[libcxxabi] Fix exception address alignment test for EHABI

[rmaprath]

Summary

This test was failing on our downstream (bare-metal) runs and only now I got around to investigate it.

The problem is, this test assumes the Itanium ABI, whereas EHABI requires the exception address to be 8-byte aligned.

I was a bit puzzled at first because this should've failed on the public arm-linux builder too. I think the reason it passes there is because we don't include libunwind headers in the include path when running the libcxxabi tests, so the system unwind.h gets picked up.

[rmaprath]

Fixed a few paths.

[rengolin]

This looks like a simple oversight from my perspective, so looks good.

But I'll let the others have a look at it, as I'm not overly familiar with libcxxabi.

cheers,
--renato

[EricWF]

For the most part this LGTM other than the nits mentioned.

test/libcxxabi/test/config.py

34

I think the correct default here is None, not ../libunwind/src, since we might not be using libunwind at all.

93

I'm not sure if this is default is optimal. I think None might be less surprising.

test/lit.site.cfg.in

9

I don't think we need the unwind sources anywhere within the test suite. I would remove this option all together and simply depend on libunwind_headers.

10

I think libunwind_headers should be the empty string when LIBCXXABI_LIBUNWIND_INCLUDE_INTERNAL has not been found, instead of expanding to "LIBCXXABI_LIBUNWIND_INCLUDE_INTERNAL-NOTFOUND"

test/test_exception_address_alignment.pass.cpp

30

Shouldn't this be an #ifdef?

[rmaprath]

Addressed review comments from @EricWF .

CMakeLists.txt

     set(LIBCXXABI_LIBUNWIND_SOURCES "")
   endif()
 
-  if (NOT LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL STREQUAL "LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL-NOTFOUND")
+  if (LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL STREQUAL "LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL-NOTFOUND")
+    set(LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL "")
+  endif()
+
+  if (NOT LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL STREQUAL "")
     include_directories("${LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL}")
   endif()
+
   if (NOT LIBCXXABI_LIBUNWIND_SOURCES STREQUAL "")
     include_directories("${LIBCXXABI_LIBUNWIND_SOURCES}")
   endif()

test/libcxxabi/test/config.py

                                   % libcxxabi_headers)
         self.cxx.compile_flags += ['-I' + libcxxabi_headers]
 
+        libunwind_headers = self.get_lit_conf('libunwind_headers', None)
+        if self.get_lit_bool('llvm_unwinder', False) and libunwind_headers:
+            if not os.path.isdir(libunwind_headers):
+                self.lit_config.fatal("libunwind_headers='%s' is not a directory."
+                                      % libunwind_headers)
+            self.cxx.compile_flags += ['-I' + libunwind_headers]
+
     def configure_compile_flags_exceptions(self):
         pass
 

test/lit.site.cfg.in

 config.abi_library_path         = "@LIBCXXABI_LIBRARY_DIR@"
 config.libcxx_src_root          = "@LIBCXXABI_LIBCXX_PATH@"
 config.cxx_headers              = "@LIBCXXABI_LIBCXX_INCLUDES@"
+config.libunwind_headers        = "@LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL@"
 config.cxx_library_root         = "@LIBCXXABI_LIBCXX_LIBRARY_PATH@"
 config.llvm_unwinder            = "@LIBCXXABI_USE_LLVM_UNWINDER@"
 config.enable_threads           = "@LIBCXXABI_ENABLE_THREADS@"

test/test_exception_address_alignment.pass.cpp

 // working around this failure.
 // XFAIL: darwin && libcxxabi-has-system-unwinder
 
-// Test that the address of the exception object is properly aligned to the
-// largest supported alignment for the system.
+// Test that the address of the exception object is properly aligned as required
+// by the relevant ABI
 
 #include <cstdint>
 #include <cassert>

 #include <unwind.h>
 
 struct __attribute__((aligned)) AlignedType {};
-static_assert(alignof(AlignedType) == alignof(_Unwind_Exception),
+
+// EHABI  : 8-byte aligned
+// Itanium: Largest supported alignment for the system
+#if defined(_LIBUNWIND_ARM_EHABI)
+#  define EXPECTED_ALIGNMENT 8
+#else
+#  define EXPECTED_ALIGNMENT alignof(AlignedType)
+#endif
+
+static_assert(alignof(_Unwind_Exception) == EXPECTED_ALIGNMENT,
   "_Unwind_Exception is incorrectly aligned. This test is expected to fail");
 
 struct MinAligned {  };

     try {
       throw MinAligned{};
     } catch (MinAligned const& ref) {
-      assert(reinterpret_cast<uintptr_t>(&ref) % alignof(AlignedType) == 0);
+      assert(reinterpret_cast<uintptr_t>(&ref) % EXPECTED_ALIGNMENT == 0);
     }
   }
 }