token = valp->strval;
> -  do
> +
> +  struct tunable_str_comma_state_t ts;
> +  tunable_str_comma_init (&ts, valp);
> +
> +  struct tunable_str_comma_t t;
> +  while (tunable_str_comma_next (&ts, &t))
>       {
> -      const char *token_end, *feature;
> -      bool disable;
> -      size_t token_len, i, feature_len, offset = 0;
> -      /* Find token separator or end of string.  */
> -      for (token_end = token; *token_end != ','; token_end++)
> -	if (*token_end == '\0')
> -	  break;
> +      if (t.len == 0)
> +	continue;
>   
> -      /* Determine feature.  */
> -      token_len = token_end - token;
> -      if (*token == '-')
> -	{
> -	  disable = true;
> -	  feature = token + 1;
> -	  feature_len = token_len - 1;
> -	}
> -      else
> -	{
> -	  disable = false;
> -	  feature = token;
> -	  feature_len = token_len;
> -	}
> -      for (i = 0; i < array_length (hwcap_tunables); ++i)
> +      size_t offset = 0;
> +      for (int i = 0; i < array_length (hwcap_tunables); ++i)
>   	{
>   	  const char *hwcap_name = hwcap_names + offset;
>   	  size_t hwcap_name_len = strlen (hwcap_name);
>   	  /* Check the tunable name on the supported list.  */
> -	  if (hwcap_name_len == feature_len
> -	      && memcmp (feature, hwcap_name, feature_len) == 0)
> +	  if (tunable_str_comma_strcmp (&t, hwcap_name, hwcap_name_len))
>   	    {
>   	      /* Update the hwcap and hwcap2 bits.  */
> -	      if (disable)
> +	      if (t.disable)
>   		{
>   		  /* Id is 1 for hwcap2 tunable.  */
>   		  if (hwcap_tunables[i].id)
> @@ -98,12 +84,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>   	    }
>   	  offset += hwcap_name_len + 1;
>   	}
> -	token += token_len;
> -	/* ... and skip token separator for next round.  */
> -	if (*token == ',')
> -	  token++;
>       }
> -  while (*token != '\0');
>   }
>   
>   static inline void
> diff --git a/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c b/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c
> index 2631016a3a..049164f841 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c
> @@ -110,7 +110,11 @@ do_test (int argc, char *argv[])
>   	run_test ("-arch_2_06", "__memcpy_power7");
>         if (hwcap & PPC_FEATURE_ARCH_2_05)
>   	run_test ("-arch_2_06,-arch_2_05","__memcpy_power6");
> -      run_test ("-arch_2_06,-arch_2_05,-power5+,-power5,-power4", "__memcpy_power4");
> +      run_test ("-arch_2_06,-arch_2_05,-power5+,-power5,-power4",
> +		"__memcpy_power4");
> +      /* Also run with valid, but empty settings.  */
> +      run_test (",-,-arch_2_06,-arch_2_05,-power5+,-power5,,-power4,-",
> +		"__memcpy_power4");
>       }
>     else
>       {
> diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
> index 917c26f116..a64e5f002a 100644
> --- a/sysdeps/x86/Makefile
> +++ b/sysdeps/x86/Makefile
> @@ -12,7 +12,8 @@ CFLAGS-get-cpuid-feature-leaf.o += $(no-stack-protector)
>   
>   tests += tst-get-cpu-features tst-get-cpu-features-static \
>   	 tst-cpu-features-cpuinfo tst-cpu-features-cpuinfo-static \
> -	 tst-cpu-features-supports tst-cpu-features-supports-static
> +	 tst-cpu-features-supports tst-cpu-features-supports-static \
> +	 tst-hwcap-tunables
>   tests-static += tst-get-cpu-features-static \
>   		tst-cpu-features-cpuinfo-static \
>   		tst-cpu-features-supports-static
