[PATCH] D70757: [ms] Add @feat.00 magic symbol to COFF object files from AsmParser

[Eric Astor via Phabricator via llvm-commits]

epastor updated this revision to Diff 231290.
epastor added a comment.

- Restrict @feat.00 symbol creation to the initial text segment.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D70757/new/

https://reviews.llvm.org/D70757

Files:
  llvm/lib/MC/MCParser/AsmParser.cpp


Index: llvm/lib/MC/MCParser/AsmParser.cpp
===================================================================
--- llvm/lib/MC/MCParser/AsmParser.cpp
+++ llvm/lib/MC/MCParser/AsmParser.cpp
@@ -21,6 +21,7 @@
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/BinaryFormat/COFF.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/DebugInfo/CodeView/SymbolRecord.h"
 #include "llvm/MC/MCAsmInfo.h"
@@ -884,9 +885,36 @@
 
 bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
   // Create the initial section, if requested.
-  if (!NoInitialTextSection)
+  if (!NoInitialTextSection) {
     Out.InitSections(false);
 
+    if (Ctx.getObjectFileInfo()->getObjectFileType() ==
+        MCObjectFileInfo::IsCOFF) {
+      // Emit an absolute @feat.00 symbol.  This appears to be some kind of
+      // compiler features bitfield read by link.exe.
+      MCSymbol *Feat00Sym = getContext().getOrCreateSymbol("@feat.00");
+      getStreamer().BeginCOFFSymbolDef(Feat00Sym);
+      getStreamer().EmitCOFFSymbolStorageClass(COFF::IMAGE_SYM_CLASS_STATIC);
+      getStreamer().EmitCOFFSymbolType(COFF::IMAGE_SYM_DTYPE_NULL);
+      getStreamer().EndCOFFSymbolDef();
+      int64_t Feat00Flags = 0;
+
+      if (getContext().getObjectFileInfo()->getTargetTriple().getArch() ==
+          Triple::x86) {
+        // According to the PE-COFF spec, the LSB of this value marks the object
+        // for "registered SEH".  This means that all SEH handler entry points
+        // must be registered in .sxdata.  Use of any unregistered handlers will
+        // cause the process to terminate immediately.  LLVM does not know how
+        // to register any SEH handlers, so its object files should be safe.
+        Feat00Flags |= 1;
+      }
+
+      getStreamer().EmitSymbolAttribute(Feat00Sym, MCSA_Global);
+      getStreamer().EmitAssignment(
+          Feat00Sym, MCConstantExpr::create(Feat00Flags, getContext()));
+    }
+  }
+
   // Prime the lexer.
   Lex();
 


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