[DebugInfo] Fix /usr/lib/debug llvm-symbolizer lookup with relative paths

Summary:
rL189250 added a realpath call, and rL352916 because realpath breaks assumptions with some build systems. However, the /usr/lib/debug case has been clarified, falling back to /usr/lib/debug is currently broken if the obj passed in is a relative path. Adding a call to use absolute paths when falling back to /usr/lib/debug fixes that while still not making any realpath assumptions.

This also adds a --fallback-debug-path command line flag for testing (since we probably can't write to /usr/lib/debug from buildbot environments), but was also verified manually:

```
$ rm -f path/to/dwarfdump-test.elf-x86-64
$ strace llvm-symbolizer --obj=relative/path/to/dwarfdump-test.elf-x86-64.debuglink 0x40113f |& grep dwarfdump
```

Lookups went to relative/path/to/dwarfdump-test.elf-x86-64, relative/path/to/.debug/dwarfdump-test.elf-x86-64, and then finally /usr/lib/debug/absolute/path/to/dwarfdump-test.elf-x86-64.

Reviewers: dblaikie, samsonov

Reviewed By: dblaikie

Subscribers: krytarowski, aprantl, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57916

llvm-svn: 353730

llvm/include/llvm/DebugInfo/Symbolize/Symbolize.h

@@ -41,13 +41,16 @@ public:
     bool RelativeAddresses : 1;
     std::string DefaultArch;
     std::vector<std::string> DsymHints;
+    std::string FallbackDebugPath;
 
     Options(FunctionNameKind PrintFunctions = FunctionNameKind::LinkageName,
             bool UseSymbolTable = true, bool Demangle = true,
-            bool RelativeAddresses = false, std::string DefaultArch = "")
+            bool RelativeAddresses = false, std::string DefaultArch = "",
+            std::string FallbackDebugPath = "")
         : PrintFunctions(PrintFunctions), UseSymbolTable(UseSymbolTable),
           Demangle(Demangle), RelativeAddresses(RelativeAddresses),
-          DefaultArch(std::move(DefaultArch)) {}
+          DefaultArch(std::move(DefaultArch)),
+          FallbackDebugPath(std::move(FallbackDebugPath)) {}
   };
 
