--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc

+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc

@@ -57,6 +57,14 @@

 #include "sanitizer_mutex.h"

 #include "sanitizer_placement_new.h"

+// Sufficiently old kernel headers don't provide this value, but we can still

+// call prctl with it. If the runtime kernel is new enough, the prctl call will

+// have the desired effect; if the kernel is too old, the call will error and we

+// can ignore said error.

+#ifndef PR_SET_PTRACER

+#define PR_SET_PTRACER 0x59616d61

+#endif

+

 // This module works by spawning a Linux task which then attaches to every

 // thread in the caller process with ptrace. This suspends the threads, and

 // PTRACE_GETREGS can then be used to obtain their register state. The callback

@@ -433,9 +441,7 @@

     ScopedSetTracerPID scoped_set_tracer_pid(tracer_pid);

     // On some systems we have to explicitly declare that we want to be traced

     // by the tracer thread.

-#ifdef PR_SET_PTRACER

     internal_prctl(PR_SET_PTRACER, tracer_pid, 0, 0, 0);

-#endif

     // Allow the tracer thread to start.

     tracer_thread_argument.mutex.Unlock();

     // NOTE: errno is shared between this thread and the tracer thread.