[PATCH] D16193: [ELF][MIPS] Ignore 'hint' relocations like R_MIPS_JALR in the `scanRelocs` method

[Simon Atanasyan via llvm-commits]

atanasyan created this revision.
atanasyan added reviewers: ruiu, rafael.
atanasyan added a subscriber: llvm-commits.
atanasyan set the repository for this revision to rL LLVM.
atanasyan added a project: lld.

MIPS ABI has relocations like R_MIPS_JALR which is just a hint for linker to make some code optimization. Such relocations should not be handled as a regular ones and lead to say dynamic relocation creation.

The patch introduces new virtual `Target::isHintReloc` method, overrides it in the `MipsTargetInfo` class and calls it in the `Writer<ELFT>::scanRelocs` method.

Repository:
  rL LLVM

http://reviews.llvm.org/D16193

Files:
  ELF/Target.cpp
  ELF/Target.h
  ELF/Writer.cpp
  test/ELF/mips-jalr.test

Index: test/ELF/mips-jalr.test
===================================================================
--- test/ELF/mips-jalr.test
+++ test/ELF/mips-jalr.test
@@ -3,11 +3,15 @@
 # RUN: yaml2obj -format elf %s -o %t.o
 # RUN: ld.lld %t.o -o %t.so -shared
 # RUN: llvm-objdump -d %t.so | FileCheck %s
+# RUN: llvm-readobj -relocations %t.so | FileCheck -check-prefix=REL %s
 
 # REQUIRES: mips
 
 # CHECK: 10000:   09 f8 20 03   jalr    $25
 
+# REL:      Relocations [
+# REL-NEXT: ]
+
 FileHeader:
   Class:    ELFCLASS32
   Data:     ELFDATA2LSB
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -212,6 +212,9 @@
     SymbolBody *Body = File.getSymbolBody(SymIndex);
     uint32_t Type = RI.getType(Config->Mips64EL);
 
+    if (Target->isHintReloc(Type))
+      continue;
+
     if (Target->isGotRelative(Type))
       HasGotOffRel = true;
 
Index: ELF/Target.h
===================================================================
--- ELF/Target.h
+++ ELF/Target.h
@@ -57,6 +57,11 @@
                              uint64_t GotEntryAddr, uint64_t PltEntryAddr,
                              int32_t Index, unsigned RelOff) const = 0;
 
+  // Returns true if a relocation is just a hint for linker to make for example
+  // some code optimization. Such relocations should not be handled as a regular
+  // ones and lead to dynamic relocation creation etc.
+  virtual bool isHintReloc(uint32_t Type) const;
+
   // Returns true if a relocation is relative to the place being relocated,
   // such as relocations used for PC-relative instructions. Such relocations
   // need not be fixed up if an image is loaded to a different address than
Index: ELF/Target.cpp
===================================================================
--- ELF/Target.cpp
+++ ELF/Target.cpp
@@ -239,6 +239,7 @@
   void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P,
                    uint64_t SA, uint64_t ZA = 0,
                    uint8_t *PairedLoc = nullptr) const override;
+  bool isHintReloc(uint32_t Type) const override;
   bool isRelRelative(uint32_t Type) const override;
 };
 } // anonymous namespace
@@ -284,6 +285,8 @@
 
 bool TargetInfo::isGotRelative(uint32_t Type) const { return false; }
 
+bool TargetInfo::isHintReloc(uint32_t Type) const { return false; }
+
 bool TargetInfo::isRelRelative(uint32_t Type) const { return true; }
 
 bool TargetInfo::isSizeReloc(uint32_t Type) const { return false; }
@@ -1581,6 +1584,11 @@
 }
 
 template <class ELFT>
+bool MipsTargetInfo<ELFT>::isHintReloc(uint32_t Type) const {
+  return Type == R_MIPS_JALR;
+}
+
+template <class ELFT>
 bool MipsTargetInfo<ELFT>::isRelRelative(uint32_t Type) const {
   switch (Type) {
   default:


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