[ELF] Introduce Thunk reuse compatibility

smithp35 · smithp35 · commit 7d66e849fc70 · 2017-07-05T09:36:03.000Z
On ARM the interworking thunks are only produced for branch instructions that can't be changed into a blx instruction so only Thumb callers would call Thumb thunks and only ARM callers would call ARM thunks. With range extension thunks branch and link instructions may need a Thunk. These instructions can be rewritten as a blx and can use either ARM or Thumb thunks. We introduce an isCompatibleWith() function so that a caller can check if an existing Thunk is compatible before reusing it. Differential Revision: https://reviews.llvm.org/D34035 llvm-svn: 307132
diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
@@ -1050,7 +1050,7 @@ ThunkSection *ThunkCreator::addThunkSection(OutputSection *OS,
 std::pair<Thunk *, bool> ThunkCreator::getThunk(SymbolBody &Body,
                                                 uint32_t Type) {
   auto res = ThunkedSymbols.insert({&Body, nullptr});
-  if (res.second)
+  if (res.second || !res.first->second->isCompatibleWith(Type))
     res.first->second = addThunk(Type, Body);
   return std::make_pair(res.first->second, res.second);
 }
diff --git a/lld/ELF/Thunks.cpp b/lld/ELF/Thunks.cpp
@@ -57,6 +57,7 @@ class ARMV7ABSLongThunk final : public Thunk {
   uint32_t size() const override { return 12; }
   void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
   void addSymbols(ThunkSection &IS) override;
+  bool isCompatibleWith(uint32_t RelocType) const override;
 };
 
 class ARMV7PILongThunk final : public Thunk {
@@ -66,6 +67,7 @@ class ARMV7PILongThunk final : public Thunk {
   uint32_t size() const override { return 16; }
   void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
   void addSymbols(ThunkSection &IS) override;
+  bool isCompatibleWith(uint32_t RelocType) const override;
 };
 
 class ThumbV7ABSLongThunk final : public Thunk {
@@ -77,6 +79,7 @@ class ThumbV7ABSLongThunk final : public Thunk {
   uint32_t size() const override { return 10; }
   void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
   void addSymbols(ThunkSection &IS) override;
+  bool isCompatibleWith(uint32_t RelocType) const override;
 };
 
 class ThumbV7PILongThunk final : public Thunk {
@@ -88,6 +91,7 @@ class ThumbV7PILongThunk final : public Thunk {
   uint32_t size() const override { return 12; }
   void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
   void addSymbols(ThunkSection &IS) override;
+  bool isCompatibleWith(uint32_t RelocType) const override;
 };
 
 // MIPS LA25 thunk
@@ -128,6 +132,11 @@ void ARMV7ABSLongThunk::addSymbols(ThunkSection &IS) {
   addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, &IS);
 }
 
+bool ARMV7ABSLongThunk::isCompatibleWith(uint32_t RelocType) const {
+  // Thumb branch relocations can't use BLX
+  return RelocType != R_ARM_THM_JUMP19 && RelocType != R_ARM_THM_JUMP24;
+}
+
 void ThumbV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
   const uint8_t Data[] = {
       0x40, 0xf2, 0x00, 0x0c, // movw         ip, :lower16:S
@@ -147,6 +156,12 @@ void ThumbV7ABSLongThunk::addSymbols(ThunkSection &IS) {
   addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS);
 }
 
+bool ThumbV7ABSLongThunk::isCompatibleWith(uint32_t RelocType) const {
+  // ARM branch relocations can't use BLX
+  return RelocType != R_ARM_JUMP24 && RelocType != R_ARM_PC24 &&
+         RelocType != R_ARM_PLT32;
+}
+
 void ARMV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
   const uint8_t Data[] = {
       0xf0, 0xcf, 0x0f, 0xe3, // P:  movw ip,:lower16:S - (P + (L1-P) +8)
@@ -168,6 +183,11 @@ void ARMV7PILongThunk::addSymbols(ThunkSection &IS) {
   addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, &IS);
 }
 
+bool ARMV7PILongThunk::isCompatibleWith(uint32_t RelocType) const {
+  // Thumb branch relocations can't use BLX
+  return RelocType != R_ARM_THM_JUMP19 && RelocType != R_ARM_THM_JUMP24;
+}
+
 void ThumbV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
   const uint8_t Data[] = {
       0x4f, 0xf6, 0xf4, 0x7c, // P:  movw ip,:lower16:S - (P + (L1-P) + 4)
@@ -189,6 +209,12 @@ void ThumbV7PILongThunk::addSymbols(ThunkSection &IS) {
   addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS);
 }
 
+bool ThumbV7PILongThunk::isCompatibleWith(uint32_t RelocType) const {
+  // ARM branch relocations can't use BLX
+  return RelocType != R_ARM_JUMP24 && RelocType != R_ARM_PC24 &&
+         RelocType != R_ARM_PLT32;
+}
+
 // Write MIPS LA25 thunk code to call PIC function from the non-PIC one.
 void MipsThunk::writeTo(uint8_t *Buf, ThunkSection &) const {
   uint64_t S = Destination.getVA();
diff --git a/lld/ELF/Thunks.h b/lld/ELF/Thunks.h
@@ -41,6 +41,10 @@ class Thunk {
   // a branch and fall through to the first Symbol in the Target.
   virtual InputSection *getTargetInputSection() const { return nullptr; }
 
+  // To reuse a Thunk the caller as identified by the RelocType must be
+  // compatible with it.
+  virtual bool isCompatibleWith(uint32_t RelocType) const { return true; }
+
   // The alignment requirement for this Thunk, defaults to the size of the
   // typical code section alignment.
   const SymbolBody &Destination;

Original file line number	Diff line number	Diff line change
`@@ -1050,7 +1050,7 @@ ThunkSection ThunkCreator::addThunkSection(OutputSection OS,`
`1050`	`1050`	`std::pair<Thunk *, bool> ThunkCreator::getThunk(SymbolBody &Body,`
`1051`	`1051`	`uint32_t Type) {`
`1052`	`1052`	`auto res = ThunkedSymbols.insert({&Body, nullptr});`
`1053`		`- if (res.second)`
	`1053`	`+ if (res.second \|\| !res.first->second->isCompatibleWith(Type))`
`1054`	`1054`	`res.first->second = addThunk(Type, Body);`
`1055`	`1055`	`return std::make_pair(res.first->second, res.second);`
`1056`	`1056`	`}`