[PATCH v2 17/21] nptl: nios2: Fix Race conditions in pthread cancellation (BZ#12683)

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

This patch adds the nios2 modifications required for the BZ#12683.
It basically adds the required ucontext_get_pc function.

The default syscall_cancel.c should be as expected for NIOS2. With
GCC 6.2.1 syscall_cancel.c generates the following code:

---
00000000 <__GI___syscall_cancel_arch>:
   0:   defffe04        addi    sp,sp,-8
   4:   dd800015        stw     r22,0(sp)
   8:   002ce03a        nextpc  r22
   c:   02000034        movhi   r8,0
  10:   42000004        addi    r8,r8,0
  14:   dfc00115        stw     ra,4(sp)
  18:   b22d883a        add     r22,r22,r8

0000001c <__syscall_cancel_arch_start>:
  1c:   20c00017        ldw     r3,0(r4)
  20:   18c0010c        andi    r3,r3,4
  24:   18000f1e        bne     r3,zero,64 <__syscall_cancel_arch_end+0x18>
  28:   3015883a        mov     r10,r6
  2c:   2805883a        mov     r2,r5
  30:   da400517        ldw     r9,20(sp)
  34:   380b883a        mov     r5,r7
  38:   da000417        ldw     r8,16(sp)
  3c:   d9c00317        ldw     r7,12(sp)
  40:   d9800217        ldw     r6,8(sp)
  44:   5009883a        mov     r4,r10
  48:   003b683a        trap    0

0000004c <__syscall_cancel_arch_end>:
  4c:   38000126        beq     r7,zero,54 <__syscall_cancel_arch_end+0x8>
  50:   0085c83a        sub     r2,zero,r2
  54:   dfc00117        ldw     ra,4(sp)
  58:   dd800017        ldw     r22,0(sp)
  5c:   dec00204        addi    sp,sp,8
  60:   f800283a        ret
  64:   b0800017        ldw     r2,0(r22)
  68:   103ee83a        callr   r2
---

Checked against a build and make check run-built-tests=no for
nios2-linux-gnu.

	[BZ #12683]
	* sysdeps/unix/sysv/linux/nios2/sigcontextinfo.h (ucontext_get_pc):
	New function.
---
 ChangeLog                                      |  4 ++++
 sysdeps/unix/sysv/linux/nios2/sigcontextinfo.h | 16 ++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/nios2/sigcontextinfo.h b/sysdeps/unix/sysv/linux/nios2/sigcontextinfo.h
index 57b9b50..7ae735f 100644
--- a/sysdeps/unix/sysv/linux/nios2/sigcontextinfo.h
+++ b/sysdeps/unix/sysv/linux/nios2/sigcontextinfo.h
@@ -16,6 +16,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#ifndef _SIGCONTEXTINFO_H
+#define _SIGCONTEXTINFO_H
+
+#include <stdint.h>
+
 #include <sys/ucontext.h>
 #include "kernel-features.h"
 
@@ -33,3 +38,14 @@
   (act)->sa_flags |= SA_SIGINFO; \
   (sigaction) (sig, act, oact); \
 })
+
+static inline uintptr_t
+ucontext_get_pc (const ucontext_t *uc)
+{
+  /* rt_restore_ucontext (arch/nios/kernel/signal.c) sets this position
+     to 'ea' register which is stated as exception return address (pc)
+     at arch/nios2/include/asm/ptrace.h.  */
+  return uc->uc_mcontext.regs[27];
+}
+
+#endif /* _SIGCONTEXTINFO_H  */
-- 
2.7.4