* etc/NEWS: Update correspondingly.

* exec/Makefile.in (config-mips.m4): Don't define rule
or predicate $(LOADOBJS) on it elsewhere than on MIPS.

* exec/README: Direct developers to GDB.

* exec/trace.c (finish_exec): Resume the tracee after reporting
an error in `exec'.
(after_fork): If seccomp is enabled on Android, and the kernel
is 4.7 or earlier, detect whether revisions to the sequencing of
seccomp events have been backported from 4.8.
(exec_waitpid): Resume the process with PTRACE_CONT after
receiving an unknown signal.
(exec_init): Cease disabling seccomp on Android kernels earlier
than 4.8.

* exec/configure.ac (REENTRANT): Remove option for reentrancy.
(PROGRAM_COUNTER, HAVE_SECCOMP): Define register providing the
program counter and enable seccomp if its headers are available.

* exec/exec.c (write_load_command): Avoid defining unused
variable.
(exec_0): Remove code specific to REENTRANT configurations.

* exec/exec.h (struct exec_tracee) <exec_data, data_size>: New
fields for loader instructions and their size.

* exec/exec1.c (main): Call exec_init before forking.

* exec/mipsel-user.h (ELF_NGREG): Delete definition.
(struct mipsel_regs): Reduce number of gregs to 32, but
introduce separate fields for special registers.

* exec/trace.c (use_seccomp_p): New variable; defile to false if
!HAVE_SECCOMP.
(remove_tracee): Cease providing for non-reentrant
configurations.  Release executable data if present.
(handle_clone_prepare): Likewise.  Resume process with
PTRACE_CONT if seccomp-based interception is enabled.
(handle_clone, check_signal): Resume processes as above.
(handle_exec): Divide into two functions, with only rewriting
the system call and generating instructions for the loader
remaining in the first, and copying such instructions into the
loader's stack removed into a new function, `finish_exec'.
(finish_exec): New function.
(handle_readlinkat, handle_openat): Abolish non-REENTRANT
configurations.
(process_system_call): Divide exec system calls into two phases,
disambiguated by the value of tracee->waiting_for_syscall.  Typo
fixes.  Accommodate syscall-exit-stops where the signal was
initially intercepted by `seccomp_system_call'.
(interesting_syscalls): New array.
(ARRAYELTS): New macro.
(seccomp_system_call, establish_seccomp_filter): New function.
(tracing_execve) [HAVE_SECCOMP]: Establish a seccomp filter if
this is to be enabled.
(after_fork): Provide PTRACE_O_TRACESECCOMP.  Resume process
with PTRACE_CONT if seccomp-based interception is enabled.
(exec_waitpid): Resume process with PTRACE_CONT if seccomp-based
interception is enabled.  Dispatch stops identifying as
PTRACE_EVENT_SECCOMP to `seccomp_system_call'.
(exec_init): Establish whether it is possible to enable seccomp.

* exec/Makefile.in (is_mips): New substitution.
(.s.o): Avoid calling m4 unless it be set.

* exec/configure.ac: Substitute is_mips, and don't generate
config-mips.m4 otherwise.

* exec/loader-x86.s:

* exec/loader-x86_64.s: Use assembler rather than m4-defined
comment syntax.

* exec/configure.ac (USER_SWORD): New macro.

* exec/exec.c (format_pid): Export this function.

* exec/exec.h:

* exec/trace.c (canon_path): New function.
(handle_readlinkat, handle_openat): Test complete file name
against /proc/self/exe, and further check for /proc/pid/exe.

* exec/configure.ac (OPEN_SYSCALL, OPENAT_SYSCALL): Define new
macros.

* exec/exec.h (struct exec_tracee): New field `sp'.

* exec/trace.c (handle_openat): New function.
(process_system_call): If handle_openat executes successfully,
save the unmodified stack pointer within the tracee structure to
be restored once the system call completes.