> @@ -65,6 +66,7 @@ $(objpfx)tst-isa-level-1.out: $(objpfx)tst-isa-level-mod-1-baseline.so \
>   endif
>   tst-ifunc-isa-2-ENV = GLIBC_TUNABLES=glibc.cpu.hwcaps=-SSE4_2,-AVX,-AVX2,-AVX512F
>   tst-ifunc-isa-2-static-ENV = $(tst-ifunc-isa-2-ENV)
> +tst-hwcap-tunables-ARGS = -- $(host-test-program-cmd)
>   endif
>   
>   ifeq ($(subdir),math)
> diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
> index 5697885226..0608209768 100644
> --- a/sysdeps/x86/cpu-tunables.c
> +++ b/sysdeps/x86/cpu-tunables.c
> @@ -24,11 +24,12 @@
>   #include <string.h>
>   #include <cpu-features.h>
>   #include <ldsodefs.h>
> +#include <dl-tunables-parse.h>
>   #include <dl-symbol-redir-ifunc.h>
>   
>   #define CHECK_GLIBC_IFUNC_CPU_OFF(f, cpu_features, name, len)		\
>     _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
> -  if (memcmp (f, #name, len) == 0)					\
> +  if (tunable_str_comma_strcmp_cte (&f, #name))				\
>       {									\
>         CPU_FEATURE_UNSET (cpu_features, name)				\
>         break;								\
> @@ -38,7 +39,7 @@
>      which isn't available.  */
>   #define CHECK_GLIBC_IFUNC_PREFERRED_OFF(f, cpu_features, name, len)	\
>     _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
> -  if (memcmp (f, #name, len) == 0)					\
> +  if (tunable_str_comma_strcmp_cte (&f, #name) == 0)			\
>       {									\
>         cpu_features->preferred[index_arch_##name]			\
>   	&= ~bit_arch_##name;						\
> @@ -46,12 +47,11 @@
>       }
>   
>   /* Enable/disable a preferred feature NAME.  */
> -#define CHECK_GLIBC_IFUNC_PREFERRED_BOTH(f, cpu_features, name,	\
> -					  disable, len)			\
> +#define CHECK_GLIBC_IFUNC_PREFERRED_BOTH(f, cpu_features, name,	len)	\
>     _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
> -  if (memcmp (f, #name, len) == 0)					\
> +  if (tunable_str_comma_strcmp_cte (&f, #name))				\
>       {									\
> -      if (disable)							\
> +      if (f.disable)							\
>   	cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name;	\
>         else								\
>   	cpu_features->preferred[index_arch_##name] |= bit_arch_##name;	\
> @@ -61,11 +61,11 @@
>   /* Enable/disable a preferred feature NAME.  Enable a preferred feature
>      only if the feature NEED is usable.  */
>   #define CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH(f, cpu_features, name,	\
> -					       need, disable, len)	\
> +					      need, len)		\
>     _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
> -  if (memcmp (f, #name, len) == 0)					\
> +  if (tunable_str_comma_strcmp_cte (&f, #name))				\
>       {									\
> -      if (disable)							\
> +      if (f.disable)							\
>   	cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name;	\
>         else if (CPU_FEATURE_USABLE_P (cpu_features, need))		\
>   	cpu_features->preferred[index_arch_##name] |= bit_arch_##name;	\
> @@ -93,38 +93,20 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>        NOTE: the IFUNC selection may change over time.  Please check all
>        multiarch implementations when experimenting.  */
>   
> -  const char *p = valp->strval, *c;
>     struct cpu_features *cpu_features = &GLRO(dl_x86_cpu_features);
> -  size_t len;
>   
> -  do
> -    {
> -      const char *n;
> -      bool disable;
> -      size_t nl;
> -
> -      for (c = p; *c != ','; c++)
> -	if (*c == '\0')
> -	  break;
> +  struct tunable_str_comma_state_t ts;
