1 files changed, 49 insertions, 10 deletions

diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index 37e4c8a..a5921fe 100644
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -20,6 +20,7 @@
 #include "llvm/ADT/CachedHashString.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/LTO/LTO.h"
+#include "llvm/Object/Archive.h"
 #include "llvm/Object/IRObjectFile.h"
 #include "llvm/Support/AArch64AttributeParser.h"
 #include "llvm/Support/ARMAttributeParser.h"
@@ -1811,6 +1812,39 @@ static uint8_t getOsAbi(const Triple &t) {
   }
 }
 
+// For DTLTO, bitcode member names must be valid paths to files on disk.
+// For thin archives, resolve `memberPath` relative to the archive's location.
+// Returns true if adjusted; false otherwise. Non-thin archives are unsupported.
+static bool dtltoAdjustMemberPathIfThinArchive(Ctx &ctx, StringRef archivePath,
+                                               std::string &memberPath) {
+  assert(!archivePath.empty());
+
+  if (ctx.arg.dtltoDistributor.empty())
+    return false;
+
+  // Read the archive header to determine if it's a thin archive.
+  auto bufferOrErr =
+      MemoryBuffer::getFileSlice(archivePath, sizeof(ThinArchiveMagic) - 1, 0);
+  if (std::error_code ec = bufferOrErr.getError()) {
+    ErrAlways(ctx) << "cannot open " << archivePath << ": " << ec.message();
+    return false;
+  }
+
+  if (!bufferOrErr->get()->getBuffer().starts_with(ThinArchiveMagic))
+    return false;
+
+  SmallString<128> resolvedPath;
+  if (path::is_relative(memberPath)) {
+    resolvedPath = path::parent_path(archivePath);
+    path::append(resolvedPath, memberPath);
+  } else
+    resolvedPath = memberPath;
+
+  path::remove_dots(resolvedPath, /*remove_dot_dot=*/true);
+  memberPath = resolvedPath.str();
+  return true;
+}
+
 BitcodeFile::BitcodeFile(Ctx &ctx, MemoryBufferRef mb, StringRef archiveName,
                          uint64_t offsetInArchive, bool lazy)
     : InputFile(ctx, BitcodeKind, mb) {
@@ -1821,17 +1855,22 @@ BitcodeFile::BitcodeFile(Ctx &ctx, MemoryBufferRef mb, StringRef archiveName,
   if (ctx.arg.thinLTOIndexOnly)
     path = replaceThinLTOSuffix(ctx, mb.getBufferIdentifier());
 
-  // ThinLTO assumes that all MemoryBufferRefs given to it have a unique
-  // name. If two archives define two members with the same name, this
-  // causes a collision which result in only one of the objects being taken
-  // into consideration at LTO time (which very likely causes undefined
-  // symbols later in the link stage). So we append file offset to make
-  // filename unique.
   StringSaver &ss = ctx.saver;
-  StringRef name = archiveName.empty()
-                       ? ss.save(path)
-                       : ss.save(archiveName + "(" + path::filename(path) +
-                                 " at " + utostr(offsetInArchive) + ")");
+  StringRef name;
+  if (archiveName.empty() ||
+      dtltoAdjustMemberPathIfThinArchive(ctx, archiveName, path)) {
+    name = ss.save(path);
+  } else {
+    // ThinLTO assumes that all MemoryBufferRefs given to it have a unique
+    // name. If two archives define two members with the same name, this
+    // causes a collision which result in only one of the objects being taken
+    // into consideration at LTO time (which very likely causes undefined
+    // symbols later in the link stage). So we append file offset to make
+    // filename unique.
+    name = ss.save(archiveName + "(" + path::filename(path) + " at " +
+                   utostr(offsetInArchive) + ")");
+  }
+
   MemoryBufferRef mbref(mb.getBuffer(), name);
 
   obj = CHECK2(lto::InputFile::create(mbref), this);