[PATCH v4] i386: Update ___tls_get_addr to preserve vector registers

[Florian Weimer]

* H. J. Lu:

> diff --git a/elf/tst-tls23.c b/elf/tst-tls23.c
> new file mode 100644
> index 0000000000..afe594c067
> --- /dev/null
> +++ b/elf/tst-tls23.c
> @@ -0,0 +1,106 @@
> +/* Test that __tls_get_addr preserves caller-saved registers.
> +   Copyright (C) 2025 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/>.  */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <dlfcn.h>
> +#include <pthread.h>
> +#include <support/xdlfcn.h>
> +#include <support/xthread.h>
> +#include <support/check.h>
> +#include <support/test-driver.h>
> +#include <tst-tls23.h>
> +
> +#ifndef IS_SUPPORTED
> +# define IS_SUPPORTED() true
> +#endif
> +
> +/* An architecture can define it to clobber caller-saved registers in
> +   malloc below to verify that __tls_get_addr won't change caller-saved
> +   registers.  */
> +#ifndef PREPARE_MALLOC
> +# define PREPARE_MALLOC()
> +#endif
> +
> +extern void * __libc_malloc (size_t);
> +
> +size_t malloc_counter = 0;
> +
> +void *
> +malloc (size_t n)
> +{
> +  PREPARE_MALLOC ();
> +  malloc_counter++;
> +  return __libc_malloc (n);
> +}
> +
> +static void *mod;
> +static const char *modname = "tst-tls23-mod.so";
> +
> +static void
> +open_mod (void)
> +{
> +  mod = xdlopen (modname, RTLD_LAZY);
> +  printf ("open %s\n", modname);
> +}
> +
> +static void
> +close_mod (void)
> +{
> +  xdlclose (mod);
> +  mod = NULL;
> +  printf ("close %s\n", modname);
> +}
> +
> +static void
> +access_mod (const char *sym)
> +{
> +  struct tls var = { -4, -4, -4, -4 };
> +  struct tls *(*f) (struct tls *) = xdlsym (mod, sym);
> +  /* Check that our malloc is called.  */
> +  malloc_counter = 0;
> +  struct tls *p = f (&var);
> +  TEST_VERIFY (malloc_counter != 0);
> +  printf ("access %s: %s() = %p\n", modname, sym, p);
> +  TEST_VERIFY_EXIT (memcmp (p, &var, sizeof (var)) == 0);
> +  ++(p->a);
> +}
> +
> +static void *
> +start (void *arg)
> +{
> +  access_mod ("apply_tls");
> +  return arg;
> +}
> +
> +static int
> +do_test (void)
> +{
> +  if (!IS_SUPPORTED ())
> +    return EXIT_UNSUPPORTED;
> +
> +  open_mod ();
> +  pthread_t t = xpthread_create (NULL, start, NULL);
> +  xpthread_join (t);
> +  close_mod ();
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>

This test fails on ppc64le because malloc_counter is not increased:

=====FAIL: elf/tst-tls23.out=====
open tst-tls23-mod.so
error: tst-tls23.c:79: not true: malloc_counter != 0
access tst-tls23-mod.so: apply_tls() = 0x7fff9f7ff980
close tst-tls23-mod.so
error: 1 test failures

This may be because of the POWER-specific __tls_get_addr_opt
optimization.

Increasing the size of TLS variables may force an allocation ppc64le as
well.

Thanks,
Florian