> +  tunable_str_comma_init (&ts, valp);
>   
> -      len = c - p;
> -      disable = *p == '-';
> -      if (disable)
> -	{
> -	  n = p + 1;
> -	  nl = len - 1;
> -	}
> -      else
> -	{
> -	  n = p;
> -	  nl = len;
> -	}
> -      switch (nl)
> +  struct tunable_str_comma_t n;
> +  while (tunable_str_comma_next (&ts, &n))
> +    {
> +      switch (n.len)
>   	{
>   	default:
>   	  break;
>   	case 3:
> -	  if (disable)
> +	  if (n.disable)
>   	    {
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX, 3);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, CX8, 3);
> @@ -135,7 +117,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>   	    }
>   	  break;
>   	case 4:
> -	  if (disable)
> +	  if (n.disable)
>   	    {
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX2, 4);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, BMI1, 4);
> @@ -149,7 +131,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>   	    }
>   	  break;
>   	case 5:
> -	  if (disable)
> +	  if (n.disable)
>   	    {
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, LZCNT, 5);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, MOVBE, 5);
> @@ -159,12 +141,12 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>   	    }
>   	  break;
>   	case 6:
> -	  if (disable)
> +	  if (n.disable)
>   	    {
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, POPCNT, 6);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_1, 6);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_2, 6);
> -	      if (memcmp (n, "XSAVEC", 6) == 0)
> +	      if (memcmp (n.str, "XSAVEC", 6) == 0)
>   		{
>   		  /* Update xsave_state_size to XSAVE state size.  */
>   		  cpu_features->xsave_state_size
> @@ -174,14 +156,14 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>   	    }
>   	  break;
>   	case 7:
> -	  if (disable)
> +	  if (n.disable)
>   	    {
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512F, 7);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, OSXSAVE, 7);
>   	    }
>   	  break;
>   	case 8:
> -	  if (disable)
> +	  if (n.disable)
>   	    {
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512CD, 8);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512BW, 8);
> @@ -190,86 +172,72 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512PF, 8);
>   	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512VL, 8);
>   	    }
> -	  CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Slow_BSF,
> -					    disable, 8);
> +	  CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Slow_BSF, 8);
>   	  break;
>   	case 11:
>   	    {
> -	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
> -						Prefer_ERMS,
> -						disable, 11);
> -	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
> -						Prefer_FSRM,
> -						disable, 11);
> +	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Prefer_ERMS,
> +						11);
> +	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Prefer_FSRM,
> +						11);
>   	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH (n, cpu_features,
>   						     Slow_SSE4_2,
>   						     SSE4_2,
> -						     disable, 11);
> +						     11);
>   	    }
>   	  break;
>   	case 15:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
> -						Fast_Rep_String,
> -						disable, 15);
> +						Fast_Rep_String, 15);
>   	    }
