[glibc/azanella/bz12683] nptl: aarch64: Fix Race conditions in pthread cancellation [BZ#12683]

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=091ffe8f60115932096bd1d4b7378a75d95f1caf

commit 091ffe8f60115932096bd1d4b7378a75d95f1caf
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Mon Jan 7 16:03:04 2019 +0000

    nptl: aarch64: Fix Race conditions in pthread cancellation [BZ#12683]
    
    This patch adds the aarch64 modifications required for the BZ#12683 fix
    by adding the arch-specific cancellation syscall bridge.
    
    Checked on aarch64-linux-gnu.

Diff:
---
 sysdeps/aarch64/nptl/tcb-offsets.sym             |  3 ++
 sysdeps/unix/sysv/linux/aarch64/syscall_cancel.S | 59 ++++++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/sysdeps/aarch64/nptl/tcb-offsets.sym b/sysdeps/aarch64/nptl/tcb-offsets.sym
index 238647dd47..614ea23034 100644
--- a/sysdeps/aarch64/nptl/tcb-offsets.sym
+++ b/sysdeps/aarch64/nptl/tcb-offsets.sym
@@ -4,3 +4,6 @@
 PTHREAD_MULTIPLE_THREADS_OFFSET		offsetof (struct pthread, header.multiple_threads)
 PTHREAD_TID_OFFSET			offsetof (struct pthread, tid)
 PTHREAD_SIZEOF				sizeof (struct pthread)
+
+-- Not strictly offsets, used on syscall_cancel.S
+TCB_CANCELED_BIT			CANCELED_BIT
diff --git a/sysdeps/unix/sysv/linux/aarch64/syscall_cancel.S b/sysdeps/unix/sysv/linux/aarch64/syscall_cancel.S
new file mode 100644
index 0000000000..fcb7cf66bf
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/aarch64/syscall_cancel.S
@@ -0,0 +1,59 @@
+/* Cancellable syscall wrapper.  Linux/AArch64 version.
+   Copyright (C) 2020 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 <sysdep.h>
+
+/* long int [r0] __syscall_cancel_arch (int *cancelhandling [r0],
+					long int nr   [r1],
+					long int arg1 [r2],
+					long int arg2 [r3],
+					long int arg3 [SP],
+					long int arg4 [SP+4],
+					long int arg5 [SP+8],
+					long int arg6 [SP+12])  */
+
+ENTRY (__syscall_cancel_arch)
+
+	.globl __syscall_cancel_arch_start
+__syscall_cancel_arch_start:
+
+	/* if (*cancelhandling & CANCELED_BITMASK)
+	     __syscall_do_cancel()  */
+	ldr	w0, [x0]
+	tbnz    w0, TCB_CANCELED_BIT, 1f
+
+	/* Issue a 6 argument syscall, the nr [x1] being the syscall
+	   number.  */
+	mov	x8, x1
+	mov	x0, x2
+	mov	x1, x3
+	mov	x2, x4
+	mov	x3, x5
+	mov	x4, x6
+	mov	x5, x7
+	svc	0x0
+
+	.globl __syscall_cancel_arch_end
+__syscall_cancel_arch_end:
+	ret
+
+1:
+	b	__syscall_do_cancel
+
+END (__syscall_cancel_arch)
+libc_hidden_def (__syscall_cancel_arch)