[DebugInfo] Don't use realpath when looking up debug binary locations.

[rupprecht]

Summary

Using realpath makes assumptions about build systems that do not always hold true. The debug binary referred to from the .gnu_debuglink should exist in the same directory (or in a .debug directory, etc.), but the files may only exist as symlinks to a differently named files elsewhere, and using realpath causes that lookup to fail.

This was added in r189250, and this is basically a revert + regression test case.

[dblaikie]

In the absence of further info about the original commit/intended functionality - sure. If it breaks, we'll at least know why it was this way in the first place. :)

llvm/test/DebugInfo/symbolize-gnu-debuglink-no-realpath.test

6–7

Perhaps name the directories "real" and "sym" so they're more self explanatory?

[rupprecht]

• Use real/syms instead of objs/runfiles

[samsonov]

Ugh, too bad the original commit didn't provide any rationale, but here's my guess based on reading the source code:

Note that llvm-symbolizer (or another tool that uses this library) can be invoked with the relative path (e.g. cd /tmp/dir; llvm-symbolizer foo).

Then, if you can't find the .debuglink file at following locations: foo.debuglink (absolute path /tmp/dir/foo.debuglink), or .debug/foo.debuglink (absolute path /tmp/dir/.debuglink/foo.debuglink),
which can often happen if you're symbolizing the code from standard library, you have to look for this file in /usr/lib/... or /usr/libdata/... for NetBSD. That's when you need the realpath for the file in question,
so that you try to open:

/usr/lib/debug/tmp/dir/foo.debuglink

instead of

/usr/lib/debug/foo.debuglink

[rupprecht]

In D57609#1387458, @samsonov wrote:

Ugh, too bad the original commit didn't provide any rationale, but here's my guess based on reading the source code:

Note that llvm-symbolizer (or another tool that uses this library) can be invoked with the relative path (e.g. cd /tmp/dir; llvm-symbolizer foo).

Then, if you can't find the .debuglink file at following locations: foo.debuglink (absolute path /tmp/dir/foo.debuglink), or .debug/foo.debuglink (absolute path /tmp/dir/.debuglink/foo.debuglink),
which can often happen if you're symbolizing the code from standard library, you have to look for this file in /usr/lib/... or /usr/libdata/... for NetBSD. That's when you need the realpath for the file in question,
so that you try to open:

/usr/lib/debug/tmp/dir/foo.debuglink

instead of

/usr/lib/debug/foo.debuglink

I think the absolute path (not realpath) would suffice, then.

Also, using the full path can be delayed to when checking in /usr/lib/debug.

I'll restore this patch with those modifications. No idea how I'll create a test for it though -- writing to /usr/lib/debug probably doesn't work on buildbots.

[rupprecht]

In D57609#1389282, @rupprecht wrote:

In D57609#1387458, @samsonov wrote:

Ugh, too bad the original commit didn't provide any rationale, but here's my guess based on reading the source code:

Note that llvm-symbolizer (or another tool that uses this library) can be invoked with the relative path (e.g. cd /tmp/dir; llvm-symbolizer foo).

Then, if you can't find the .debuglink file at following locations: foo.debuglink (absolute path /tmp/dir/foo.debuglink), or .debug/foo.debuglink (absolute path /tmp/dir/.debuglink/foo.debuglink),
which can often happen if you're symbolizing the code from standard library, you have to look for this file in /usr/lib/... or /usr/libdata/... for NetBSD. That's when you need the realpath for the file in question,
so that you try to open:

/usr/lib/debug/tmp/dir/foo.debuglink

instead of

/usr/lib/debug/foo.debuglink

I think the absolute path (not realpath) would suffice, then.

Also, using the full path can be delayed to when checking in /usr/lib/debug.

I'll restore this patch with those modifications. No idea how I'll create a test for it though -- writing to /usr/lib/debug probably doesn't work on buildbots.

Mailed D57916

llvm/lib/DebugInfo/Symbolize/Symbolize.cpp

 //===----------------------------------------------------------------------===//
 
 #include "llvm/DebugInfo/Symbolize/Symbolize.h"
 
 #include "SymbolizableObjectFile.h"
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/BinaryFormat/COFF.h"
-#include "llvm/Config/config.h"
 #include "llvm/DebugInfo/DWARF/DWARFContext.h"
 #include "llvm/DebugInfo/PDB/PDB.h"
 #include "llvm/DebugInfo/PDB/PDBContext.h"
 #include "llvm/Demangle/Demangle.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Object/MachO.h"
 #include "llvm/Object/MachOUniversal.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include <algorithm>
 #include <cassert>
-#include <cstdlib>
 #include <cstring>
 
 #if defined(_MSC_VER)
 #include <Windows.h>
 
 // This must be included after windows.h.
 #include <DbgHelp.h>
 #pragma comment(lib, "dbghelp.lib")
bool checkFileCRC(StringRef Path, uint32_t CRCHash) {
   if (!MB)
     return false;
   return !zlib::isAvailable() || CRCHash == zlib::crc32(MB.get()->getBuffer());
 }
 
 bool findDebugBinary(const std::string &OrigPath,
                      const std::string &DebuglinkName, uint32_t CRCHash,
                      std::string &Result) {
-  std::string OrigRealPath = OrigPath;
-#if defined(HAVE_REALPATH)
-  if (char *RP = realpath(OrigPath.c_str(), nullptr)) {
-    OrigRealPath = RP;
-    free(RP);
-  }
-#endif
-  SmallString<16> OrigDir(OrigRealPath);
+  SmallString<16> OrigDir(OrigPath);
   llvm::sys::path::remove_filename(OrigDir);
   SmallString<16> DebugPath = OrigDir;
   // Try /path/to/original_binary/debuglink_name
   llvm::sys::path::append(DebugPath, DebuglinkName);
   if (checkFileCRC(DebugPath, CRCHash)) {
     Result = DebugPath.str();
     return true;
   }

llvm/test/DebugInfo/symbolize-gnu-debuglink-no-realpath.test

+# REQUIRES: shell
+# Ensure that no realpath assumptions are made about .gnu_debuglink paths.
+
+# Copy inputs to some other location with arbitrary names, with the original
+# filenames just being symlinks to the copies. Real files go in the "real" dir,
+# symlinks (with original names) go in "syms".
+RUN: rm -rf %t/real %t/syms
+RUN: mkdir %t/real %t/syms
+RUN: cp %p/Inputs/dwarfdump-test.elf-x86-64 %t/real/prog
+RUN: cp %p/Inputs/dwarfdump-test.elf-x86-64.debuglink %t/real/link
+RUN: ln -s %t/real/prog %t/syms/dwarfdump-test.elf-x86-64
+RUN: ln -s %t/real/link %t/syms/dwarfdump-test.elf-x86-64.debuglink
+
+RUN: llvm-symbolizer --obj=%t/syms/dwarfdump-test.elf-x86-64.debuglink 0x40113f | FileCheck %s
+
+CHECK:       main
+CHECK-NEXT: /tmp/dbginfo{{[/\\]}}dwarfdump-test.cc:16