>   	  break;
>   	case 16:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
> -		(n, cpu_features, Prefer_No_AVX512, AVX512F,
> -		 disable, 16);
> +		(n, cpu_features, Prefer_No_AVX512, AVX512F, 16);
>   	    }
>   	  break;
>   	case 18:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
> -						Fast_Copy_Backward,
> -						disable, 18);
> +						Fast_Copy_Backward, 18);
>   	    }
>   	  break;
>   	case 19:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
> -						Fast_Unaligned_Load,
> -						disable, 19);
> +						Fast_Unaligned_Load, 19);
>   	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
> -						Fast_Unaligned_Copy,
> -						disable, 19);
> +						Fast_Unaligned_Copy, 19);
>   	    }
>   	  break;
>   	case 20:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
> -		(n, cpu_features, Prefer_No_VZEROUPPER, AVX, disable,
> -		 20);
> +		(n, cpu_features, Prefer_No_VZEROUPPER, AVX, 20);
>   	    }
>   	  break;
>   	case 23:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
> -		(n, cpu_features, AVX_Fast_Unaligned_Load, AVX,
> -		 disable, 23);
> +		(n, cpu_features, AVX_Fast_Unaligned_Load, AVX, 23);
>   	    }
>   	  break;
>   	case 24:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
> -		(n, cpu_features, MathVec_Prefer_No_AVX512, AVX512F,
> -		 disable, 24);
> +		(n, cpu_features, MathVec_Prefer_No_AVX512, AVX512F, 24);
>   	    }
>   	  break;
>   	case 26:
>   	    {
>   	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
> -		(n, cpu_features, Prefer_PMINUB_for_stringop, SSE2,
> -		 disable, 26);
> +		(n, cpu_features, Prefer_PMINUB_for_stringop, SSE2, 26);
>   	    }
>   	  break;
>   	}
> -      p += len + 1;
>       }
> -  while (*c != '\0');
>   }
>   
>   #if CET_ENABLED
> @@ -277,11 +245,11 @@ attribute_hidden
>   void
>   TUNABLE_CALLBACK (set_x86_ibt) (tunable_val_t *valp)
>   {
> -  if (memcmp (valp->strval, "on", sizeof ("on")) == 0)
> +  if (tunable_strcmp_cte (valp, "on"))
>       GL(dl_x86_feature_control).ibt = cet_always_on;
> -  else if (memcmp (valp->strval, "off", sizeof ("off")) == 0)
> +  else if (tunable_strcmp_cte (valp, "off"))
>       GL(dl_x86_feature_control).ibt = cet_always_off;
> -  else if (memcmp (valp->strval, "permissive", sizeof ("permissive")) == 0)
> +  else if (tunable_strcmp_cte (valp, "permissive"))
>       GL(dl_x86_feature_control).ibt = cet_permissive;
>   }
>   
> @@ -289,11 +257,11 @@ attribute_hidden
>   void
>   TUNABLE_CALLBACK (set_x86_shstk) (tunable_val_t *valp)
>   {
> -  if (memcmp (valp->strval, "on", sizeof ("on")) == 0)
> +  if (tunable_strcmp_cte (valp, "on"))
>       GL(dl_x86_feature_control).shstk = cet_always_on;
> -  else if (memcmp (valp->strval, "off", sizeof ("off")) == 0)
> +  else if (tunable_strcmp_cte (valp, "off"))
>       GL(dl_x86_feature_control).shstk = cet_always_off;
> -  else if (memcmp (valp->strval, "permissive", sizeof ("permissive")) == 0)
> +  else if (tunable_strcmp_cte (valp, "permissive"))
>       GL(dl_x86_feature_control).shstk = cet_permissive;
>   }
>   #endif
> diff --git a/sysdeps/x86/tst-hwcap-tunables.c b/sysdeps/x86/tst-hwcap-tunables.c
> new file mode 100644
> index 0000000000..e9f50ffbe0
> --- /dev/null
> +++ b/sysdeps/x86/tst-hwcap-tunables.c
> @@ -0,0 +1,150 @@
> +/* Tests for powerpc GLIBC_TUNABLES=glibc.cpu.hwcaps filter.
