[PowerPC] Support parsing GNU attributes in MC

[qiucf]

Summary

According to GNU as documentation, PowerPC supports two kinds of .gnu_attribute tag to represent the vector and float ABI type in the object file. (https://sourceware.org/binutils/docs-2.35/as/GNU-Object-Attributes.html) Some linkers like GNU ld respects the attribute and will prevent objects with conflicting ABIs being linked.

Commit 7aef993 already did the work for generally parse and emit GNU attributes information. This patch is the first step to enable support of the attribute in LLVM PowerPC, enabling it for PowerPC targets, otherwise llvm-mc raises error when seeing the attribute section.

[qiucf]

Ping.

[jsji]

LGTM. Thanks for adding this feature.

llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp

class PPCAsmParser : public MCTargetAsmParser {
 
   bool ParseOperand(OperandVector &Operands);
 
   bool ParseDirectiveWord(unsigned Size, AsmToken ID);
   bool ParseDirectiveTC(unsigned Size, AsmToken ID);
   bool ParseDirectiveMachine(SMLoc L);
   bool ParseDirectiveAbiVersion(SMLoc L);
   bool ParseDirectiveLocalEntry(SMLoc L);
+  bool ParseGNUAttribute(SMLoc L);
 
   bool MatchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
                                OperandVector &Operands, MCStreamer &Out,
                                uint64_t &ErrorInfo,
                                bool MatchingInlineAsm) override;
 
   void ProcessInstruction(MCInst &Inst, const OperandVector &Ops);
 
bool PPCAsmParser::ParseDirective(AsmToken DirectiveID) {
   else if (IDVal == ".tc")
     ParseDirectiveTC(isPPC64() ? 8 : 4, DirectiveID);
   else if (IDVal == ".machine")
     ParseDirectiveMachine(DirectiveID.getLoc());
   else if (IDVal == ".abiversion")
     ParseDirectiveAbiVersion(DirectiveID.getLoc());
   else if (IDVal == ".localentry")
     ParseDirectiveLocalEntry(DirectiveID.getLoc());
+  else if (IDVal.startswith(".gnu_attribute"))
+    ParseGNUAttribute(DirectiveID.getLoc());
   else
     return true;
   return false;
 }
 
 /// ParseDirectiveWord
 ///  ::= .word [ expression (, expression)* ]
 bool PPCAsmParser::ParseDirectiveWord(unsigned Size, AsmToken ID) {
bool PPCAsmParser::ParseDirectiveLocalEntry(SMLoc L) {
   PPCTargetStreamer *TStreamer = static_cast<PPCTargetStreamer *>(
       getParser().getStreamer().getTargetStreamer());
   if (TStreamer != nullptr)
     TStreamer->emitLocalEntry(Sym, Expr);
 
   return false;
 }
 
+bool PPCAsmParser::ParseGNUAttribute(SMLoc L) {
+  int64_t Tag;
+  int64_t IntegerValue;
+  if (!getParser().parseGNUAttribute(L, Tag, IntegerValue))
+    return false;
+
+  getParser().getStreamer().emitGNUAttribute(Tag, IntegerValue);
 
+  return true;
+}
 
 /// Force static initialization.
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializePowerPCAsmParser() {
   RegisterMCAsmParser<PPCAsmParser> A(getThePPC32Target());
   RegisterMCAsmParser<PPCAsmParser> B(getThePPC32LETarget());
   RegisterMCAsmParser<PPCAsmParser> C(getThePPC64Target());
   RegisterMCAsmParser<PPCAsmParser> D(getThePPC64LETarget());
 }

llvm/test/MC/PowerPC/gnu-attribute.s

+# RUN: llvm-mc -triple powerpc64-unknown-linux-gnu < %s | FileCheck %s
+# RUN: llvm-mc -triple powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+
+  .text
+add:
+  add 3, 4, 3
+  blr
+  .gnu_attribute 4, 13
+
+# CHECK-LABEL: add:
+# CHECK: .gnu_attribute 4, 13