[llvm-dev] [lld] ObjFile::createRegular is oblivious of PendingComdat

[Pirama Arumuga Nainar via llvm-dev]

I encountered a segfault when using lld to cross-compile for Windows
(+MinGW) from Linux.  The problem happens with objects built by gcc.  The
problem is that ObjFile::CreateRegular considers a PendingComdat to be
valid (and later causes an illegal pointer dereference).  The following
patch fixes the crash:

diff --git a/COFF/InputFiles.cpp b/COFF/InputFiles.cpp
index 9e2345b0a..f47d612df 100644
--- a/COFF/InputFiles.cpp
+++ b/COFF/InputFiles.cpp
@@ -229,11 +229,11 @@ Symbol *ObjFile::createRegular(COFFSymbolRef Sym) {
   if (Sym.isExternal()) {
     StringRef Name;
     COFFObj->getSymbolName(Sym, Name);
-    if (SC)
+    if (SC && SC != PendingComdat)
       return Symtab->addRegular(this, Name, Sym.getGeneric(), SC);
     return Symtab->addUndefined(Name, this, false);
   }
-  if (SC)
+  if (SC && SC != PendingComdat)
     return make<DefinedRegular>(this, /*Name*/ "", false,
                                 /*IsExternal*/ false, Sym.getGeneric(),
SC);
   return nullptr;

I can upload this to Phabricator in case this is the right fix.  If not,
I'll upload a reproducer for further investigation.  (I omitted it to avoid
manually packaging a whole set of object files - I think
--reproduce=<repro> doesn't work on Windows yet).

For reference, here's the segfault:
#0 0x0000000000500999 llvm::sys::PrintStackTrace(llvm::raw_ostream&)
/ssd2/pirama/ll$
m-upstream/llvm/lib/Support/Unix/Signals.inc:488:11
#1 0x0000000000500b49 PrintStackTraceSignalHandler(void*)
/ssd2/pirama/llvm-upstream$
llvm/lib/Support/Unix/Signals.inc:552:1
#2 0x00000000004ff1d6 llvm::sys::RunSignalHandlers()
/ssd2/pirama/llvm-upstream/llvm$
lib/Support/Signals.cpp:66:5
#3 0x0000000000500eb7 SignalHandler(int)
/ssd2/pirama/llvm-upstream/llvm/lib/Support$
Unix/Signals.inc:351:1
#4 0x00007fc7bfaff0c0 __restore_rt
(/lib/x86_64-linux-gnu/libpthread.so.0+0x110c0)
#5 0x00000000005fe370 lld::coff::DefinedRegular::getChunk() const
/ssd2/pirama/llvm-$
pstream/llvm/tools/lld/COFF/Symbols.h:169:43

#6 0x00000000005fe082 lld::coff::Defined::getChunk()
/ssd2/pirama/llvm-upstream/llvm$
tools/lld/COFF/Symbols.h:381:5

#7 0x0000000000656114 (anonymous
namespace)::Writer::createSymbol(lld::coff::Defined$
) /ssd2/pirama/llvm-upstream/llvm/tools/lld/COFF/Writer.cpp:617:42

#8 0x000000000064c7df (anonymous
namespace)::Writer::createSymbolAndStringTable() /s$
d2/pirama/llvm-upstream/llvm/tools/lld/COFF/Writer.cpp:0:43

#9 0x00000000006499f9 (anonymous namespace)::Writer::run()
/ssd2/pirama/llvm-upstrea$
/llvm/tools/lld/COFF/Writer.cpp:342:3

#10 0x0000000000649843 lld::coff::writeResult()
/ssd2/pirama/llvm-upstream/llvm/tool$
/lld/COFF/Writer.cpp:232:31

#11 0x00000000005d1268 lld::coff::LinkerDriver::link(llvm::ArrayRef<char
const*>) /s$
d2/pirama/llvm-upstream/llvm/tools/lld/COFF/Driver.cpp:1536:3
#12 0x00000000005c8687 lld::coff::link(llvm::ArrayRef<char const*>, bool,
llvm::raw_$
stream&) /ssd2/pirama/llvm-upstream/llvm/tools/lld/COFF/Driver.cpp:75:7
#13 0x0000000000946db0 lld::mingw::link(llvm::ArrayRef<char const*>,
llvm::raw_ostrea
m&) /ssd2/pirama/llvm-upstream/llvm/tools/lld/MinGW/Driver.cpp:255:10
#14 0x00000000004d02a8 main
/ssd2/pirama/llvm-upstream/llvm/tools/lld/tools/lld/lld.c
pp:121:14
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