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

[Eric Astor via Phabricator via llvm-commits]

epastor created this revision.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
epastor updated this revision to Diff 231159.
epastor added a comment.

- Fix comment.


Allows assembly files targeting 32-bit Windows to be linked with /safeseh.

For example, Boost Context distributes GNU-syntax assembly files for its primitives, but if assembled with clang, neither link.exe nor lld-link can link them with /safeseh.


Repository:
  rG LLVM Github Monorepo

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"
@@ -887,6 +888,32 @@
   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();
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D70757.231159.patch
Type: text/x-patch
Size: 1833 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20191127/41098bcc/attachment.bin>