> +   Copyright (C) 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
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#pragma GCC optimize ("O0")
> +
> +#include <array_length.h>
> +#include <getopt.h>
> +#include <ifunc-impl-list.h>
> +#include <spawn.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <intprops.h>
> +#include <support/check.h>
> +#include <support/support.h>
> +#include <support/xunistd.h>
> +#include <support/capture_subprocess.h>
> +
> +/* Nonzero if the program gets called via `exec'.  */
> +#define CMDLINE_OPTIONS \
> +  { "restart", no_argument, &restart, 1 },
> +static int restart;
> +
> +/* Disable everything.  */
> +static const char *test_1[] =
> +{
> +  "__memcpy_avx512_no_vzeroupper",
> +  "__memcpy_avx512_unaligned",
> +  "__memcpy_avx512_unaligned_erms",
> +  "__memcpy_evex_unaligned",
> +  "__memcpy_evex_unaligned_erms",
> +  "__memcpy_avx_unaligned",
> +  "__memcpy_avx_unaligned_erms",
> +  "__memcpy_avx_unaligned_rtm",
> +  "__memcpy_avx_unaligned_erms_rtm",
> +  "__memcpy_ssse3",
> +};
> +
> +static const struct test_t
> +{
> +  const char *env;
> +  const char *const *funcs;
> +  size_t nfuncs;
> +} tests[] =
> +{
> +  {
> +    /* Disable everything.  */
> +    "-Prefer_ERMS,-Prefer_FSRM,-AVX,-AVX2,-AVX_Usable,-AVX2_Usable,"
> +    "-AVX512F_Usable,-SSE4_1,-SSE4_2,-SSSE3,-Fast_Unaligned_Load,-ERMS,"
> +    "-AVX_Fast_Unaligned_Load",
> +    test_1,
> +    array_length (test_1)
> +  },
> +  {
> +    /* Same as before, but with some empty suboptions.  */
> +    ",-,-Prefer_ERMS,-Prefer_FSRM,-AVX,-AVX2,-AVX_Usable,-AVX2_Usable,"
> +    "-AVX512F_Usable,-SSE4_1,-SSE4_2,,-SSSE3,-Fast_Unaligned_Load,,-,-ERMS,"
> +    "-AVX_Fast_Unaligned_Load,-,",
> +    test_1,
> +    array_length (test_1)
> +  }
> +};
> +
> +/* Called on process re-execution.  */
> +_Noreturn static void
> +handle_restart (int ntest)
> +{
> +  struct libc_ifunc_impl impls[32];
> +  int cnt = __libc_ifunc_impl_list ("memcpy", impls, array_length (impls));
> +  if (cnt == 0)
> +    _exit (EXIT_SUCCESS);
> +  TEST_VERIFY_EXIT (cnt >= 1);
> +  for (int i = 0; i < cnt; i++)
> +    {
> +      for (int f = 0; f < tests[ntest].nfuncs; f++)
> +	{
> +	  if (strcmp (impls[i].name, tests[ntest].funcs[f]) == 0)
> +	    TEST_COMPARE (impls[i].usable, false);
> +	}
> +    }
> +
> +  _exit (EXIT_SUCCESS);
> +}
> +
> +static int
> +do_test (int argc, char *argv[])
> +{
> +  /* We must have either:
> +     - One our fource parameters left if called initially:
> +       + path to ld.so         optional
> +       + "--library-path"      optional
> +       + the library path      optional
> +       + the application name
> +       + the test to check  */
> +
> +  TEST_VERIFY_EXIT (argc == 2 || argc == 5);
> +
> +  if (restart)
> +    handle_restart (atoi (argv[1]));
> +
> +  char nteststr[INT_BUFSIZE_BOUND (int)];
> +
> +  char *spargv[10];
> +  {
> +    int i = 0;
> +    for (; i < argc - 1; i++)
> +      spargv[i] = argv[i + 1];
> +    spargv[i++] = (char *) "--direct";
> +    spargv[i++] = (char *) "--restart";
> +    spargv[i++] = nteststr;
> +    spargv[i] = NULL;
> +  }
> +
> +  for (int i = 0; i < array_length (tests); i++)
> +    {
> +      snprintf (nteststr, sizeof nteststr, "%d", i);
> +
> +      printf ("[%d] Spawned test for %s\n", i, tests[i].env);
> +      char *tunable = xasprintf ("glibc.cpu.hwcaps=%s", tests[i].env);
> +      setenv ("GLIBC_TUNABLES", tunable, 1);
> +
> +      struct support_capture_subprocess result
> +	= support_capture_subprogram (spargv[0], spargv);
> +      support_capture_subprocess_check (&result, "tst-tunables", 0,
> +					sc_allow_stderr);
> +      support_capture_subprocess_free (&result);
> +
> +      free (tunable);
> +    }
> +
> +  return 0;
> +}
> +
> +#define TEST_FUNCTION_ARGV do_test
> +#include <support/test-driver.c>