   LLVMSymbolizer(const Options &Opts = Options()) : Opts(Opts) {}

llvm/lib/DebugInfo/Symbolize/Symbolize.cpp

@@ -165,30 +165,40 @@ bool checkFileCRC(StringRef Path, uint32_t CRCHash) {
 
 bool findDebugBinary(const std::string &OrigPath,
                      const std::string &DebuglinkName, uint32_t CRCHash,
+                     const std::string &FallbackDebugPath,
                      std::string &Result) {
   SmallString<16> OrigDir(OrigPath);
   llvm::sys::path::remove_filename(OrigDir);
   SmallString<16> DebugPath = OrigDir;
-  // Try /path/to/original_binary/debuglink_name
+  // Try relative/path/to/original_binary/debuglink_name
   llvm::sys::path::append(DebugPath, DebuglinkName);
   if (checkFileCRC(DebugPath, CRCHash)) {
     Result = DebugPath.str();
     return true;
   }
-  // Try /path/to/original_binary/.debug/debuglink_name
+  // Try relative/path/to/original_binary/.debug/debuglink_name
   DebugPath = OrigDir;
   llvm::sys::path::append(DebugPath, ".debug", DebuglinkName);
   if (checkFileCRC(DebugPath, CRCHash)) {
     Result = DebugPath.str();
     return true;
   }
+  // Make the path absolute so that lookups will go to
+  // "/usr/lib/debug/full/path/to/debug", not
+  // "/usr/lib/debug/to/debug"
+  llvm::sys::fs::make_absolute(OrigDir);
+  if (!FallbackDebugPath.empty()) {
+    // Try <FallbackDebugPath>/absolute/path/to/original_binary/debuglink_name
+    DebugPath = FallbackDebugPath;
+  } else {
 #if defined(__NetBSD__)
-  // Try /usr/libdata/debug/path/to/original_binary/debuglink_name
-  DebugPath = "/usr/libdata/debug";
+    // Try /usr/libdata/debug/absolute/path/to/original_binary/debuglink_name
+    DebugPath = "/usr/libdata/debug";
 #else
-  // Try /usr/lib/debug/path/to/original_binary/debuglink_name
-  DebugPath = "/usr/lib/debug";
+    // Try /usr/lib/debug/absolute/path/to/original_binary/debuglink_name
+    DebugPath = "/usr/lib/debug";
 #endif
+  }
   llvm::sys::path::append(DebugPath, llvm::sys::path::relative_path(OrigDir),
                           DebuglinkName);
   if (checkFileCRC(DebugPath, CRCHash)) {
@@ -274,7 +284,8 @@ ObjectFile *LLVMSymbolizer::lookUpDebuglinkObject(const std::string &Path,
   std::string DebugBinaryPath;
   if (!getGNUDebuglinkContents(Obj, DebuglinkName, CRCHash))
     return nullptr;
-  if (!findDebugBinary(Path, DebuglinkName, CRCHash, DebugBinaryPath))
+  if (!findDebugBinary(Path, DebuglinkName, CRCHash, Opts.FallbackDebugPath,
+                       DebugBinaryPath))
     return nullptr;
   auto DbgObjOrErr = getOrCreateObject(DebugBinaryPath, ArchName);
   if (!DbgObjOrErr) {

llvm/test/DebugInfo/symbolize-gnu-debuglink-fallback.test

@@ -0,0 +1,22 @@
+# REQUIRES: shell
+# Ensures that .debuglink can fallback to a separate location. This is normally
+# /usr/lib/debug (or /usr/libdata/debug for NetBSD), but can be configured on
+# the command line (mainly for testing).
+
+RUN: rm -rf %t/foo %t/bar
+RUN: mkdir -p %t/foo %t/bar/%t/foo
+
+RUN: cp %p/Inputs/dwarfdump-test.elf-x86-64.debuglink %t/foo
+
+RUN: llvm-symbolizer --obj=%t/foo/dwarfdump-test.elf-x86-64.debuglink 0x40113f \
+RUN:   --fallback-debug-path=%t/bar | FileCheck %s --check-prefix=UNKNOWN
+
+UNKNOWN:      main
+UNKNOWN-NEXT: ??:0:0
+
+RUN: cp %p/Inputs/dwarfdump-test.elf-x86-64 %t/bar/%t/foo
+RUN: llvm-symbolizer --obj=%t/foo/dwarfdump-test.elf-x86-64.debuglink 0x40113f \
+RUN:   --fallback-debug-path=%t/bar | FileCheck %s --check-prefix=FOUND
+
+FOUND:      main
+FOUND-NEXT: /tmp/dbginfo{{[/\\]}}dwarfdump-test.cc:16

llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp

@@ -143,6 +143,10 @@ static cl::list<std::string> ClInputAddresses(cl::Positional,
                                               cl::desc("<input addresses>..."),
                                               cl::ZeroOrMore);
 
+static cl::opt<std::string>
+    ClFallbackDebugPath("fallback-debug-path", cl::init(""),
+                        cl::desc("Fallback path for debug binaries."));
+
 template<typename T>
 static bool error(Expected<T> &ResOrErr) {
   if (ResOrErr)
@@ -234,7 +238,8 @@ int main(int argc, char **argv) {
     ClDemangle = !ClNoDemangle;
 
   LLVMSymbolizer::Options Opts(ClPrintFunctions, ClUseSymbolTable, ClDemangle,
-                               ClUseRelativeAddress, ClDefaultArch);
+                               ClUseRelativeAddress, ClDefaultArch,
+                               ClFallbackDebugPath);
 
   for (const auto &hint : ClDsymHint) {
     if (sys::path::extension(hint) == ".dSYM") {