[llvm] r316679 - Clear LastMappingSymbols and LastEMS(Info) when resetting the ARM(AArch64)ELFStreamer

[Yichao Yu via llvm-commits]

Author: yuyichao
Date: Thu Oct 26 10:36:43 2017
New Revision: 316679

URL: http://llvm.org/viewvc/llvm-project?rev=316679&view=rev
Log:
Clear LastMappingSymbols and LastEMS(Info) when resetting the ARM(AArch64)ELFStreamer

Summary:
This causes a segfault on ARM when (I think) the pass manager is used multiple times.

Reset set the (last) current section to NULL without saving the corresponding LastEMSInfo back into the map. The next use of the streamer then save the LastEMSInfo for the NULL section leaving the LastEMSInfo mapping for the last current section (the one that was there before the reset) NULL which cause the LastEMSInfo to be set to NULL when the section is being used again.

The reuse of the section (pointer) might mean that the map was holding dangling pointers previously which is why I went for clearing the map and resetting the info, making it as similar to the state right after the constructor run as possible. The AArch64 one doesn't have segfault (since LastEMS isn't a pointer) but it seems to have the same issue.

The segfault is likely caused by https://reviews.llvm.org/D30724 which turns LastEMSInfo into a pointer. As mentioned above, it seems that the actual issue was older though.

No test is included since the test is believed to be too complicated for such an obvious fix and not worth doing.

Reviewers: llvm-commits, shankare, t.p.northover, peter.smith, rengolin

Reviewed By: rengolin

Subscribers: mgorny, aemerson, rengolin, javed.absar, kristof.beyls

Differential Revision: https://reviews.llvm.org/D38588

Modified:
    llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
    llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp

Modified: llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp?rev=316679&r1=316678&r2=316679&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp (original)
+++ llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp Thu Oct 26 10:36:43 2017
@@ -102,6 +102,14 @@ public:
     MCELFStreamer::ChangeSection(Section, Subsection);
   }
 
+  // Reset state between object emissions
+  void reset() override {
+    MappingSymbolCounter = 0;
+    MCELFStreamer::reset();
+    LastMappingSymbols.clear();
+    LastEMS = EMS_None;
+  }
+
   /// This function is the one used to emit instruction data into the ELF
   /// streamer. We override it to add the appropriate mapping symbol if
   /// necessary.

Modified: llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp?rev=316679&r1=316678&r2=316679&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp (original)
+++ llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp Thu Oct 26 10:36:43 2017
@@ -1171,6 +1171,8 @@ void ARMELFStreamer::reset() {
   ATS.reset();
   MappingSymbolCounter = 0;
   MCELFStreamer::reset();
+  LastMappingSymbols.clear();
+  LastEMSInfo.reset();
   // MCELFStreamer clear's the assembler's e_flags. However, for
   // arm we manually set the ABI version on streamer creation, so
   // do the same here