[ELF][MIPS] Add STO_MIPS_PLT flag to the symbols require pointer equality

[atanasyan]

Summary

On MIPS we need to mark symbol which has a PLT entry and requires pointer equality by STO_MIPS_PLT flag. That is necessary to help dynamic linker distinguish such symbols and MIPS lazy-binding stubs.

https://sourceware.org/ml/binutils/2008-07/txt00000.txt

[• rafael]

LGTM, but please consider updating llvm-readobj to print STO_MIPS_PLT instead of 8.

[ruiu]

LGTM

lld/trunk/ELF/OutputSections.cpp

1519 ↗

(On Diff #49068)

I think you can remove "ELF::"

ELF/OutputSections.cpp

for (const std::pair<SymbolBody *, size_t> &P : Symbols) {
     ESym->st_name = StrOff;
     ESym->setVisibility(Body->getVisibility());
     ESym->st_value = Body->getVA<ELFT>();
 
     if (const OutputSectionBase<ELFT> *OutSec = getOutputSection(Body))
       ESym->st_shndx = OutSec->SectionIndex;
     else if (isa<DefinedRegular<ELFT>>(Body))
       ESym->st_shndx = SHN_ABS;
+
+    // On MIPS we need to mark symbol which has a PLT entry and requires pointer
+    // equality by STO_MIPS_PLT flag. That is necessary to help dynamic linker
+    // distinguish such symbols and MIPS lazy-binding stubs.
+    // https://sourceware.org/ml/binutils/2008-07/txt00000.txt
+    if (Config->EMachine == EM_MIPS && Body->isInPlt() &&
+        Body->NeedsCopyOrPltAddr)
+      ESym->st_other |= ELF::STO_MIPS_PLT;
     ++ESym;
   }
 }
 
 template <class ELFT>
 const OutputSectionBase<ELFT> *
 SymbolTableSection<ELFT>::getOutputSection(SymbolBody *Sym) {
   switch (Sym->kind()) {

ELF/Target.cpp

public:
   bool needsCopyRelImpl(uint32_t Type) const override;
   bool needsGot(uint32_t Type, SymbolBody &S) const override;
   bool needsPltImpl(uint32_t Type, const SymbolBody &S) const override;
   void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P,
                    uint64_t S, uint64_t ZA = 0,
                    uint8_t *PairedLoc = nullptr) const override;
   bool isHintRel(uint32_t Type) const override;
   bool isRelRelative(uint32_t Type) const override;
+  bool refersToGotEntry(uint32_t Type) const override;
 };
 } // anonymous namespace
 
 TargetInfo *createTarget() {
   switch (Config->EMachine) {
   case EM_386:
     return new X86TargetInfo();
   case EM_AARCH64:

 
 template <class ELFT>
 bool MipsTargetInfo<ELFT>::needsCopyRelImpl(uint32_t Type) const {
   return !isRelRelative(Type);
 }
 
 template <class ELFT>
 bool MipsTargetInfo<ELFT>::needsGot(uint32_t Type, SymbolBody &S) const {
-  return needsPlt<ELFT>(Type, S) || Type == R_MIPS_GOT16 ||
-         Type == R_MIPS_CALL16;
+  return needsPlt<ELFT>(Type, S) || refersToGotEntry(Type);
+}
+
+template <class ELFT>
+bool MipsTargetInfo<ELFT>::refersToGotEntry(uint32_t Type) const {
+  return Type == R_MIPS_GOT16 || Type == R_MIPS_CALL16;
 }
 
 template <class ELFT>
 bool MipsTargetInfo<ELFT>::needsPltImpl(uint32_t Type,
                                         const SymbolBody &S) const {
   if (needsCopyRel<ELFT>(Type, S))
     return false;
   if (Type == R_MIPS_26 && canBePreempted(&S, false))
     return true;
-  if (!isRelRelative(Type) && S.isShared())
-    return true;
   return false;
 }
 
 template <class ELFT>
 void MipsTargetInfo<ELFT>::relocateOne(uint8_t *Loc, uint8_t *BufEnd,
                                        uint32_t Type, uint64_t P, uint64_t S,
                                        uint64_t ZA, uint8_t *PairedLoc) const {
   const endianness E = ELFT::TargetEndianness;

test/ELF/mips-sto-plt.s

+# Check assigning STO_MIPS_PLT flag to symbol needs a pointer equality.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         %S/Inputs/mips-dynamic.s -o %t.so.o
+# RUN: ld.lld %t.so.o -shared -o %t.so
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o %t.so -o %t.exe
+# RUN: llvm-readobj -dt -mips-plt-got %t.exe | FileCheck %s
+
+# REQUIRES: mips
+
+# CHECK:      Symbol {
+# CHECK:        Name: foo0@
+# CHECK-NEXT:   Value: 0x0
+# CHECK-NEXT:   Size: 0
+# CHECK-NEXT:   Binding: Global
+# CHECK-NEXT:   Type: Function
+# CHECK-NEXT:   Other: 0
+# CHECK-NEXT:   Section: Undefined
+# CHECK-NEXT: }
+# CHECK:      Symbol {
+# CHECK:        Name: foo1@
+# CHECK-NEXT:   Value: 0x20050
+# CHECK-NEXT:   Size: 0
+# CHECK-NEXT:   Binding: Global
+# CHECK-NEXT:   Type: Function
+# CHECK-NEXT:   Other: 8
+#                      ^-- STO_MIPS_PLT
+# CHECK-NEXT:   Section: Undefined
+# CHECK-NEXT: }
+
+# CHECK:      Primary GOT {
+# CHECK:        Local entries [
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Global entries [
+# CHECK-NEXT:   ]
+# CHECK:      PLT GOT {
+# CHECK:        Entries [
+# CHECK-NEXT:     Entry {
+# CHECK-NEXT:       Address:
+# CHECK-NEXT:       Initial:
+# CHECK-NEXT:       Value: 0x0
+# CHECK-NEXT:       Type: Function
+# CHECK-NEXT:       Section: Undefined
+# CHECK-NEXT:       Name: foo0
+# CHECK-NEXT:     }
+# CHECK-NEXT:     Entry {
+# CHECK-NEXT:       Address:
+# CHECK-NEXT:       Initial:
+# CHECK-NEXT:       Value: 0x20050
+# CHECK-NEXT:       Type: Function
+# CHECK-NEXT:       Section: Undefined
+# CHECK-NEXT:       Name: foo1
+# CHECK-NEXT:     }
+# CHECK-NEXT:   ]
+
+  .text
+  .globl __start
+__start:
+  jal    foo0               # R_MIPS_26 against 'foo0' from DSO
+  lui    $t0,%hi(foo1)      # R_MIPS_HI16/LO16 against 'foo1' from DSO
+  addi   $t0,$t0,%lo(foo1)
+
+loc:
+  nop