[PATCH] D45778: [COFF] Mark images with no exception handlers for /safeseh

[Reid Kleckner via Phabricator via llvm-commits]

rnk created this revision.
rnk added reviewers: ruiu, mstorsjo.

DLLs and executables with no exception handlers need to be marked with
IMAGE_DLL_CHARACTERISTICS_NO_SEH, even if they have a load config.

Discovered here when building Chromium with LLD on Windows:
https://crbug.com/833951


https://reviews.llvm.org/D45778

Files:
  lld/COFF/Writer.cpp
  lld/test/COFF/safeseh.s


Index: lld/test/COFF/safeseh.s
===================================================================
--- lld/test/COFF/safeseh.s
+++ lld/test/COFF/safeseh.s
@@ -6,6 +6,7 @@
 
 # __safe_se_handler_table needs to be relocated against ImageBase.
 # check that the relocation is present.
+#
 # CHECK-NOGC-NOT: IMAGE_DLL_CHARACTERISTICS_NO_SEH
 # CHECK-NOGC: BaseReloc [
 # CHECK-NOGC:   Entry {
@@ -19,9 +20,14 @@
 # CHECK-NOGC-NEXT:   0x401006
 # CHECK-NOGC-NEXT: ]
 
-# Without the SEH table, the address is absolute, so check that we do
-# not have a relocation for it.
-# CHECK-GC-NOT: IMAGE_DLL_CHARACTERISTICS_NO_SEH
+# If we enable GC, the exception handler should be removed, and we should add
+# the DLL characteristic flag that indicates that there are no exception
+# handlers in this DLL. The exception handler table in the load config should
+# be empty and there should be no relocations for it.
+#
+# CHECK-GC: Characteristics [
+# CHECK-GC:   IMAGE_DLL_CHARACTERISTICS_NO_SEH
+# CHECK-GC: ]
 # CHECK-GC: BaseReloc [
 # CHECK-GC-NEXT: ]
 # CHECK-GC: LoadConfig [
Index: lld/COFF/Writer.cpp
===================================================================
--- lld/COFF/Writer.cpp
+++ lld/COFF/Writer.cpp
@@ -185,8 +185,7 @@
   IdataContents Idata;
   DelayLoadContents DelayIdata;
   EdataContents Edata;
-  RVATableChunk *GuardFidsTable = nullptr;
-  RVATableChunk *SEHTable = nullptr;
+  bool HasSafeExceptionHandlers = false;
 
   DebugDirectoryChunk *DebugDirectory = nullptr;
   std::vector<Chunk *> DebugRecords;
@@ -828,8 +827,7 @@
     PE->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_ISOLATION;
   if (Config->GuardCF != GuardCFLevel::Off)
     PE->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_GUARD_CF;
-  if (Config->Machine == I386 && !SEHTable &&
-      !Symtab->findUnderscore("_load_config_used"))
+  if (Config->Machine == I386 && !HasSafeExceptionHandlers)
     PE->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_SEH;
   if (Config->TerminalServerAware)
     PE->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_TERMINAL_SERVER_AWARE;
@@ -944,6 +942,8 @@
     markSymbolsForRVATable(File, File->getSXDataChunks(), Handlers);
   }
 
+  HasSafeExceptionHandlers = !Handlers.empty();
+
   maybeAddRVATable(std::move(Handlers), "__safe_se_handler_table",
                    "__safe_se_handler_count");
 }


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