[ELF2] Add initial MIPS support

[atanasyan]

Summary

Besides a trivial MIPS support the patch introduces new TargetInfo class member getDefEntryName() to override default name of the entry symbol. MIPS uses __start for that.

[ruiu]

LGTM with a nit.

ELF/SymbolTable.cpp

50–51 ↗

(On Diff #35910)

These cases need to be sorted by ASCIIbetical order, but yeah, that should be done in a different patch.

ELF/Target.h

38 ↗

(On Diff #35910)

It's probably a matter of taste, but I'd name DefaultEntry instead of DefEntryName. (Because the linker mainly handles names, "name" tend to be added everywhere, so I wouldn't add that in the first place.)

[davide]

This seems correct. Minor comments below.

ELF/Target.h

25 ↗

(On Diff #35910)

Can we keep the getter sorted?

test/elf2/basic-mips.s

5 ↗

(On Diff #35910)

Extra \n

8 ↗

(On Diff #35910)

Can you please add a comment explaining what this test does (as we do on other archs)?

[atanasyan]

ELF/SymbolTable.cpp

50–51 ↗

(On Diff #35910)

The case labels are sorted already. Do you want to sort them by xxxTargetInfo class names?

test/elf2/basic-mips.s

5 ↗

(On Diff #35910)

I think it is better to separate "running" instructions (RUN) from "configuration" instructions (REQUIRES).

[ruiu]

ELF/SymbolTable.cpp

50–51 ↗

(On Diff #35910)

Ah, I didn't notice that. We are using different names for valid reasons (386TargetInfo is not even a valid name!) Thank you for pointing that out.

lld/trunk/ELF/SymbolTable.cpp

 static TargetInfo *createTarget(uint16_t EMachine) {
   switch (EMachine) {
   case EM_386:
     return new X86TargetInfo();
   case EM_AARCH64:
     return new AArch64TargetInfo();
   case EM_ARM:
     return new ARMTargetInfo();
+  case EM_MIPS:
+    return new MipsTargetInfo();
   case EM_PPC:
     return new PPCTargetInfo();
   case EM_PPC64:
     return new PPC64TargetInfo();
   case EM_X86_64:
     return new X86_64TargetInfo();
   }
   error("Unknown target machine");
void SymbolTable::addSyntheticSym(StringRef Name, OutputSection<ELFT> &Section,
   auto Sym = new (Alloc) DefinedSynthetic<ELFT>(Name, *ESym, Section);
   resolve<ELFT>(Sym);
 }
 
 template <class ELFT> void SymbolTable::init(uint16_t EMachine) {
   Target.reset(createTarget(EMachine));
   if (Config->Shared)
     return;
-  EntrySym = new (Alloc) Undefined<ELFT>("_start", Undefined<ELFT>::Synthetic);
+  EntrySym = new (Alloc)
+      Undefined<ELFT>(Target->getDefaultEntry(), Undefined<ELFT>::Synthetic);
   resolve<ELFT>(EntrySym);
 
   // In the assembly for 32 bit x86 the _GLOBAL_OFFSET_TABLE_ symbol is magical
   // and is used to produce a R_386_GOTPC relocation.
   // The R_386_GOTPC relocation value doesn't actually depend on the
   // symbol value, so it could use an index of STN_UNDEF which, according to the
   // spec, means the symbol value is 0.
   // Unfortunately both gas and MC keep the _GLOBAL_OFFSET_TABLE_ symbol in

lld/trunk/ELF/Target.h

 //===- Target.h -------------------------------------------------*- C++ -*-===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLD_ELF_TARGET_H
 #define LLD_ELF_TARGET_H
 
+#include "llvm/ADT/StringRef.h"
+
 #include <memory>
 
 namespace lld {
 namespace elf2 {
 class SymbolBody;
 
 class TargetInfo {
 public:
+  llvm::StringRef getDefaultEntry() const { return DefaultEntry; }
   unsigned getPCRelReloc() const { return PCRelReloc; }
   unsigned getGotReloc() const { return GotReloc; }
   virtual void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                              uint64_t PltEntryAddr) const = 0;
   virtual bool relocNeedsGot(uint32_t Type) const = 0;
   virtual bool relocNeedsPlt(uint32_t Type) const = 0;
   virtual void relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                            uint64_t BaseAddr, uint64_t SymVA) const = 0;
 
   virtual ~TargetInfo();
 
 protected:
   unsigned PCRelReloc;
   unsigned GotReloc;
+  llvm::StringRef DefaultEntry = "_start";
 };
 
 class X86TargetInfo final : public TargetInfo {
 public:
   X86TargetInfo();
   void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                      uint64_t PltEntryAddr) const override;
   bool relocNeedsGot(uint32_t Type) const override;
public:
   void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                      uint64_t PltEntryAddr) const override;
   bool relocNeedsGot(uint32_t Type) const override;
   bool relocNeedsPlt(uint32_t Type) const override;
   void relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                    uint64_t BaseAddr, uint64_t SymVA) const override;
 };
 
