[mips] Add SHF_MIPS_GPREL flag to the MIPS .sbss and .sdata sections

[atanasyan]

Summary

MIPS ABI states that .sbss and .sdata sections must have SHF_MIPS_GPREL flag. See Figure 4–7 on page 69 in the following document: ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf.

[khemant]

tools/llvm-readobj/ELFDumper.cpp

803

Probably I am not understanding this right, this flag is in SHF_MASKPROC bit fields. Shouldn't the flag printer (for instance in section printer) be checking processor printing the section flags ? Adding it here makes any processor that may use the same field not be able to use the enum string other than SHF_MIPS_GPREL.

[atanasyan]

tools/llvm-readobj/ELFDumper.cpp

803

Good point, thanks. I will fix it.

[atanasyan]

I implemented support for target specific ELF section flags in a separate commit r258334. Now this patch contains MIPS specific code only.

[atanasyan]

Ping?

[dsanders]

LGTM with a test for .sbss too

lib/Target/Mips/MipsTargetObjectFile.cpp

ExternSData("mextern-sdata", cl::Hidden,
                      "current object."),
             cl::init(true));
 
 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
   InitializeELF(TM.Options.UseInitArray);
 
   SmallDataSection = getContext().getELFSection(
-      ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
+      ".sdata", ELF::SHT_PROGBITS,
+      ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_MIPS_GPREL);
 
   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
-                                               ELF::SHF_WRITE | ELF::SHF_ALLOC);
+                                               ELF::SHF_WRITE | ELF::SHF_ALLOC |
+                                                   ELF::SHF_MIPS_GPREL);
   this->TM = &static_cast<const MipsTargetMachine &>(TM);
 }
 
 // A address must be loaded from a small section if its size is less than the
 // small section size threshold. Data in this section must be addressed using
 // gp_rel operator.
 static bool IsInSmallSection(uint64_t Size) {
   // gcc has traditionally not treated zero-sized objects as small data, so this

test/CodeGen/Mips/mips-shf-gprel.ll

+; Check that .sdata section has SHF_MIPS_GPREL flag.
+
+; RUN: llc -mips-ssection-threshold=16 -mgpopt -mattr=noabicalls \
+; RUN:     -relocation-model=static -march=mips -o - %s -filetype=obj \
+; RUN:   | llvm-readobj -s | FileCheck %s
+
+@data = global [4 x i32] [i32 1, i32 2, i32 3, i32 4], align 4
+
+; CHECK:      Name: .sdata
+; CHECK-NEXT: Type: SHT_PROGBITS
+; CHECK-NEXT: Flags [ (0x10000003)
+; CHECK-NEXT:   SHF_ALLOC
+; CHECK-NEXT:   SHF_MIPS_GPREL
+; CHECK-NEXT:   SHF_WRITE
+; CHECK-NEXT: ]

tools/llvm-readobj/ELFDumper.cpp

static const EnumEntry<unsigned> ElfSectionFlags[] = {
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_INFO_LINK       ),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_LINK_ORDER      ),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_OS_NONCONFORMING),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_GROUP           ),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_TLS             ),
   LLVM_READOBJ_ENUM_ENT(ELF, XCORE_SHF_CP_SECTION),
   LLVM_READOBJ_ENUM_ENT(ELF, XCORE_SHF_DP_SECTION),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_MIPS_NOSTRIP    ),
+  LLVM_READOBJ_ENUM_ENT(ELF, SHF_MIPS_GPREL      ),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_AMDGPU_HSA_GLOBAL),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_AMDGPU_HSA_READONLY),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_AMDGPU_HSA_CODE),
   LLVM_READOBJ_ENUM_ENT(ELF, SHF_AMDGPU_HSA_AGENT)
 };
 
 static const char *getElfSegmentType(unsigned Arch, unsigned Type) {
   // Check potentially overlapped processor-specific