[ELF] Allow TargetLayout descendants to control assignment sections to segments

[atanasyan]

Summary

The TargetLayout class puts two sections into the same segment if they have equal segment types and the same section flags (SHF_xxx). To be able to merge some sort of sections into the same segment we drop some flags before comparison. For example to merge string sections into Data segment we drop SHF_STRINGS and SHF_MERGE flags.

The patch allows TargetLayout descendants to drop some target specific section flags. MIPS target needs that to merge .MIPS.options section which has SHF_MIPS_NOSTRIP flag into the LOAD segment.

[ruiu]

LGTM

lib/ReaderWriter/ELF/Mips/MipsTargetLayout.h

87

I guess you can remove <ELFT> from this line.

lib/ReaderWriter/ELF/TargetLayout.cpp

334

nit: remove () around the _ctx.mergeRODataToTextSegment(). Also remove outermost () (the entire if condition is doubly parenthesized).

342

Remove this blank line.

[atanasyan]

lib/ReaderWriter/ELF/Mips/MipsTargetLayout.h

87

MipsTargetLayout is a template class and if I remove <ELFT> I get "'TargetLayout' is not a class, namespace, or enumeration" error.

[atanasyan]

Thanks for review.

Closed by commit rL235487.

lib/ReaderWriter/ELF/Mips/MipsTargetLayout.h

 
 protected:
   unique_bump_ptr<RelocationTable<ELFT>>
   createRelocationTable(StringRef name, int32_t order) override {
     return unique_bump_ptr<RelocationTable<ELFT>>(new (
         this->_allocator) MipsRelocationTable<ELFT>(this->_ctx, name, order));
   }
 
+  uint64_t getLookupSectionFlags(const OutputSection<ELFT> *os) const override {
+    uint64_t flags = TargetLayout<ELFT>::getLookupSectionFlags(os);
+    return flags & ~llvm::ELF::SHF_MIPS_NOSTRIP;
+  }
+
 private:
   MipsGOTSection<ELFT> *_gotSection;
   MipsPLTSection<ELFT> *_pltSection;
   uint64_t _gpAddr = 0;
   std::once_flag _gpOnce;
 };
 
 } // end namespace elf
 } // end namespace lld
 
 #endif

lib/ReaderWriter/ELF/TargetLayout.h

protected:
 
   /// \brief Create a new relocation table.
   virtual unique_bump_ptr<RelocationTable<ELFT>>
   createRelocationTable(StringRef name, int32_t order) {
     return unique_bump_ptr<RelocationTable<ELFT>>(
         new (_allocator) RelocationTable<ELFT>(_ctx, name, order));
   }
 
+  virtual uint64_t getLookupSectionFlags(const OutputSection<ELFT> *os) const;
+
 protected:
   llvm::BumpPtrAllocator _allocator;
   SectionMapT _sectionMap;
   OutputSectionMapT _outputSectionMap;
   AdditionalSegmentMapT _additionalSegmentMap;
   SegmentMapT _segmentMap;
   std::vector<Chunk<ELFT> *> _sections;
   std::vector<Segment<ELFT> *> _segments;

lib/ReaderWriter/ELF/TargetLayout.cpp

if (!outputSectionInsert.second) {
           OutputSection<ELFT>(section->outputSectionName());
       _outputSections.push_back(outputSection);
       outputSectionInsert.first->second = outputSection;
     }
     outputSection->appendSection(section);
   }
 }
 
+template <class ELFT>
+uint64_t
+TargetLayout<ELFT>::getLookupSectionFlags(const OutputSection<ELFT> *os) const {
+  uint64_t flags = os->flags();
+  if ((!(flags & llvm::ELF::SHF_WRITE)) && (_ctx.mergeRODataToTextSegment()))
+    flags &= ~llvm::ELF::SHF_EXECINSTR;
+
+  // Merge string sections into Data segment itself
+  flags &= ~(llvm::ELF::SHF_STRINGS | llvm::ELF::SHF_MERGE);
+
+  // Merge the TLS section into the DATA segment itself
+  flags &= ~(llvm::ELF::SHF_TLS);
+
+  return flags;
+}
+
 template <class ELFT> void TargetLayout<ELFT>::assignSectionsToSegments() {
   ScopedTask task(getDefaultDomain(), "assignSectionsToSegments");
   ELFLinkingContext::OutputMagic outputMagic = _ctx.getOutputMagic();
   // sort the sections by their order as defined by the layout
   sortInputSections();
 
   // Create output sections.
   createOutputSections();
for (auto section : osi->sections()) {
 
       // Get the segment type for the section
       int64_t segmentType = getSegmentType(section);
 
       osi->setHasSegment();
       section->setSegmentType(segmentType);
       StringRef segmentName = section->segmentKindToStr();
 