+class MipsTargetInfo final : public TargetInfo {
+public:
+  MipsTargetInfo();
+  void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
+                     uint64_t PltEntryAddr) const override;
+  bool relocNeedsGot(uint32_t Type) const override;
+  bool relocNeedsPlt(uint32_t Type) const override;
+  void relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
+                   uint64_t BaseAddr, uint64_t SymVA) const override;
+};
+
 extern std::unique_ptr<TargetInfo> Target;
 }
 }
 
 #endif

lld/trunk/ELF/Target.cpp

void AArch64TargetInfo::relocateOne(uint8_t *Buf, const void *RelP,
   case R_AARCH64_ADR_PREL_LO21:
     handle_ADR_PREL_LO21(Location, S, A, P);
     break;
   default:
     error(Twine("unrecognized reloc ") + Twine(Type));
     break;
   }
 }
+
+MipsTargetInfo::MipsTargetInfo() {
+  // PCRelReloc = FIXME
+  // GotReloc = FIXME
+  DefaultEntry = "__start";
+}
+
+void MipsTargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
+                                   uint64_t PltEntryAddr) const {}
+
+bool MipsTargetInfo::relocNeedsGot(uint32_t Type) const { return false; }
+
+bool MipsTargetInfo::relocNeedsPlt(uint32_t Type) const { return false; }
+
+void MipsTargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
+                                 uint64_t BaseAddr, uint64_t SymVA) const {}
 }
 }

