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

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

Differential Revision: http://reviews.llvm.org/D17593

llvm-svn: 261879

lld/ELF/OutputSections.cpp

@@ -1509,6 +1509,14 @@ void SymbolTableSection<ELFT>::writeGlobalSymbols(uint8_t *Buf) {
       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;
   }
 }

lld/ELF/Target.cpp

@@ -228,6 +228,7 @@ public:
                    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
 
@@ -1705,8 +1706,12 @@ bool MipsTargetInfo<ELFT>::needsCopyRelImpl(uint32_t Type) const {
 
 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>
@@ -1716,8 +1721,6 @@ bool MipsTargetInfo<ELFT>::needsPltImpl(uint32_t Type,
     return false;
   if (Type == R_MIPS_26 && canBePreempted(&S, false))
     return true;
-  if (!isRelRelative(Type) && S.isShared())
-    return true;
   return false;
 }
 

lld/test/ELF/mips-sto-plt.s

@@ -0,0 +1,65 @@
+# 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