[PATCH] MC: Add support for '?' flags in .section directives

[David Majnemer]

Hi rafael,

The '?' flag uses the last section group if the last had a section
group.  We treat combining an explicit section group and the '?' as a
hard error.

This fixes PR17198.

http://llvm-reviews.chandlerc.com/D1686

Files:
  lib/MC/MCParser/ELFAsmParser.cpp
  test/MC/ELF/comdat.s

Index: lib/MC/MCParser/ELFAsmParser.cpp
===================================================================
--- lib/MC/MCParser/ELFAsmParser.cpp
+++ lib/MC/MCParser/ELFAsmParser.cpp
@@ -16,6 +16,7 @@
 #include "llvm/MC/MCParser/MCAsmLexer.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/ELF.h"
 using namespace llvm;
 
@@ -279,7 +280,7 @@
   return SectionKind::getDataRel();
 }
 
-static int parseSectionFlags(StringRef flagsStr) {
+static int parseSectionFlags(StringRef flagsStr, bool *UseLastGroup) {
   int flags = 0;
 
   for (unsigned i = 0; i < flagsStr.size(); i++) {
@@ -311,6 +312,9 @@
     case 'G':
       flags |= ELF::SHF_GROUP;
       break;
+    case '?':
+      *UseLastGroup = true;
+      break;
     default:
       return -1;
     }
@@ -352,6 +356,7 @@
   StringRef GroupName;
   unsigned Flags = 0;
   const MCExpr *Subsection = 0;
+  bool UseLastGroup = false;
 
   // Set the defaults first.
   if (SectionName == ".fini" || SectionName == ".init" ||
@@ -377,13 +382,16 @@
     StringRef FlagsStr = getTok().getStringContents();
     Lex();
 
-    int extraFlags = parseSectionFlags(FlagsStr);
+    int extraFlags = parseSectionFlags(FlagsStr, &UseLastGroup);
     if (extraFlags < 0)
       return TokError("unknown flag");
     Flags |= extraFlags;
 
     bool Mergeable = Flags & ELF::SHF_MERGE;
     bool Group = Flags & ELF::SHF_GROUP;
+    if (Group && UseLastGroup)
+      return TokError("Section cannot specifiy a group name while also acting "
+                      "as a member of the last group");
 
     if (getLexer().isNot(AsmToken::Comma)) {
       if (Mergeable)
@@ -461,6 +469,16 @@
       return TokError("unknown section type");
   }
 
+  if (UseLastGroup) {
+    MCSectionSubPair CurrentSection = getStreamer().getCurrentSection();
+    if (const MCSectionELF *Section =
+            cast_or_null<MCSectionELF>(CurrentSection.first))
+      if (const MCSymbol *Group = Section->getGroup()) {
+        GroupName = Group->getName();
+        Flags |= ELF::SHF_GROUP;
+      }
+  }
+
   SectionKind Kind = computeSectionKind(Flags);
   getStreamer().SwitchSection(getContext().getELFSection(SectionName, Type,
                                                          Flags, Kind, Size,
Index: test/MC/ELF/comdat.s
===================================================================
--- test/MC/ELF/comdat.s
+++ test/MC/ELF/comdat.s
@@ -82,7 +82,7 @@
 g1:
         nop
 
-        .section	.bar,"axG", at progbits,g1,comdat
+        .section	.bar,"ax?", at progbits
         nop
 
         .section	.zed,"axG", at progbits,g2,comdat
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