[PowerPC] Fix downcast from nullptr

[ngzhian]

Summary

getTargetStreamer() might return null (e.g. when running
inlined-strings.ll test), downcasting to a reference will be wrong. This
is detectable with -fsanitize=null.

[steven.zhang]

Missing test. And PPCAIXAsmPrinter::emitEndOfAsmFile also has issues if it could be null. And it seems that, we miss this check also in:

./AsmParser/PPCAsmParser.cpp:           getParser().getStreamer().getTargetStreamer());
./AsmParser/PPCAsmParser.cpp:           getParser().getStreamer().getTargetStreamer());
./AsmParser/PPCAsmParser.cpp:           getParser().getStreamer().getTargetStreamer());

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1416

null check ?

[ngzhian]

Add null check

[ngzhian]

I don't have a good idea how to add test for this. With an ASAN build with -fsanitize=null, we get an error when running inlined-strings.ll.

[steven.zhang]

It is better to have some tests. You can get it by adding assertion for TS and then, running the test to see if any test trigger this assertion. And please also fix this for PPCAIXAsmPrinter and PPCAsmParser together. Thank you.

[ngzhian]

Add some tests for null streamer. Fix more instances of downcast from nullptr.

[ngzhian]

Thanks for the advice, Steven. I found some existing tests that exercised the particular downcasting logic, and found that if I set -filetype=null in those RUN: directives, I could trigger a crash. So I added a line to those tests. Also made the same fix to PPCAsmParser and PPCAIXAsmPrinter.

[steven.zhang]

LGTM, thank you for the fixing.

[ngzhian]

Thanks Steven, I do not have commit access, can you please help me commit this?

[steven.zhang]

In D78686#2005604, @ngzhian wrote:

Thanks Steven, I do not have commit access, can you please help me commit this?

Sure.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

void PPCLinuxAsmPrinter::emitFunctionEntryLabel() {
   OutStreamer->SwitchSection(Current.first, Current.second);
 }
 
 void PPCLinuxAsmPrinter::emitEndOfAsmFile(Module &M) {
   const DataLayout &DL = getDataLayout();
 
   bool isPPC64 = DL.getPointerSizeInBits() == 64;
 
-  PPCTargetStreamer &TS =
-      static_cast<PPCTargetStreamer &>(*OutStreamer->getTargetStreamer());
+  PPCTargetStreamer *TS =
+      static_cast<PPCTargetStreamer *>(OutStreamer->getTargetStreamer());
 
   if (!TOC.empty()) {
     const char *Name = isPPC64 ? ".toc" : ".got2";
     MCSectionELF *Section = OutContext.getELFSection(
         Name, ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
     OutStreamer->SwitchSection(Section);
     if (!isPPC64)
       OutStreamer->emitValueToAlignment(4);
 
     for (const auto &TOCMapPair : TOC) {
       const MCSymbol *const TOCEntryTarget = TOCMapPair.first;
       MCSymbol *const TOCEntryLabel = TOCMapPair.second;
 
       OutStreamer->emitLabel(TOCEntryLabel);
       if (isPPC64)
-        TS.emitTCEntry(*TOCEntryTarget);
+        TS->emitTCEntry(*TOCEntryTarget);
       else
         OutStreamer->emitSymbolValue(TOCEntryTarget, 4);
     }
   }
 
   PPCAsmPrinter::emitEndOfAsmFile(M);
 }