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

[H.J. Lu]

On Tue, Jun 17, 2025 at 7:46 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * 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.

Can you find out what size should be?

> Thanks,
> Florian
>


-- 
H.J.