# \[RFC PATCH v7 4/7\] Restartable sequences: wire up ARM 32 system call

- From: Mathieu Desnoyers \<hidden\>
- Date: 2016-07-21 21:15:39 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/07/4799702
- Thread: https://ratatoskr.run/linux-api/2016/07/4799699/t.md

```text
Wire up the rseq system call on 32-bit ARM.

This provides an ABI improving the speed of a user-space getcpu
operation on ARM by skipping the getcpu system call on the fast path, as
well as improving the speed of user-space operations on per-cpu data
compared to using load-linked/store-conditional.

Signed-off-by: Mathieu Desnoyers <redacted>
CC: Russell King <redacted>
CC: Catalin Marinas <redacted>
CC: Will Deacon <redacted>
CC: Thomas Gleixner <redacted>
CC: Paul Turner <redacted>
CC: Andrew Hunter <redacted>
CC: Peter Zijlstra <redacted>
CC: Andy Lutomirski <redacted>
CC: Andi Kleen <redacted>
CC: Dave Watson <redacted>
CC: Chris Lameter <redacted>
CC: Ingo Molnar <redacted>
CC: Ben Maurer <redacted>
CC: Steven Rostedt <redacted>
CC: "Paul E. McKenney" <redacted>
CC: Josh Triplett <redacted>
CC: Linus Torvalds <redacted>
CC: Andrew Morton <redacted>
CC: Boqun Feng <redacted>
CC: <redacted>
---
 arch/arm/include/uapi/asm/unistd.h | 1 +
 arch/arm/kernel/calls.S            | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/arm/include/uapi/asm/unistd.h b/arch/arm/include/uapi/asm/unistd.h
index 2cb9dc7..8f61c79 100644
--- a/arch/arm/include/uapi/asm/unistd.h
+++ b/arch/arm/include/uapi/asm/unistd.h
@@ -420,6 +420,7 @@
 #define __NR_copy_file_range		(__NR_SYSCALL_BASE+391)
 #define __NR_preadv2			(__NR_SYSCALL_BASE+392)
 #define __NR_pwritev2			(__NR_SYSCALL_BASE+393)
+#define __NR_rseq			(__NR_SYSCALL_BASE+394)
 
 /*
  * The following SWIs are ARM private.
diff --git a/arch/arm/kernel/calls.S b/arch/arm/kernel/calls.S
index 703fa0f..0865c04 100644
--- a/arch/arm/kernel/calls.S
+++ b/arch/arm/kernel/calls.S
@@ -403,6 +403,7 @@
 		CALL(sys_copy_file_range)
 		CALL(sys_preadv2)
 		CALL(sys_pwritev2)
+		CALL(sys_rseq)
 #ifndef syscalls_counted
 .equ syscalls_padding, ((NR_syscalls + 3) & ~3) - NR_syscalls
 #define syscalls_counted
-- 
2.1.4
```