diff mbox series

[v3] nptl: Add <thread_pointer.h> for RISC-V

Message ID 20241015185225.1204426-1-mjeanson@efficios.com
State New
Headers show
Series [v3] nptl: Add <thread_pointer.h> for RISC-V | expand

Commit Message

Michael Jeanson Oct. 15, 2024, 6:52 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.

In the fallback code, reuse '__thread_self' from 'tls.h' as GCC doesn't
accept multiple global register variables for the same register.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
---
Changes since v2:
- The 'register' variable has to be global to generate the correct asm
- Reuse '__thread_self' from 'tls.h'
Changes since v1:
- Use __glibc_has_builtin instead of GCC version check
- Use 'register' variable instead of inline asm
---
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Darius Rad <darius@bluespec.com>
Cc: Jeff Law <jeffreyalaw@gmail.com>
---
 sysdeps/riscv/nptl/thread_pointer.h | 40 +++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 sysdeps/riscv/nptl/thread_pointer.h

Comments

Florian Weimer Oct. 15, 2024, 8 p.m. UTC | #1 
* Michael Jeanson:

> - Reuse '__thread_self' from 'tls.h'

Sorry, this is not possible because <tls.h> is not an installed
header.
Michael Jeanson Oct. 15, 2024, 8:30 p.m. UTC | #2 
On 2024-10-15 22:00, Florian Weimer wrote:
> * Michael Jeanson:
> 
>> - Reuse '__thread_self' from 'tls.h'
> 
> Sorry, this is not possible because <tls.h> is not an installed
> header.

Hum,  I suppose we could revert to the inline assembly for the fallback
code since gcc won't allow multiple global register variables for the
same register.
Florian Weimer Oct. 15, 2024, 8:35 p.m. UTC | #3 
* Michael Jeanson:

> On 2024-10-15 22:00, Florian Weimer wrote:
>> * Michael Jeanson:
>> 
>>> - Reuse '__thread_self' from 'tls.h'
>> 
>> Sorry, this is not possible because <tls.h> is not an installed
>> header.
>
> Hum,  I suppose we could revert to the inline assembly for the fallback
> code since gcc won't allow multiple global register variables for the
> same register.

Oh, good point.  So inline assembly it is.
diff mbox series

Patch

diff --git a/sysdeps/riscv/nptl/thread_pointer.h b/sysdeps/riscv/nptl/thread_pointer.h
new file mode 100644
index 0000000000..77b537fda0
--- /dev/null
+++ b/sysdeps/riscv/nptl/thread_pointer.h
@@ -0,0 +1,40 @@ 
+/* __thread_pointer definition.  riscv 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>
+
+#if __glibc_has_builtin (__builtin_thread_pointer)
+static inline void *
+__thread_pointer (void)
+{
+  return __builtin_thread_pointer ();
+}
+#else
+#include <tls.h>
+
+static inline void *
+__thread_pointer (void)
+{
+  return __thread_self;
+}
+#endif
+
+#endif /* _SYS_THREAD_POINTER_H */