[MC][ELF] Use SHF_SUNW_NODISCARD instead of SHF_GNU_RETAIN on Solaris

[ro]

Summary

As requested in D107955, this patch splits off the MC and CodeGen parts and adds a testcase.

Tested on sparcv9-sun-solaris2.11, amd64-pc-solaris2.11, and x86_64-pc-linux-gnu.

[MaskRay]

LGTM.

llvm/lib/MC/MCSectionELF.cpp

108

Maybe conciser: // Print OS-specific flags.`

llvm/test/CodeGen/X86/elf-retain.ll

6

[ro]

llvm/lib/MC/MCSectionELF.cpp

108

I'd rather keep if for consistency with the next comment.

[ro]

Comment and whitespace fixes.

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

calcUniqueIDUpdateFlagsAndSize(const GlobalObject *GO, StringRef SectionName,
   // MD_associated in a unique section.
   const bool Associated = GO->getMetadata(LLVMContext::MD_associated);
   if (Associated) {
     Flags |= ELF::SHF_LINK_ORDER;
     return NextUniqueID++;
   }
 
   if (Retain) {
-    if ((Ctx.getAsmInfo()->useIntegratedAssembler() ||
-         Ctx.getAsmInfo()->binutilsIsAtLeast(2, 36)) &&
-        !TM.getTargetTriple().isOSSolaris())
+    if (TM.getTargetTriple().isOSSolaris())
+      Flags |= ELF::SHF_SUNW_NODISCARD;
+    else if (Ctx.getAsmInfo()->useIntegratedAssembler() ||
+             Ctx.getAsmInfo()->binutilsIsAtLeast(2, 36))
       Flags |= ELF::SHF_GNU_RETAIN;
     return NextUniqueID++;
   }
 
   // If two symbols with differing sizes end up in the same mergeable section
   // that section can be assigned an incorrect entry size. To avoid this we
   // usually put symbols of the same size into distinct mergeable sections with
   // the same name. Doing so relies on the ",unique ," assembly feature. This
static MCSection *selectELFSectionForGlobal(
     MCContext &Ctx, const GlobalObject *GO, SectionKind Kind, Mangler &Mang,
     const TargetMachine &TM, bool Retain, bool EmitUniqueSection,
     unsigned Flags, unsigned *NextUniqueID) {
   const MCSymbolELF *LinkedToSym = getLinkedToSymbol(GO, TM);
   if (LinkedToSym) {
     EmitUniqueSection = true;
     Flags |= ELF::SHF_LINK_ORDER;
   }
-  if (Retain &&
-      (Ctx.getAsmInfo()->useIntegratedAssembler() ||
-       Ctx.getAsmInfo()->binutilsIsAtLeast(2, 36)) &&
-      !TM.getTargetTriple().isOSSolaris()) {
+  if (Retain) {
+    if (TM.getTargetTriple().isOSSolaris()) {
+      EmitUniqueSection = true;
+      Flags |= ELF::SHF_SUNW_NODISCARD;
+    } else if (Ctx.getAsmInfo()->useIntegratedAssembler() ||
+               Ctx.getAsmInfo()->binutilsIsAtLeast(2, 36)) {
       EmitUniqueSection = true;
       Flags |= ELF::SHF_GNU_RETAIN;
     }
+  }
 
   MCSectionELF *Section = selectELFSectionForGlobal(
       Ctx, GO, Kind, Mang, TM, EmitUniqueSection, Flags,
       NextUniqueID, LinkedToSym);
   assert(Section->getLinkedToSymbol() == LinkedToSym);
   return Section;
 }
 

llvm/lib/MC/MCParser/ELFAsmParser.cpp

if (PrevLoc.getPointer() + CurSize != getTok().getLoc().getPointer())
       break;
   }
   if (Size == 0)
     return true;
 
   return false;
 }
 
-static unsigned parseSectionFlags(StringRef flagsStr, bool *UseLastGroup) {
+static unsigned parseSectionFlags(const Triple &TT, StringRef flagsStr,
+                                  bool *UseLastGroup) {
   unsigned flags = 0;
 
   // If a valid numerical value is set for the section flag, use it verbatim
   if (!flagsStr.getAsInteger(0, flags))
     return flags;
 
   for (char i : flagsStr) {
     switch (i) {
case 'y':
       break;
     case 's':
       flags |= ELF::SHF_HEX_GPREL;
       break;
     case 'G':
       flags |= ELF::SHF_GROUP;
       break;
     case 'R':
+      if (TT.isOSSolaris())
+        flags |= ELF::SHF_SUNW_NODISCARD;
+      else
         flags |= ELF::SHF_GNU_RETAIN;
       break;
     case '?':
       *UseLastGroup = true;
       break;
     default:
       return -1U;
     }
   }
if (getLexer().is(AsmToken::Comma)) {
     if (getLexer().isNot(AsmToken::String)) {
       if (!getContext().getAsmInfo()->usesSunStyleELFSectionSwitchSyntax()
           || getLexer().isNot(AsmToken::Hash))
         return TokError("expected string in directive");
       extraFlags = parseSunStyleSectionFlags();
     } else {
       StringRef FlagsStr = getTok().getStringContents();
       Lex();
-      extraFlags = parseSectionFlags(FlagsStr, &UseLastGroup);
+      extraFlags = parseSectionFlags(getContext().getTargetTriple(), FlagsStr,
+                                     &UseLastGroup);
     }
 
