diff --git a/tools/clang/test/taef_exec/lit.cfg b/tools/clang/test/taef_exec/lit.cfg
index af52cd8867..f3c2d4dce2 100644
--- a/tools/clang/test/taef_exec/lit.cfg
+++ b/tools/clang/test/taef_exec/lit.cfg
@@ -47,12 +47,9 @@ Execution tests require DXIL.dll to sign shaders, or the experimental shader mod
 if config.unsupported == False:
   test_dll = os.path.join(bin_dir, 'ExecHLSLTests.dll')
 
-  hlsl_data_dir = os.path.join(config.llvm_src_root, 'tools', 'clang', 'unittests', 'HLSLExec')
-
   test_dir = os.path.join(config.llvm_obj_root, config.llvm_build_mode, 'test')
-  param_hlsl_data_dir = str.format('HlslDataDir={}', hlsl_data_dir)
 
-  extra_params = ['/p:', 'ExperimentalShaders=*', '/p:', param_hlsl_data_dir]
+  extra_params = ['/p:', 'ExperimentalShaders=*']
 
   verbose = bool(getattr(config, 'verbose', False))
   if verbose != True:
diff --git a/tools/clang/unittests/HLSLExec/HlslExecTestUtils.cpp b/tools/clang/unittests/HLSLExec/HlslExecTestUtils.cpp
index 91b813ed1e..3d787dc5f9 100644
--- a/tools/clang/unittests/HLSLExec/HlslExecTestUtils.cpp
+++ b/tools/clang/unittests/HLSLExec/HlslExecTestUtils.cpp
@@ -11,6 +11,7 @@
 #include <d3d12.h>
 #include <dxgi1_4.h>
 #include <filesystem>
+#include <mutex>
 #include <optional>
 
 // D3D12_FEATURE_D3D12_OPTIONS_PREVIEW and its data struct are not yet in
@@ -425,6 +426,118 @@ static bool createDevice(
   return true;
 }
 
