Mark _r_debug imports as weak

Summary:
[Folly] Mark `_r_debug` imports as weak imports. `_r_debug` is available in `<link.h>` but is not a portable API, so detect whether it is available at runtime and use it only if it is available.

Fixes: https://github.com/facebook/folly/issues/1373.

Reviewed By: Orvid

Differential Revision: D21911715

fbshipit-source-id: 660c0bc90d405d9a43826e7bdfc3b04480728b66

folly/experimental/symbolizer/Symbolizer.cpp

@@ -47,7 +47,7 @@
  *
  * Note that declaring it with `extern "C"` results in linkage conflicts.
  */
-extern struct r_debug _r_debug;
+FOLLY_ATTR_WEAK extern struct r_debug _r_debug;
 
 namespace folly {
 namespace symbolizer {
@@ -83,6 +83,10 @@ void setSymbolizedFrame(
 
 } // namespace
 
+bool Symbolizer::isAvailable() {
+  return &_r_debug != nullptr;
+}
+
 Symbolizer::Symbolizer(
     ElfCacheBase* cache,
     LocationInfoMode mode,
@@ -101,6 +105,9 @@ size_t Symbolizer::symbolize(
   FOLLY_SAFE_CHECK(addrCount <= frameCount, "Not enough frames.");
   size_t remaining = addrCount;
 
+  if (&_r_debug == nullptr) {
+    return 0;
+  }
   if (_r_debug.r_version != 1) {
     return 0;
   }

folly/experimental/symbolizer/Symbolizer.h

@@ -89,6 +89,8 @@ class Symbolizer {
  public:
   static constexpr auto kDefaultLocationInfoMode = LocationInfoMode::FAST;
 
+  static bool isAvailable();
+
   explicit Symbolizer(LocationInfoMode mode = kDefaultLocationInfoMode)
       : Symbolizer(nullptr, mode) {}
 

folly/experimental/symbolizer/test/StackTraceTest.cpp

@@ -19,6 +19,7 @@
 #include <folly/experimental/TestUtil.h>
 #include <folly/experimental/symbolizer/StackTrace.h>
 #include <folly/experimental/symbolizer/Symbolizer.h>
+#include <folly/test/TestUtils.h>
 
 #include <boost/regex.hpp>
 
@@ -209,6 +210,8 @@ FOLLY_NOINLINE void baz(FrameArray<frames>& addresses) {
 } // namespace
 
 TEST(StackTraceTest, TerseFileAndLineStackTracePrinterOutput) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(LocationInfoMode::FULL);
   FrameArray<frames> addresses;
   StringSymbolizePrinter printer(SymbolizePrinter::TERSE_FILE_AND_LINE);

folly/experimental/symbolizer/test/SymbolizerTest.cpp

@@ -25,6 +25,7 @@
 #include <folly/experimental/symbolizer/SymbolizedFrame.h>
 #include <folly/experimental/symbolizer/test/SymbolizerTestUtils.h>
 #include <folly/portability/GTest.h>
+#include <folly/test/TestUtils.h>
 
 namespace folly {
 namespace symbolizer {
@@ -33,6 +34,8 @@ namespace test {
 void foo() {}
 
 TEST(Symbolizer, Single) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   // It looks like we could only use .debug_aranges with "-g2", with
   // "-g1 -gdwarf-aranges", the code has to fallback to line-tables to
   // get the file name.
@@ -70,6 +73,8 @@ class ElfCacheTest : public testing::Test {
 FrameArray<100> goldenFrames;
 
 void ElfCacheTest::SetUp() {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   bar(goldenFrames);
   Symbolizer symbolizer;
   symbolizer.symbolize(goldenFrames);
@@ -106,6 +111,8 @@ TEST_F(ElfCacheTest, SignalSafeElfCache) {
 }
 
 TEST(SymbolizerTest, SymbolCache) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL, 100);
 
   FrameArray<100> frames;
@@ -190,6 +197,8 @@ class ClassWithInlineFunctions {
 };
 
 TEST(SymbolizerTest, InlineFunctionBasic) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -229,6 +238,8 @@ TEST(SymbolizerTest, InlineFunctionBasic) {
 }
 
 TEST(SymbolizerTest, InlineFunctionWithoutEnoughFrames) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -261,6 +272,8 @@ TEST(SymbolizerTest, InlineFunctionWithoutEnoughFrames) {
 }
 
 TEST(SymbolizerTest, InlineFunctionInLexicalBlock) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -286,6 +299,8 @@ TEST(SymbolizerTest, InlineFunctionInLexicalBlock) {
 }
 
 TEST(SymbolizerTest, InlineFunctionInDifferentCompilationUnit) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -304,6 +319,8 @@ TEST(SymbolizerTest, InlineFunctionInDifferentCompilationUnit) {
 }
 
 TEST(SymbolizerTest, InlineClassMemberFunction) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -321,6 +338,8 @@ TEST(SymbolizerTest, InlineClassMemberFunction) {
 }
 
 TEST(SymbolizerTest, StaticInlineClassMemberFunction) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -337,6 +356,8 @@ TEST(SymbolizerTest, StaticInlineClassMemberFunction) {
 }
 
 TEST(SymbolizerTest, InlineClassMemberFunctionInDifferentFile) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -354,6 +375,8 @@ TEST(SymbolizerTest, InlineClassMemberFunctionInDifferentFile) {
 }
 
 TEST(SymbolizerTest, StaticInlineClassMemberFunctionInDifferentFile) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 0);
 
   FrameArray<100> frames;
@@ -371,6 +394,8 @@ TEST(SymbolizerTest, StaticInlineClassMemberFunctionInDifferentFile) {
 
 // No inline frames should be filled because of no extra frames.
 TEST(SymbolizerTest, InlineFunctionBasicNoExtraFrames) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 100);
   FrameArray<8> frames;
   inlineBar<8>(frames);
@@ -385,6 +410,8 @@ TEST(SymbolizerTest, InlineFunctionBasicNoExtraFrames) {
 }
 
 TEST(SymbolizerTest, InlineFunctionWithCache) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
   Symbolizer symbolizer(nullptr, LocationInfoMode::FULL_WITH_INLINE, 100);
 
   FrameArray<100> frames;