-      uint64_t lookupSectionFlag = osi->flags();
-      if ((!(lookupSectionFlag & llvm::ELF::SHF_WRITE)) &&
-          (_ctx.mergeRODataToTextSegment()))
-        lookupSectionFlag &= ~llvm::ELF::SHF_EXECINSTR;
-
-      // Merge string sections into Data segment itself
-      lookupSectionFlag &= ~(llvm::ELF::SHF_STRINGS | llvm::ELF::SHF_MERGE);
-
-      // Merge the TLS section into the DATA segment itself
-      lookupSectionFlag &= ~(llvm::ELF::SHF_TLS);
+      uint64_t lookupSectionFlag = getLookupSectionFlags(osi);
 
       Segment<ELFT> *segment;
       // We need a separate segment for sections that don't have
       // the segment type to be PT_LOAD
       if (segmentType != llvm::ELF::PT_LOAD) {
         const AdditionalSegmentKey key(segmentType, lookupSectionFlag);
         const std::pair<AdditionalSegmentKey, Segment<ELFT> *>
             additionalSegment(key, nullptr);

test/elf/Mips/mips-options-02.test

 # Check merging input .MIPS.options sections.
 
 # RUN: yaml2obj -format=elf -docnum 1 %s > %t1.o
 # RUN: yaml2obj -format=elf -docnum 2 %s > %t2.o
 # RUN: lld -flavor gnu -target mips64el -shared -o %t.so %t1.o %t2.o
 # RUN: llvm-readobj -s -dynamic-table %t.so | FileCheck -check-prefix=SEC %s
 # RUN: llvm-objdump -s -t %t.so | FileCheck -check-prefix=RAW %s
+# RUN: llvm-readobj -program-headers %t.so | FileCheck -check-prefix=PHDR %s
 
 # SEC:      Index: 1
 # SEC-NEXT: Name: .MIPS.options (1)
 # SEC-NEXT: Type: SHT_MIPS_OPTIONS (0x7000000D)
 # SEC-NEXT: Flags [ (0x8000002)
 # SEC-NEXT:   SHF_ALLOC (0x2)
 # SEC-NEXT:   SHF_MIPS_NOSTRIP (0x8000000)
 # SEC-NEXT: ]
 # SEC-NEXT: Address: 0x[[OPT_ADDR:[0-9A-F]+]]
 # SEC-NEXT: Offset: {{[0-9A-F]+}}
 # SEC-NEXT: Size: 40
 # SEC-NEXT: Link: 0
 # SEC-NEXT: Info: 0
 # SEC-NEXT: AddressAlignment: 8
 # SEC-NEXT: EntrySize: 1
 
 # SEC: DynamicSection [
 # SEC:   0x{{[0-9A-F]+}} MIPS_OPTIONS 0x[[OPT_ADDR]]
 
 # RAW:      Contents of section .MIPS.options:
-# RAW-NEXT:  1000 01280000 00000000 f0000001 00000000
-# RAW-NEXT:  1010 e0000002 d0000003 b0000004 c0000005
-# RAW-NEXT:  1020 f09f0000 00000000
+# RAW-NEXT:  {{[0-9a-f]+}} 01280000 00000000 f0000001 00000000
+# RAW-NEXT:  {{[0-9a-f]+}} e0000002 d0000003 b0000004 c0000005
+# RAW-NEXT:  {{[0-9a-f]+}} f08f0000 00000000
 
 # RAW: SYMBOL TABLE:
-# RAW: 0000000000009ff0 g *ABS* 00000000 _gp
+# RAW: 0000000000008ff0 g *ABS* 00000000 _gp
+
+# Check that %t.so contains only two PT_LOAD segments
+# PHDR:    ProgramHeaders
+# PHDR:      Type: PT_LOAD
+# PHDR:      Type: PT_LOAD
+# PHDR-NOT:  Type: PT_LOAD
+# PHDR:      Type: PT_DYNAMIC
+# PHDR:      Type: PT_NOTE
 
 # t1.o
 ---
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_MIPS

test/elf/Mips/mips-options-03.test

 # Check handling a zero-filled input .MIPS.options section.
 
 # RUN: yaml2obj -format=elf %s > %t.o
 # RUN: lld -flavor gnu -target mips64el -shared -o %t.so %t.o
 # RUN: llvm-objdump -s -t %t.so | FileCheck %s
 
 # CHECK:      Contents of section .MIPS.options:
-# CHECK-NEXT:  1000 01280000 00000000 00000000 00000000
-# CHECK-NEXT:  1010 00000000 00000000 00000000 00000000
-# CHECK-NEXT:  1020 f09f0000 00000000
+# CHECK-NEXT:  {{[0-9a-f]+}} 01280000 00000000 00000000 00000000
+# CHECK-NEXT:  {{[0-9a-f]+}} 00000000 00000000 00000000 00000000
+# CHECK-NEXT:  {{[0-9a-f]+}} f08f0000 00000000
 
 # CHECK: SYMBOL TABLE:
-# CHECK: 00009ff0 g *ABS* 00000000 _gp
+# CHECK: 00008ff0 g *ABS* 00000000 _gp
 
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_MIPS
   Flags:   [EF_MIPS_CPIC, EF_MIPS_PIC, EF_MIPS_ARCH_64R2]
 

test/elf/Mips/mips-options-04.test

 # Check that .MIPS.options sections from shared libraries do not affect
 # output .MIPS.options section content.
 
 # RUN: yaml2obj -format=elf -docnum 1 %s > %t.so.o
 # RUN: lld -flavor gnu -target mips64el -shared -o %t.so %t.so.o
 # RUN: yaml2obj -format=elf -docnum 2 %s > %t.exe.o
 # RUN: lld -flavor gnu -target mips64el -e T0 -o %t.exe %t.so %t.exe.o
 # RUN: llvm-objdump -s -t %t.exe | FileCheck %s
 
