Revert of Introduce sys_sigprocmask and sys_sigaction.

sandbox/linux/system_headers/android_x86_64_ucontext.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_X86_64_UCONTEXT_H_
+#define SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_X86_64_UCONTEXT_H_
+
+// We do something compatible with glibc. Hopefully, at some point Android will
+// provide that for us, and __BIONIC_HAVE_UCONTEXT_T should be defined.
+// Spec:
+// http://refspecs.linuxfoundation.org/LSB_4.1.0/LSB-Core-AMD64/LSB-Core-AMD64/libc-ddefs.html#AEN5668
+
+#if !defined(__BIONIC_HAVE_UCONTEXT_T)
+#include <asm/sigcontext.h>
+
+struct _libc_fpxreg {
+  unsigned short significand[4];
+  unsigned short exponent;
+  unsigned short padding[3];
+};
+
+struct _libc_xmmreg {
+  uint32_t element[4];
+};
+
+struct _libc_fpstate {
+  uint16_t cwd;
+  uint16_t swd;
+  uint16_t twd;
+  uint16_t fop;
+  uint64_t rip;
+  uint64_t rdp;
+  uint32_t mxcsr;
+  uint32_t mxcsr_mask;
+  struct _libc_fpxreg _st[8];
+  struct _libc_xmmreg _xmm[16];
+  uint32_t padding[24];
+};
+
+typedef uint64_t greg_t;
+
+typedef struct {
+  greg_t gregs[23];
+  struct _libc_fpstate* fpregs;
+  unsigned long __reserved1[8];
+} mcontext_t;
+
+enum {
+  REG_R8 = 0,
+  REG_R9,
+  REG_R10,
+  REG_R11,
+  REG_R12,
+  REG_R13,
+  REG_R14,
+  REG_R15,
+  REG_RDI,
+  REG_RSI,
+  REG_RBP,
+  REG_RBX,
+  REG_RDX,
+  REG_RAX,
+  REG_RCX,
+  REG_RSP,
+  REG_RIP,
+  REG_EFL,
+  REG_CSGSFS,
+  REG_ERR,
+  REG_TRAPNO,
+  REG_OLDMASK,
+  REG_CR2,
+  NGREG,
+};
+
+typedef struct ucontext {
+  unsigned long uc_flags;
+  struct ucontext* uc_link;
+  stack_t uc_stack;
+  mcontext_t uc_mcontext;
+  sigset_t uc_sigmask;
+  struct _libc_fpstate __fpregs_mem;
+} ucontext_t;
+
+#else
+#include <sys/ucontext.h>
+#endif  // __BIONIC_HAVE_UCONTEXT_T
+
+#endif  // SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_X86_64_UCONTEXT_H_