nptl: Add <thread_pointer.h> for sparc

Message ID 20241023211023.576959-1-mjeanson@efficios.com
State Superseded, archived
Delegated to: Arjun Shankar
Headers
Series nptl: Add <thread_pointer.h> for sparc |

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Commit Message

Michael Jeanson Oct. 23, 2024, 9:10 p.m. UTC
  This will be required by the rseq extensible ABI implementation on all
Linux architectures exposing the '__rseq_size' and '__rseq_offset'
symbols to set the initial value of the 'cpu_id' field which can be used
by applications to test if rseq is available and registered. As long as
the symbols are exposed it is valid for an application to perform this
test even if rseq is not yet implemented in libc for this architecture.

Both code paths are compile tested with build-many-glibcs.py but I don't
have access to any hardware to run the tests.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
---
Cc: Florian Weimer <fweimer@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Andreas K. Hüttel <dilfridge@gentoo.org>
---
 sysdeps/sparc/nptl/thread_pointer.h | 36 +++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 sysdeps/sparc/nptl/thread_pointer.h
  

Comments

Arjun Shankar Oct. 30, 2024, 3:15 p.m. UTC | #1
Hi Michael,

> This will be required by the rseq extensible ABI implementation on all
> Linux architectures exposing the '__rseq_size' and '__rseq_offset'
> symbols to set the initial value of the 'cpu_id' field which can be used
> by applications to test if rseq is available and registered. As long as
> the symbols are exposed it is valid for an application to perform this
> test even if rseq is not yet implemented in libc for this architecture.
>
> Both code paths are compile tested with build-many-glibcs.py but I don't
> have access to any hardware to run the tests.
>
> Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
> ---
> Cc: Florian Weimer <fweimer@redhat.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
> Cc: Andreas K. Hüttel <dilfridge@gentoo.org>

Again, reviewing this for being reasonable. I don't have access to the
hardware either. build-many-glibcs passes.

Reviewed-by: Arjun Shankar <arjun@redhat.com>

> ---
>  sysdeps/sparc/nptl/thread_pointer.h | 36 +++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100644 sysdeps/sparc/nptl/thread_pointer.h
>
> diff --git a/sysdeps/sparc/nptl/thread_pointer.h b/sysdeps/sparc/nptl/thread_pointer.h
> new file mode 100644
> index 0000000000..76a666e586
> --- /dev/null
> +++ b/sysdeps/sparc/nptl/thread_pointer.h

OK. Good file location and name.

> @@ -0,0 +1,36 @@
> +/* __thread_pointer definition.  sparc version.
> +   Copyright (C) 2021-2024 Free Software Foundation, Inc.

OK. This is a modified copy of another thread_pointer.h file with the
same copyright line.

> +   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 _SYS_THREAD_POINTER_H
> +#define _SYS_THREAD_POINTER_H

OK.

> +
> +#include <sys/cdefs.h>

OK. Needed for glibc_has_builtin.

> +
> +static inline void *
> +__thread_pointer (void)
> +{
> +#if __glibc_has_builtin (__builtin_thread_pointer)
> +  return __builtin_thread_pointer ();
> +#else
> +  void *__thread_register;
> +  __asm__ ("mov %%g7, %0" : "=r" (__thread_register));
> +  return __thread_register;
> +#endif

OK. Use the builtin if it exists, otherwise emit assembly. I can't
verify if it's correct but build-many-glibcs passed.

> +}
> +
> +#endif /* _SYS_THREAD_POINTER_H */

OK.

> --
> 2.43.0
>
  
John Paul Adrian Glaubitz Oct. 30, 2024, 3:20 p.m. UTC | #2
Hi Arjun,

On Wed, 2024-10-30 at 16:15 +0100, Arjun Shankar wrote:
> Hi Michael,
> 
> > This will be required by the rseq extensible ABI implementation on all
> > Linux architectures exposing the '__rseq_size' and '__rseq_offset'
> > symbols to set the initial value of the 'cpu_id' field which can be used
> > by applications to test if rseq is available and registered. As long as
> > the symbols are exposed it is valid for an application to perform this
> > test even if rseq is not yet implemented in libc for this architecture.
> > 
> > Both code paths are compile tested with build-many-glibcs.py but I don't
> > have access to any hardware to run the tests.
> > 
> > Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
> > ---
> > Cc: Florian Weimer <fweimer@redhat.com>
> > Cc: David S. Miller <davem@davemloft.net>
> > Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
> > Cc: Andreas K. Hüttel <dilfridge@gentoo.org>
> 
> Again, reviewing this for being reasonable. I don't have access to the
> hardware either. build-many-glibcs passes.
> 
> Reviewed-by: Arjun Shankar <arjun@redhat.com>

Adhemerval (CC'ed) has hardware access for Linux on SPARC. Maybe he can test the patch.

