[lldb] Add ability to detect darwin host linker version to xfail tests

When Apple released its new linker, it had a subtle bug that caused
LLDB's TLS tests to fail. Unfortunately this means that TLS tests
are not going to work on machines that have affected versions of the
linker, so we should annotate the tests so that they only work when we
are confident the linker has the required fix.

I'm not completely satisfied with this implementation. That being said,
I believe that adding suport for linker versions in general is a
non-trivial change that would require far more thought. There are a few
challenges involved:
- LLDB's testing infra takes an argument to change the compiler, but
  there's no way to switch out the linker.
- There's no standard way to ask a compiler what linker it will use.
- There's no standard way to ask a linker what its version is. Many
  platforms have the same name for their linker (ld).
- Some platforms automatically switch out the linker underneath you. We
  do this for Windows tests (where we use LLD no matter what).

Given that this is affecting the tests on our CI, I think this is an
acceptable solution in the interim.

Author: bulbazord

lldb/packages/Python/lldbsuite/test/lldbplatformutil.py

@@ -3,6 +3,7 @@
 
 # System modules
 import itertools
+import json
 import re
 import subprocess
 import sys
@@ -16,6 +17,7 @@
 from . import lldbtest_config
 import lldbsuite.test.lldbplatform as lldbplatform
 from lldbsuite.test.builders import get_builder
+from lldbsuite.test.lldbutil import is_exe
 
 
 def check_first_register_readable(test_case):
@@ -333,3 +335,41 @@ def expectedCompiler(compilers):
             return True
 
     return False
+
+
+# This is a helper function to determine if a specific version of Xcode's linker
+# contains a TLS bug. We want to skip TLS tests if they contain this bug, but
+# adding a linker/linker_version conditions to a decorator is challenging due to
+# the number of ways linkers can enter the build process.
+def darwinLinkerHasTLSBug():
+    """Returns true iff a test is running on a darwin platform and the host linker is between versions 1000 and 1109."""
+    darwin_platforms = lldbplatform.translate(lldbplatform.darwin_all)
+    if getPlatform() not in darwin_platforms:
+        return False
+
+    linker_path = (
+        subprocess.check_output(["xcrun", "--find", "ld"]).rstrip().decode("utf-8")
+    )
+    if not is_exe(linker_path):
+        return False
+
+    raw_linker_info = (
+        subprocess.check_output([linker_path, "-version_details"])
+        .rstrip()
+        .decode("utf-8")
+    )
+    parsed_linker_info = json.loads(raw_linker_info)
+    if "version" not in parsed_linker_info:
+        return False
+
+    raw_version = parsed_linker_info["version"]
+    version = None
+    try:
+        version = int(raw_version)
+    except:
+        return False
+
+    if version is None:
+        return False
+
+    return 1000 <= version and version <= 1109

lldb/test/API/lang/c/tls_globals/TestTlsGlobals.py

@@ -40,6 +40,7 @@ def setUp(self):
     @skipIfWindows
     @skipIf(oslist=["linux"], archs=["arm", "aarch64"])
     @skipIf(oslist=no_match([lldbplatformutil.getDarwinOSTriples(), "linux"]))
+    @expectedFailureIf(lldbplatformutil.darwinLinkerHasTLSBug())
     def test(self):
         """Test thread-local storage."""
         self.build()