From b40f9038d2527cecbc07a4abdf792231b82db244 Mon Sep 17 00:00:00 2001
From: Andrew Morrow <acm@mongodb.com>
Date: Wed, 7 Apr 2021 17:23:16 -0400
Subject: SERVER-55737 Add an experiment for not requiring -rdynamic

---
 SConstruct                         | 46 ++++++++++++++++++++++++++++++--------
 src/mongo/util/SConscript          |  3 +++
 src/mongo/util/stacktrace_test.cpp | 16 ++++++++-----
 3 files changed, 50 insertions(+), 15 deletions(-)

diff --git a/SConstruct b/SConstruct
index 04eaa5bcff5..9e4cad24503 100644
--- a/SConstruct
+++ b/SConstruct
@@ -277,6 +277,7 @@ experimental_optimizations = [
     'builtin-memcmp',
     'fnsi',
     'nofp',
+    'nordyn',
     'sandybridge',
     'tbaa',
     'treevec',
@@ -2561,21 +2562,48 @@ if env.TargetOSIs('posix'):
 
     # SERVER-9761: Ensure early detection of missing symbols in dependent libraries at program
     # startup.
-    if env.TargetOSIs('darwin'):
-        if env.TargetOSIs('macOS'):
-            env.Append( LINKFLAGS=["-Wl,-bind_at_load"] )
-    else:
+    env.Append(
+        LINKFLAGS=[
+            "-Wl,-bind_at_load" if env.TargetOSIs('macOS') else "-Wl,-z,now",
+        ],
+    )
+
+    # We need to use rdynamic for backtraces with glibc unless we have libunwind.
+    nordyn = (env.TargetOSIs('darwin') or use_libunwind)
+
+    # And of course only do rdyn if the experimenter asked for it.
+    nordyn &= ("nordyn" in selected_experimental_optimizations)
+
+    if nordyn:
+        def export_symbol_generator(source, target, env, for_signature):
+            symbols = copy.copy(env.get('EXPORT_SYMBOLS', []))
+            for lib in libdeps.get_libdeps(source, target, env, for_signature):
+                if lib.env:
+                    symbols.extend(lib.env.get('EXPORT_SYMBOLS', []))
+            export_expansion = '${EXPORT_SYMBOL_FLAG}'
+            return [f'-Wl,{export_expansion}{symbol}' for symbol in symbols]
+        env['EXPORT_SYMBOL_GEN'] = export_symbol_generator
+
+        # For darwin, we need the leading underscore but for others we
+        # don't. Hacky but it works to jam that distinction into the
+        # flag itself, since it already differs on darwin.
+        if env.TargetOSIs('darwin'):
+            env['EXPORT_SYMBOL_FLAG'] = "-exported_symbol,_"
+        else:
+            env['EXPORT_SYMBOL_FLAG'] = "--export-dynamic-symbol,"
+
         env.Append(
-            LINKFLAGS=[
-                "-Wl,-z,now",
+            PROGLINKFLAGS=[
+                '$EXPORT_SYMBOL_GEN'
             ],
+        )
+    elif not env.TargetOSIs('darwin'):
+        env.Append(
             PROGLINKFLAGS=[
                 "-rdynamic",
-            ]
+            ],
         )
 
-    env.Append( LIBS=[] )
-
     #make scons colorgcc friendly
     for key in ('HOME', 'TERM'):
         try:
diff --git a/src/mongo/util/SConscript b/src/mongo/util/SConscript
index 681207594db..ee75e3724f5 100644
--- a/src/mongo/util/SConscript
+++ b/src/mongo/util/SConscript
@@ -761,6 +761,9 @@ stacktraceEnv.CppUnitTest(
         'stacktrace_test.cpp',
     ],
     LIBDEPS=stacktrace_test_LIBDEPS,
+    EXPORT_SYMBOLS=[
+        'mongo_stacktrace_test_detail_testFunctionWithLinkage',
+    ],
 )
 
 stacktraceEnv.Benchmark(
diff --git a/src/mongo/util/stacktrace_test.cpp b/src/mongo/util/stacktrace_test.cpp
index feac7aa72aa..2a9ad180c28 100644
--- a/src/mongo/util/stacktrace_test.cpp
+++ b/src/mongo/util/stacktrace_test.cpp
@@ -69,13 +69,17 @@
 #include <unistd.h>
 #endif  //  __linux__
 
+// Needs to have linkage so we can test metadata. Needs to be extern
+// "C" so it doesn't get mangled so we can name it with EXPORT_SYMBOLS
+// in SConscript.
+extern "C" MONGO_COMPILER_NOINLINE MONGO_COMPILER_API_EXPORT void
+mongo_stacktrace_test_detail_testFunctionWithLinkage() {
+    printf("...");
+}
+
 namespace mongo {
 
 namespace stack_trace_test_detail {
-/** Needs to have linkage so we can test metadata. */
-MONGO_COMPILER_NOINLINE MONGO_COMPILER_API_EXPORT void testFunctionWithLinkage() {
-    printf("...");
-}
 
 struct RecursionParam {
     std::uint64_t n;
@@ -320,7 +324,7 @@ TEST(StackTrace, MetadataGenerator) {
         std::string symbolSub;
     } const tests[] = {
         {
-            reinterpret_cast<void*>(&stack_trace_test_detail::testFunctionWithLinkage),
+            reinterpret_cast<void*>(&mongo_stacktrace_test_detail_testFunctionWithLinkage),
             "stacktrace_test",
             "testFunctionWithLinkage",
         },
@@ -356,7 +360,7 @@ TEST(StackTrace, MetadataGeneratorFunctionMeasure) {
     // Measure the size of a C++ function as a test of metadata retrieval.
     // Load increasing addresses until the metadata's symbol name changes.
     StackTraceAddressMetadataGenerator gen;
-    void* fp = reinterpret_cast<void*>(&stack_trace_test_detail::testFunctionWithLinkage);
+    void* fp = reinterpret_cast<void*>(&mongo_stacktrace_test_detail_testFunctionWithLinkage);
     const auto& meta = gen.load(fp);
     if (!meta.symbol())
         return;  // No symbol for `fp`. forget it.
-- 
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