From f76c6b8d0a7966ab43d826dc3e19de4ccaa1f7e4 Mon Sep 17 00:00:00 2001
From: Jon Turney <jon.turney@dronecode.org.uk>
Date: Thu, 20 May 2021 23:12:38 +0100
Subject: Fix LTO test on Cygwin

This partially reverts commit add502c6483bde9dc6a0ba80b3c79163304465a4.

In 'linkshared' test, annotate cppfunc() as imported, so an indirection
through an import stub is generated, avoiding a relocation size error
when building using gcc for Cygwin with LTO on.

Align with the example of how to write this portably in [1].

The 'c' language part of that test already gets this right.

[1] http://gcc.gnu.org/wiki/Visibility
---
 run_unittests.py                           |  2 --
 test cases/common/6 linkshared/cpplib.cpp  |  7 ++-----
 test cases/common/6 linkshared/cpplib.h    | 12 ++++++++++++
 test cases/common/6 linkshared/cppmain.cpp |  2 +-
 4 files changed, 15 insertions(+), 8 deletions(-)
 create mode 100644 test cases/common/6 linkshared/cpplib.h

diff --git a/run_unittests.py b/run_unittests.py
index f65eba38d..ed8de784d 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -3075,8 +3075,6 @@ class AllPlatformTests(BasePlatformTests):
 
     @skip_if_not_base_option('b_lto_threads')
     def test_lto_threads(self):
-        if is_cygwin():
-            raise unittest.SkipTest('LTO is broken on Cygwin.')
         testdir = os.path.join(self.common_test_dir, '6 linkshared')
 
         env = get_fake_env(testdir, self.builddir, self.prefix)
diff --git a/test cases/common/6 linkshared/cpplib.cpp b/test cases/common/6 linkshared/cpplib.cpp
index 395859d27..247f8201a 100644
--- a/test cases/common/6 linkshared/cpplib.cpp	
+++ b/test cases/common/6 linkshared/cpplib.cpp	
@@ -1,8 +1,5 @@
-#if defined _WIN32
-    #define DLL_PUBLIC __declspec(dllexport)
-#else
-    #define DLL_PUBLIC __attribute__ ((visibility ("default")))
-#endif
+#define BUILDING_DLL
+#include "cpplib.h"
 
 int DLL_PUBLIC cppfunc(void) {
     return 42;
diff --git a/test cases/common/6 linkshared/cpplib.h b/test cases/common/6 linkshared/cpplib.h
new file mode 100644
index 000000000..e2b02060d
--- /dev/null
+++ b/test cases/common/6 linkshared/cpplib.h	
@@ -0,0 +1,12 @@
+/* See http://gcc.gnu.org/wiki/Visibility#How_to_use_the_new_C.2B-.2B-_visibility_support */
+#if defined(_WIN32) || defined(__CYGWIN__)
+  #ifdef BUILDING_DLL
+    #define DLL_PUBLIC __declspec(dllexport)
+  #else
+    #define DLL_PUBLIC __declspec(dllimport)
+  #endif
+#else
+    #define DLL_PUBLIC __attribute__ ((visibility ("default")))
+#endif
+
+int DLL_PUBLIC cppfunc(void);
diff --git a/test cases/common/6 linkshared/cppmain.cpp b/test cases/common/6 linkshared/cppmain.cpp
index 8e1648515..29e9a4480 100644
--- a/test cases/common/6 linkshared/cppmain.cpp	
+++ b/test cases/common/6 linkshared/cppmain.cpp	
@@ -1,4 +1,4 @@
-int cppfunc(void);
+#include "cpplib.h"
 
 int main(void) {
     return cppfunc() != 42;
-- 
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