A new Linux on SPARC machine is in the works for the compile farm in the meantime.

Sorry for the unavailability.

Adrian
  
Adhemerval Zanella Netto Oct. 30, 2024, 8:21 p.m. UTC | #3
On 23/10/24 18:10, Michael Jeanson wrote:
> This will be required by the rseq extensible ABI implementation on all
> Linux architectures exposing the '__rseq_size' and '__rseq_offset'
> symbols to set the initial value of the 'cpu_id' field which can be used
> by applications to test if rseq is available and registered. As long as
> the symbols are exposed it is valid for an application to perform this
> test even if rseq is not yet implemented in libc for this architecture.
> 
> Both code paths are compile tested with build-many-glibcs.py but I don't
> have access to any hardware to run the tests.
> 
> Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
> ---
> Cc: Florian Weimer <fweimer@redhat.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
> Cc: Andreas K. Hüttel <dilfridge@gentoo.org>
> ---
>  sysdeps/sparc/nptl/thread_pointer.h | 36 +++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100644 sysdeps/sparc/nptl/thread_pointer.h
> 
> diff --git a/sysdeps/sparc/nptl/thread_pointer.h b/sysdeps/sparc/nptl/thread_pointer.h
> new file mode 100644
> index 0000000000..76a666e586
> --- /dev/null
> +++ b/sysdeps/sparc/nptl/thread_pointer.h
> @@ -0,0 +1,36 @@
> +/* __thread_pointer definition.  sparc version.
> +   Copyright (C) 2021-2024 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 _SYS_THREAD_POINTER_H
> +#define _SYS_THREAD_POINTER_H
> +
> +#include <sys/cdefs.h>
> +
> +static inline void *
> +__thread_pointer (void)
> +{
> +#if __glibc_has_builtin (__builtin_thread_pointer)
> +  return __builtin_thread_pointer ();
> +#else

It does not seems to work on all gcc versions, with the testcase:

$ cat t.c
#include <sys/cdefs.h>

void *__thread_pointer (void)
{
#if __glibc_has_builtin (__builtin_thread_pointer)
  return __builtin_thread_pointer ();
#else
  void *__thread_register;
  __asm__ ("mov %%g7, %0" : "=r" (__thread_register));
  return __thread_register;
#endif
}

$ sparc64-glibc-linux-gnu-gcc -v 2>&1 | grep version
gcc version 14.2.1 20241007 [releases/gcc-14 r14-10750-g4af44f2cf7d] (GCC)

$ sparc64-glibc-linux-gnu-gcc t.c -S -o -
        .file   "t.c"
        .section        ".text"
t.c: In function ‘__thread_pointer’:
t.c:6:10: error: ‘__builtin_thread_pointer’ is not supported on this target
    6 |   return __builtin_thread_pointer ();
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~

> +  void *__thread_register;
> +  __asm__ ("mov %%g7, %0" : "=r" (__thread_register));
> +  return __thread_register;
> +#endif
> +}
> +
> +#endif /* _SYS_THREAD_POINTER_H */
  

Patch

diff --git a/sysdeps/sparc/nptl/thread_pointer.h b/sysdeps/sparc/nptl/thread_pointer.h
new file mode 100644
index 0000000000..76a666e586
--- /dev/null
+++ b/sysdeps/sparc/nptl/thread_pointer.h
@@ -0,0 +1,36 @@ 
+/* __thread_pointer definition.  sparc version.
+   Copyright (C) 2021-2024 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 _SYS_THREAD_POINTER_H
+#define _SYS_THREAD_POINTER_H
+
+#include <sys/cdefs.h>
+
+static inline void *
+__thread_pointer (void)
+{
+#if __glibc_has_builtin (__builtin_thread_pointer)
+  return __builtin_thread_pointer ();
+#else
+  void *__thread_register;
+  __asm__ ("mov %%g7, %0" : "=r" (__thread_register));
+  return __thread_register;
+#endif
+}
+
+#endif /* _SYS_THREAD_POINTER_H */