 # CHECK:      Contents of section .MIPS.options:
-# CHECK-NEXT:  120001000 01280000 00000000 44444444 00000000
-# CHECK-NEXT:  120001010 44444444 44444444 44444444 44444444
-# CHECK-NEXT:  120001020 f09f0020 01000000
+# CHECK-NEXT:  {{[0-9a-f]+}} 01280000 00000000 44444444 00000000
+# CHECK-NEXT:  {{[0-9a-f]+}} 44444444 44444444 44444444 44444444
+# CHECK-NEXT:  {{[0-9a-f]+}} f08f0020 01000000
 
 # CHECK: SYMBOL TABLE:
-# CHECK: 20009ff0 g *ABS* 00000000 _gp
+# CHECK: 20008ff0 g *ABS* 00000000 _gp
 
 # t.so.o
 ---
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_MIPS

test/elf/Mips/mips-options-05.test

 # Check that .MIPS.options section gets register usage mask from "used" files
 # only. In this test case we take only t2.o from liboptions.a and should not
 # add register usage masks from t1.o to the output .MIPS.options section.
 
 # RUN: yaml2obj -format=elf -docnum 1 %s > %t1.o
 # RUN: yaml2obj -format=elf -docnum 2 %s > %t2.o
 # RUN: llvm-ar q %T/liboptions.a %t1.o %t2.o
 # RUN: yaml2obj -format=elf -docnum 3 %s > %t3.o
 # RUN: lld -flavor gnu -target mips64el -e T0 -o %t.exe %t3.o -L%T -loptions
 # RUN: llvm-objdump -s -t %t.exe | FileCheck %s
 
 # CHECK:      Contents of section .MIPS.options:
-# CHECK-NEXT:  120001000 01280000 00000000 66666666 00000000
-# CHECK-NEXT:  120001010 66666666 66666666 66666666 66666666
-# CHECK-NEXT:  120001020 f09f0020 01000000
+# CHECK-NEXT:  {{[0-9a-f]+}} 01280000 00000000 66666666 00000000
+# CHECK-NEXT:  {{[0-9a-f]+}} 66666666 66666666 66666666 66666666
+# CHECK-NEXT:  {{[0-9a-f]+}} f08f0020 01000000
 
 # CHECK: SYMBOL TABLE:
-# CHECK: 20009ff0 g *ABS* 00000000 _gp
+# CHECK: 20008ff0 g *ABS* 00000000 _gp
 
 # t1.o
 ---
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_MIPS

test/elf/Mips/mips-options-gp0.test

 # Check reading GP0 value from .MIPS.options section
 #
 # RUN: yaml2obj -format=elf %s > %t.o
 # RUN: lld -flavor gnu -target mips64el -e G1 -shared -o %t.so %t.o
 # RUN: llvm-readobj -symbols %t.so | FileCheck -check-prefix=SYM %s
 # RUN: llvm-objdump -s %t.so | FileCheck -check-prefix=SEC %s
 
 # SYM:      Name: L1
-# SYM-NEXT: Value: 0x1A4
+# SYM-NEXT: Value: 0x194
 # SYM-NEXT: Size: 4
 # SYM-NEXT: Binding: Local (0x0)
 # SYM-NEXT: Type: Function (0x2)
 # SYM-NEXT: Other: 0
 # SYM-NEXT: Section: .text (0x5)
 
 # SYM:      Name: _gp
-# SYM-NEXT: Value: 0x9FF0
+# SYM-NEXT: Value: 0x8FF0
 # SYM-NEXT: Size: 0
 # SYM-NEXT: Binding: Global (0x1)
 # SYM-NEXT: Type: Object (0x1)
 # SYM-NEXT: Other: 0
 # SYM-NEXT: Section: Absolute (0xFFF1)
 
-# 0xffff71b4 == 0x0 (addend) + 0x01A4 (L1) + 0x1000 (GP0) - 0x9ff0 (_gp)
+# 0xffff81a4 == 0x0 (addend) + 0x0194 (L1) + 0x1000 (GP0) - 0x8ff0 (_gp)
 # SEC:      Contents of section .rodata:
-# SEC-NEXT:  01ac b471ffff 00000000 00000000 00000000
+# SEC-NEXT:  {{[0-9a-f]+}} a481ffff 00000000 00000000 00000000
 
 !ELF
 FileHeader:
   Class:    ELFCLASS64
   Data:     ELFDATA2LSB
   Type:     ET_REL
   Machine:  EM_MIPS
   Flags:    [ EF_MIPS_NOREORDER, EF_MIPS_PIC, EF_MIPS_CPIC, EF_MIPS_ARCH_64R2 ]