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

Summary:
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.

Reviewers: rafael, bkramer

Reviewed By: bkramer

CC: llvm-commits

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190768 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 21 insertions, 3 deletions

diff --git a/lib/MC/MCParser/ELFAsmParser.cpp b/lib/MC/MCParser/ELFAsmParser.cpp
index 964f915..67b0e5d 100644
--- a/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/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;
 
@@ -278,7 +279,7 @@ static SectionKind computeSectionKind(unsigned Flags) {
   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++) {
@@ -310,6 +311,9 @@ static int parseSectionFlags(StringRef flagsStr) {
     case 'G':
       flags |= ELF::SHF_GROUP;
       break;
+    case '?':
+      *UseLastGroup = true;
+      break;
     default:
       return -1;
     }
@@ -351,6 +355,7 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush) {
   StringRef GroupName;
   unsigned Flags = 0;
   const MCExpr *Subsection = 0;
+  bool UseLastGroup = false;
 
   // Set the defaults first.
   if (SectionName == ".fini" || SectionName == ".init" ||
@@ -376,13 +381,16 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush) {
     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)
@@ -460,6 +468,16 @@ EndStmt:
       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,
diff --git a/test/MC/ELF/comdat.s b/test/MC/ELF/comdat.s
index 6dbe583..3e4a001 100644
--- a/test/MC/ELF/comdat.s
+++ b/test/MC/ELF/comdat.s
@@ -82,7 +82,7 @@
 g1:
         nop
 
-        .section	.bar,"axG",@progbits,g1,comdat
+        .section	.bar,"ax?",@progbits
         nop
 
         .section	.zed,"axG",@progbits,g2,comdat