Index: lldb/source/Host/macosx/objcxx/Host.mm
===================================================================
--- lldb/source/Host/macosx/objcxx/Host.mm
+++ lldb/source/Host/macosx/objcxx/Host.mm
@@ -38,6 +38,7 @@
 
 #include <asl.h>
 #include <crt_externs.h>
+#include <dlfcn.h>
 #include <grp.h>
 #include <libproc.h>
 #include <pwd.h>
@@ -1108,6 +1109,49 @@
     }
   }
 
+  // Don't set the binpref if a shell was provided. After all, that's only
+  // going to affect what version of the shell is launched, not what fork of
+  // the binary is launched.  We insert "arch --arch <ARCH> as part of the
+  // shell invocation to do that job on OSX.
+  if (launch_info.GetShell() == FileSpec()) {
+    const ArchSpec &arch_spec = launch_info.GetArchitecture();
+    cpu_type_t cpu_type = arch_spec.GetMachOCPUType();
+    cpu_type_t cpu_subtype = arch_spec.GetMachOCPUSubType();
+    if (cpu_type != 0 && cpu_type != static_cast<cpu_type_t>(UINT32_MAX) &&
+        cpu_type != static_cast<cpu_type_t>(LLDB_INVALID_CPUTYPE)) {
+      size_t ocount = 0;
+      typedef int (*posix_spawnattr_setarchpref_np_t)(
+          posix_spawnattr_t *, size_t, cpu_type_t *, cpu_subtype_t *, size_t *);
+      posix_spawnattr_setarchpref_np_t posix_spawnattr_setarchpref_np_fn =
+          (posix_spawnattr_setarchpref_np_t)dlsym(
+              RTLD_DEFAULT, "posix_spawnattr_setarchpref_np");
+      if (posix_spawnattr_setarchpref_np_fn) {
+        error.SetError((*posix_spawnattr_setarchpref_np_fn)(
+                           &attr, 1, &cpu_type, &cpu_subtype, &ocount),
+                       eErrorTypePOSIX);
+        if (error.Fail())
+          LLDB_LOG(log,
+                   "error: {0}, ::posix_spawnattr_setarchpref_np ( &attr, 1, "
+                   "cpu_type = {1:x}, cpu_subtype = {1:x}, count => {2} )",
+                   error, cpu_type, cpu_subtype, ocount);
+
+        if (error.Fail() || ocount != 1)
+          return error;
+      } else {
+        error.SetError(
+            ::posix_spawnattr_setbinpref_np(&attr, 1, &cpu_type, &ocount),
+            eErrorTypePOSIX);
+        if (error.Fail())
+          LLDB_LOG(log,
+                   "error: {0}, ::posix_spawnattr_setbinpref_np ( &attr, 1, "
+                   "cpu_type = {1:x}, count => {2} )",
+                   error, cpu_type, ocount);
+        if (error.Fail() || ocount != 1)
+          return error;
+      }
+    }
+  }
+
   const char *tmp_argv[2];
   char *const *argv = const_cast<char *const *>(
       launch_info.GetArguments().GetConstArgumentVector());