[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

1 files changed, 18 insertions, 7 deletions

diff --git a/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp b/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
index 5f7370c9ae5..73fe9780f52 100644
--- a/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
+++ b/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) {