+// Linker-provided symbol at the base of the module containing this code, which
+// is also its HMODULE. Identifies the module without depending on the name of
+// the binary these sources are built into.
+// See https://devblogs.microsoft.com/oldnewthing/20041025-00/?p=37483.
+extern "C" IMAGE_DOS_HEADER __ImageBase;
+
+// Directory of the module containing this code.
+static const std::wstring &getContainingModuleDirectory() {
+  static const std::wstring Dir = [] {
+    HMODULE Module = reinterpret_cast<HMODULE>(&__ImageBase);
+
+    // GetModuleFileNameW truncates rather than failing, so grow until it fits.
+    std::wstring Path(MAX_PATH, L'\0');
+    for (;;) {
+      const DWORD Len =
+          GetModuleFileNameW(Module, &Path[0], static_cast<DWORD>(Path.size()));
+      if (Len == 0)
+        return std::wstring();
+      if (Len < Path.size()) {
+        Path.resize(Len);
+        break;
+      }
+      Path.resize(Path.size() * 2);
+    }
+    return std::filesystem::path(Path).parent_path().wstring();
+  }();
+  return Dir;
+}
+
+// Every call site loads from the same directory, so log the first resolution
+// only. Tests may run in parallel, so this has to be thread-safe.
+static void logResolvedDataDirOnce(const wchar_t *Origin,
+                                   const std::filesystem::path &Path) {
+  static std::once_flag Logged;
+  std::call_once(Logged, [&] {
+    LogCommentFmt(L"Loading execution test data from %s: %s", Origin,
+                  Path.parent_path().c_str());
+  });
+}
+
+// Resolves a data file shipped with the execution tests, in this order:
+//
+//   1. the HlslDataDir runtime parameter, if supplied. Authoritative: we fail
+//      rather than fall through, so a typo is reported instead of hidden.
+//   2. the directory containing this module, so a binary deployed with its
+//      data files finds them.
+//   3. the source directory recorded by CMake, so a build tree picks up edits
+//      to the data files without rebuilding.
+static std::wstring resolveHlslDataFile(LPCWSTR RelativePath) {
+  WEX::Common::String ParamValue;
+  std::wstring OverrideDir;
+  if (SUCCEEDED(WEX::TestExecution::RuntimeParameters::TryGetValue(
+          HLSLDATAFILEPARAM, ParamValue)))
+    OverrideDir = reinterpret_cast<const wchar_t *>(ParamValue.GetBuffer());
+
+  // Treat an empty value as absent and fall through to the other locations.
+  if (!OverrideDir.empty()) {
+    std::filesystem::path Candidate =
+        std::filesystem::path(OverrideDir) / RelativePath;
+    if (!std::filesystem::exists(Candidate))
+      LOG_ERROR_FMT_THROW(
+          L"Unable to find %s in the directory given by the %s parameter.\n"
+          L"  Tried: %s\n"
+          L"%s is authoritative, so no other location was searched. Omit it "
+          L"to search the test binary's directory and the source directory.",
+          RelativePath, HLSLDATAFILEPARAM, Candidate.c_str(),
+          HLSLDATAFILEPARAM);
+    logResolvedDataDirOnce(
+        FormatToWString(L"the %s parameter", HLSLDATAFILEPARAM).c_str(),
+        Candidate);
+    return Candidate.wstring();
+  }
+
+  const std::wstring ModuleDir = getContainingModuleDirectory();
+  std::filesystem::path ModuleCandidate;
+  if (!ModuleDir.empty()) {
+    ModuleCandidate = std::filesystem::path(ModuleDir) / RelativePath;
+    if (std::filesystem::exists(ModuleCandidate)) {
+      logResolvedDataDirOnce(L"the directory containing the test binary",
+                             ModuleCandidate);
+      return ModuleCandidate.wstring();
+    }
+  }
+
+  // Empty in _HLK_CONF builds; probing it would just look in the current
+  // directory.
+  const std::wstring SourceDir = DEFAULT_EXEC_TEST_DIR;
+  std::filesystem::path SourceCandidate;
+  if (!SourceDir.empty()) {
+    SourceCandidate = std::filesystem::path(SourceDir) / RelativePath;
+    if (std::filesystem::exists(SourceCandidate)) {
+      logResolvedDataDirOnce(L"the build-configured source directory",
+                             SourceCandidate);
+      return SourceCandidate.wstring();
+    }
+  }
+
+  LOG_ERROR_FMT_THROW(
+      L"Unable to find the test data file %s in any known location.\n"
+      L"  Next to the test binary:      %s\n"
+      L"  Build-configured source path: %s\n"
+      L"Deploy %s next to the test binary, or pass "
+      L"/p:\"%s=<directory containing %s>\" to specify its location.",
+      RelativePath,
+      ModuleCandidate.empty() ? L"<could not determine the binary's directory>"
+                              : ModuleCandidate.c_str(),
+      SourceCandidate.empty() ? L"<not configured for this build>"
+                              : SourceCandidate.c_str(),
+      RelativePath, HLSLDATAFILEPARAM, RelativePath);
+  return std::wstring();
+}
+
 void readHlslDataIntoNewStream(LPCWSTR RelativePath, IStream **Stream,
                                dxc::SpecificDllLoader &Support) {
   VERIFY_SUCCEEDED(
@@ -432,8 +545,7 @@ void readHlslDataIntoNewStream(LPCWSTR RelativePath, IStream **Stream,
   CComPtr<IDxcLibrary> Library;
   CComPtr<IDxcBlobEncoding> Blob;
   CComPtr<IStream> StreamCom;
-  std::wstring Path = GetPathToHlslDataFile(RelativePath, HLSLDATAFILEPARAM,
-                                            DEFAULT_EXEC_TEST_DIR);
+  std::wstring Path = resolveHlslDataFile(RelativePath);
   VERIFY_SUCCEEDED(Support.CreateInstance(CLSID_DxcLibrary, &Library));
   VERIFY_SUCCEEDED(Library->CreateBlobFromFile(Path.c_str(), nullptr, &Blob));
   VERIFY_SUCCEEDED(Library->CreateStreamFromBlobReadOnly(Blob, &StreamCom));
diff --git a/utils/hct/hcttest.cmd b/utils/hct/hcttest.cmd
index 3e81d207e5..eebc531c91 100644
--- a/utils/hct/hcttest.cmd
+++ b/utils/hct/hcttest.cmd
@@ -454,7 +454,7 @@ if "%TEST_EXEC%"=="1" (
   call :copyagility
 )
 
-set EXEC_COMMON_ARGS=/p:"HlslDataDir=%HLSL_SRC_DIR%\tools\clang\unittests\HLSLExec" /p:"ExperimentalShaders=*" %TEST_ADAPTER% %USE_AGILITY_SDK%
+set EXEC_COMMON_ARGS=/p:"ExperimentalShaders=*" %TEST_ADAPTER% %USE_AGILITY_SDK%
 if "%TEST_EXEC%"=="1" (
   echo Sniffing for D3D12 configuration ...
   call :runte ExecHLSLTests.dll /select:"@Name='ExecutionTest::BasicTriangleTest' AND @Architecture='%TEST_ARCH%'" %EXEC_COMMON_ARGS%