[COFF] Handle comdat sections without leader symbols

Discard them unless they have been associated by other means (yet
uimplemented).

According to MS link.exe, such sections are illegal, but MinGW setups
use them in their take on associative comdats.

This avoids leaving references to the bogus SectionChunk* PendingComdat,
which cannot be dereferenced.

This fixes PR38183.

Differential Revision: https://reviews.llvm.org/D49653

llvm-svn: 338064

2 files changed, 28 insertions, 0 deletions

diff --git a/lld/COFF/InputFiles.cpp b/lld/COFF/InputFiles.cpp
index 2788f3b2f71..2b3e65fae04 100644
--- a/lld/COFF/InputFiles.cpp
+++ b/lld/COFF/InputFiles.cpp
@@ -281,6 +281,13 @@ void ObjFile::initializeSymbols() {
     if (auto *Def = Sym.getSectionDefinition())
       if (Def->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
         readAssociativeDefinition(Sym, Def);
+    if (SparseChunks[Sym.getSectionNumber()] == PendingComdat) {
+      StringRef Name;
+      COFFObj->getSymbolName(Sym, Name);
+      log("comdat section " + Name +
+          " without leader and unassociated, discarding");
+      continue;
+    }
     Symbols[I] = createRegular(Sym);
   }
 
diff --git a/lld/test/COFF/pending-comdat.s b/lld/test/COFF/pending-comdat.s
new file mode 100644
index 00000000000..b10dce1f1ea
--- /dev/null
+++ b/lld/test/COFF/pending-comdat.s
@@ -0,0 +1,21 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -triple=x86_64-windows-gnu %s -filetype=obj -o %t.obj
+
+# RUN: not lld-link -lldmingw -out:%t.exe -entry:main -subsystem:console %t.obj 2>&1 | FileCheck %s
+
+# CHECK: error: undefined symbol: other
+
+# Check that the comdat section without a symbol isn't left pending once we iterate symbols
+# to print source of the undefined symbol.
+
+	.text
+	.globl main
+main:
+	call other
+	ret
+
+	.section	.data$pending,"w"
+	.linkonce	discard
+.Llocal:
+	.byte	0