lld/trunk/test/elf2/basic-mips.s

+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux %s -o %t.o
+# RUN: lld -flavor gnu2 %t.o -o %t.exe
+# RUN: llvm-readobj -file-headers -sections -program-headers -symbols %t.exe \
+# RUN:   | FileCheck %s
+
+# REQUIRES: mips
+
+# Exits with return code 1 on Linux.
+        .globl  __start
+__start:
+        li      $a0,1
+        li      $v0,4001
+        syscall
+
+# CHECK:      ElfHeader {
+# CHECK-NEXT:   Ident {
+# CHECK-NEXT:     Magic: (7F 45 4C 46)
+# CHECK-NEXT:     Class: 32-bit (0x1)
+# CHECK-NEXT:     DataEncoding: LittleEndian (0x1)
+# CHECK-NEXT:     FileVersion: 1
+# CHECK-NEXT:     OS/ABI: SystemV (0x0)
+# CHECK-NEXT:     ABIVersion: 0
+# CHECK-NEXT:     Unused: (00 00 00 00 00 00 00)
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Type: Executable (0x2)
+# CHECK-NEXT:   Machine: EM_MIPS (0x8)
+# CHECK-NEXT:   Version: 1
+# CHECK-NEXT:   Entry: 0x11000
+# CHECK-NEXT:   ProgramHeaderOffset: 0x34
+# CHECK-NEXT:   SectionHeaderOffset: 0x2094
+# CHECK-NEXT:   Flags [ (0x0)
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   HeaderSize: 52
+# CHECK-NEXT:   ProgramHeaderEntrySize: 32
+# CHECK-NEXT:   ProgramHeaderCount: 3
+# CHECK-NEXT:   SectionHeaderEntrySize: 40
+# CHECK-NEXT:   SectionHeaderCount: 8
+# CHECK-NEXT:   StringTableSectionIndex: 7
+# CHECK-NEXT: }
+# CHECK-NEXT: Sections [
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 0
+# CHECK-NEXT:     Name:  (0)
+# CHECK-NEXT:     Type: SHT_NULL (0x0)
+# CHECK-NEXT:     Flags [ (0x0)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x0
+# CHECK-NEXT:     Offset: 0x0
+# CHECK-NEXT:     Size: 0
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 0
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 1
+# CHECK-NEXT:     Name: .bss (15)
+# CHECK-NEXT:     Type: SHT_NOBITS (0x8)
+# CHECK-NEXT:     Flags [ (0x3)
+# CHECK-NEXT:       SHF_ALLOC (0x2)
+# CHECK-NEXT:       SHF_WRITE (0x1)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x11000
+# CHECK-NEXT:     Offset: 0x1000
+# CHECK-NEXT:     Size: 0
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 16
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 2
+# CHECK-NEXT:     Name: .text (1)
+# CHECK-NEXT:     Type: SHT_PROGBITS (0x1)
+# CHECK-NEXT:     Flags [ (0x6)
+# CHECK-NEXT:       SHF_ALLOC (0x2)
+# CHECK-NEXT:       SHF_EXECINSTR (0x4)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x11000
+# CHECK-NEXT:     Offset: 0x1000
+# CHECK-NEXT:     Size: 12
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 16
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 3
+# CHECK-NEXT:     Name: .data (60)
+# CHECK-NEXT:     Type: SHT_PROGBITS (0x1)
+# CHECK-NEXT:     Flags [ (0x3)
+# CHECK-NEXT:       SHF_ALLOC (0x2)
+# CHECK-NEXT:       SHF_WRITE (0x1)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x11010
+# CHECK-NEXT:     Offset: 0x1010
+# CHECK-NEXT:     Size: 0
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 16
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 4
+# CHECK-NEXT:     Name: .reginfo (35)
+# CHECK-NEXT:     Type: SHT_MIPS_REGINFO (0x70000006)
+# CHECK-NEXT:     Flags [ (0x2)
+# CHECK-NEXT:       SHF_ALLOC (0x2)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x12000
+# CHECK-NEXT:     Offset: 0x2000
+# CHECK-NEXT:     Size: 24
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 4
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 5
+# CHECK-NEXT:     Name: .MIPS.abiflags (20)
+# CHECK-NEXT:     Type: SHT_MIPS_ABIFLAGS (0x7000002A)
+# CHECK-NEXT:     Flags [ (0x2)
+# CHECK-NEXT:       SHF_ALLOC (0x2)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x12018
+# CHECK-NEXT:     Offset: 0x2018
+# CHECK-NEXT:     Size: 24
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 8
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 6
+# CHECK-NEXT:     Name: .symtab (52)
+# CHECK-NEXT:     Type: SHT_SYMTAB (0x2)
+# CHECK-NEXT:     Flags [ (0x0)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x0
+# CHECK-NEXT:     Offset: 0x2030
+# CHECK-NEXT:     Size: 32
+# CHECK-NEXT:     Link: 7
+# CHECK-NEXT:     Info: 1
+# CHECK-NEXT:     AddressAlignment: 4
+# CHECK-NEXT:     EntrySize: 16
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 7
+# CHECK-NEXT:     Name: .strtab (44)
+# CHECK-NEXT:     Type: SHT_STRTAB (0x3)
+# CHECK-NEXT:     Flags [ (0x0)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x0
+# CHECK-NEXT:     Offset: 0x2050
+# CHECK-NEXT:     Size: 66
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 1
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+# CHECK-NEXT: Symbols [
+# CHECK-NEXT:   Symbol {
+# CHECK-NEXT:     Name:  (0)
+# CHECK-NEXT:     Value: 0x0
+# CHECK-NEXT:     Size: 0
+# CHECK-NEXT:     Binding: Local (0x0)
+# CHECK-NEXT:     Type: None (0x0)
+# CHECK-NEXT:     Other: 0
+# CHECK-NEXT:     Section: Undefined (0x0)
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Symbol {
+# CHECK-NEXT:     Name: __start (7)
+# CHECK-NEXT:     Value: 0x11000
+# CHECK-NEXT:     Size: 0
+# CHECK-NEXT:     Binding: Global (0x1)
+# CHECK-NEXT:     Type: None (0x0)
+# CHECK-NEXT:     Other: 0
+# CHECK-NEXT:     Section: .text (0x2)
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+# CHECK-NEXT: ProgramHeaders [
+# CHECK-NEXT:   ProgramHeader {
+# CHECK-NEXT:     Type: PT_LOAD (0x1)
+# CHECK-NEXT:     Offset: 0x0
+# CHECK-NEXT:     VirtualAddress: 0x10000
+# CHECK-NEXT:     PhysicalAddress: 0x10000
+# CHECK-NEXT:     FileSize: 148
+# CHECK-NEXT:     MemSize: 148
+# CHECK-NEXT:     Flags [ (0x4)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 4096
+# CHECK-NEXT:   }
+# CHECK-NEXT:   ProgramHeader {
+# CHECK-NEXT:     Type: PT_LOAD (0x1)
+# CHECK-NEXT:     Offset: 0x1000
+# CHECK-NEXT:     VirtualAddress: 0x11000
+# CHECK-NEXT:     PhysicalAddress: 0x11000
+# CHECK-NEXT:     FileSize: 16
+# CHECK-NEXT:     MemSize: 16
+# CHECK-NEXT:     Flags [ (0x5)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:       PF_X (0x1)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 4096
+# CHECK-NEXT:   }
+# CHECK-NEXT:   ProgramHeader {
+# CHECK-NEXT:     Type: PT_LOAD (0x1)
+# CHECK-NEXT:     Offset: 0x2000
+# CHECK-NEXT:     VirtualAddress: 0x12000
+# CHECK-NEXT:     PhysicalAddress: 0x12000
+# CHECK-NEXT:     FileSize: 48
+# CHECK-NEXT:     MemSize: 48
+# CHECK-NEXT:     Flags [ (0x4)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 4096
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]