     if (extraFlags == -1U)
       return TokError("unknown flag");
     Flags |= extraFlags;
 
     bool Mergeable = Flags & ELF::SHF_MERGE;
     bool Group = Flags & ELF::SHF_GROUP;

llvm/lib/MC/MCSectionELF.cpp

if (Flags & ELF::SHF_STRINGS)
     OS << 'S';
   if (Flags & ELF::SHF_TLS)
     OS << 'T';
   if (Flags & ELF::SHF_LINK_ORDER)
     OS << 'o';
   if (Flags & ELF::SHF_GNU_RETAIN)
     OS << 'R';
 
+  // If there are os-specific flags, print them.
+  if (T.isOSSolaris())
+    if (Flags & ELF::SHF_SUNW_NODISCARD)
+      OS << 'R';
+
   // If there are target-specific flags, print them.
   Triple::ArchType Arch = T.getArch();
   if (Arch == Triple::xcore) {
     if (Flags & ELF::XCORE_SHF_CP_SECTION)
       OS << 'c';
     if (Flags & ELF::XCORE_SHF_DP_SECTION)
       OS << 'd';
   } else if (T.isARM() || T.isThumb()) {

llvm/test/CodeGen/X86/elf-retain.ll

 ;; Place a global object in the llvm.used list in a unique section with the SHF_GNU_RETAIN flag.
 ; RUN: llc -mtriple=x86_64 < %s | FileCheck %s
 ; RUN: llc -mtriple=x86_64 -data-sections=1 < %s | FileCheck %s
 ; RUN: llc -mtriple=x86_64 -no-integrated-as -binutils-version=2.36 < %s | FileCheck %s
 ; RUN: llc -mtriple=x86_64 -no-integrated-as -binutils-version=2.35 < %s | FileCheck %s --check-prefix=OLDGAS
+;; Solaris uses the equivalent SHF_SUNW_NODISCARD flag, also represented as "R".
+; RUN: llc -mtriple=x86_64-solaris < %s | FileCheck %s
 
 ; RUN: llc -mtriple=x86_64 -data-sections=1 -unique-section-names=0 < %s | FileCheck %s --check-prefix=NOUNIQUE
 
 @llvm.used = appending global [10 x i8*] [
   i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @fb to i8*), i8* bitcast (void ()* @fc to i8*),
   i8* bitcast (i32* @ga to i8*), i8* bitcast (i32* @gb to i8*), i8* bitcast (i32* @gc to i8*), i8* bitcast (i32* @gd to i8*), i8* bitcast (i32* @ge to i8*),
   i8* bitcast (i32* @aa to i8*), i8* bitcast (i32* @ab to i8*) ], section "llvm.metadata"
 

llvm/test/MC/ELF/section-gnu.s

 # REQUIRES: aarch64-registered-target
 # RUN: llvm-mc -triple=x86_64 %s | FileCheck %s --check-prefix=ASM
-# RUN: llvm-mc -filetype=obj -triple=x86_64 %s | llvm-readobj -hS - | FileCheck %s --check-prefixes=GNU,OBJ
-# RUN: llvm-mc -filetype=obj -triple=aarch64-freebsd %s | llvm-readobj -hS - | FileCheck %s --check-prefixes=FREEBSD,OBJ
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s | llvm-readobj -hS - | FileCheck %s --check-prefixes=GNU,OBJ,OBJ-GNU
+# RUN: llvm-mc -filetype=obj -triple=aarch64-freebsd %s | llvm-readobj -hS - | FileCheck %s --check-prefixes=FREEBSD,OBJ,OBJ-GNU
+# RUN: llvm-mc -filetype=obj -triple=x86_64-solaris %s | llvm-readobj -hS - | FileCheck %s --check-prefixes=SOLARIS,OBJ,OBJ-SOLARIS
 
 # ASM: .section retain,"aR",@progbits
 
 ## ELFOSABI_NONE is changed to ELFOSABI_GNU. Other OSABI values are unchanged.
 # GNU:      OS/ABI: GNU/Linux
 # FREEBSD:  OS/ABI: FreeBSD
+# SOLARIS:  OS/ABI: Solaris
 
-# OBJ:      Name: retain
-# OBJ-NEXT: Type: SHT_PROGBITS
-# OBJ-NEXT: Flags [
-# OBJ-NEXT:   SHF_ALLOC
-# OBJ-NEXT:   SHF_GNU_RETAIN
-# OBJ-NEXT: ]
+# OBJ:              Name: retain
+# OBJ-NEXT:         Type: SHT_PROGBITS
+# OBJ-NEXT:         Flags [
+# OBJ-NEXT:           SHF_ALLOC
+# OBJ-GNU-NEXT:       SHF_GNU_RETAIN
+# OBJ-SOLARIS-NEXT:   SHF_SUNW_NODISCARD
+# OBJ-NEXT:         ]
 
 .section retain,"aR",@progbits