[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, 6 insertions, 1 deletions

diff --git a/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp b/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
index 0b0b8a68a4a..8ff7a22a71a 100644
--- a/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
+++ b/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") {