title: Valgrind `Unsupported arch_prctl option`
body: <p>I have a program that I know has some weird memory issues going on, so I turned to Valgrind. However, I am getting the following mysterious output:</p>
  
  <pre><code>==32006== Memcheck, a memory error detector
  ==32006== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
  ==32006== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
  ==32006== Command: ./012
  ==32006== Parent PID: 29454
  ==32006== 
  
  valgrind: the 'impossible' happened:
     Unsupported arch_prctl option
  
  host stacktrace:
  ==32006==    at 0x580441BA: show_sched_status_wrk (m_libcassert.c:355)
  ==32006==    by 0x580442D4: report_and_quit (m_libcassert.c:426)
  ==32006==    by 0x58044517: panic (m_libcassert.c:502)
  ==32006==    by 0x58044517: vgPlain_core_panic_at (m_libcassert.c:507)
  ==32006==    by 0x5804454A: vgPlain_core_panic (m_libcassert.c:512)
  ==32006==    by 0x580DAE22: vgSysWrap_amd64_linux_sys_arch_prctl_before (syswrap-amd64-linux.c:286)
  ==32006==    by 0x580A0C23: vgPlain_client_syscall (syswrap-main.c:1857)
  ==32006==    by 0x5809D48A: handle_syscall (scheduler.c:1126)
  ==32006==    by 0x5809EBB6: vgPlain_scheduler (scheduler.c:1443)
  ==32006==    by 0x580AED50: thread_wrapper (syswrap-linux.c:103)
  ==32006==    by 0x580AED50: run_a_thread_NORETURN (syswrap-linux.c:156)
  
  sched status:
    running_tid=1
  
  Thread 1: status = VgTs_Runnable (lwpid 32006)
  ==32006==    at 0x401A1C5: ??? (in /usr/lib/ld-2.28.so)
  ==32006==    by 0xBFEBFBFE: ???
  
  
  Note: see also the FAQ in the source distribution.
  It contains workarounds to several common problems.
  In particular, if Valgrind aborted or crashed after
  identifying problems in your program, there's a good chance
  that fixing those problems will prevent Valgrind aborting or
  crashing, especially if it happened in m_mallocfree.c.
  
  If that doesn't help, please report this bug to: www.valgrind.org
  
  In the bug report, send all the above text, the valgrind
  version, and what OS and version you are using.  Thanks.
  </code></pre>
  
  <p>The original bug I am trying to diagnose occurs when I am trying to insert <code>uint64_t</code>s into a <code>std::set</code> based on values in a <code>std::vector</code> (not a pointer in sight).</p>