[ELF][PPC32] Support range extension thunk with addends

[MaskRay]

Summary

• Generalize the code added in D70637 and D70937. We should eventually

remove EM_ARM and EM_MIPS special cases.

• Handle R_PPC_LOCAL24PC the same way as R_PPC_REL24.

[merge_guards_bot]

Unit tests: fail. 62196 tests passed, 1 failed and 815 were skipped.

failed: lld.ELF/ppc32-long-thunk.s

clang-tidy: fail. clang-tidy found 0 errors and 15 warnings. 0 of them are added as review comments below (why?).

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[MaskRay]

Handle R_PPC_LOCAL24PC as well

[merge_guards_bot]

Unit tests: pass. 62197 tests passed, 0 failed and 815 were skipped.

clang-tidy: fail. clang-tidy found 0 errors and 15 warnings. 0 of them are added as review comments below (why?).

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[MaskRay]

Simplify

[MaskRay]

Simplify

[merge_guards_bot]

Unit tests: pass. 62197 tests passed, 0 failed and 815 were skipped.

clang-tidy: fail. clang-tidy found 0 errors and 15 warnings. 0 of them are added as review comments below (why?).

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[merge_guards_bot]

Unit tests: pass. 62197 tests passed, 0 failed and 815 were skipped.

clang-tidy: fail. clang-tidy found 0 errors and 15 warnings. 0 of them are added as review comments below (why?).

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[MaskRay]

Simplify via getPCBias()

[merge_guards_bot]

Unit tests: pass. 62197 tests passed, 0 failed and 815 were skipped.

clang-tidy: fail. clang-tidy found 0 errors and 15 warnings. 0 of them are added as review comments below (why?).

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[Bdragon28]

This is necessary to run large programs like clang on FreeBSD powerpc32 when built with lld, because of REL24 branches in the crt startup code (done on purpose for object reusability reasons -- the csu objects need to work on both non-pic and pic, so they just use a plain bl and rely on the link editor to do a thunk if necessary.)

Looks good to me from a functionality standpoint on powerpc32.

lld/ELF/Arch/PPC.cpp

 }
 
 void PPC::writeGotPlt(uint8_t *buf, const Symbol &s) const {
   // Address of the symbol resolver stub in .glink .
   write32(buf, in.plt->getVA() + in.plt->headerSize + 4 * s.pltIndex);
 }
 
 bool PPC::needsThunk(RelExpr expr, RelType type, const InputFile *file,
-                     uint64_t branchAddr, const Symbol &s, int64_t /*a*/) const {
-  if (type != R_PPC_REL24 && type != R_PPC_PLTREL24)
+                     uint64_t branchAddr, const Symbol &s, int64_t a) const {
+  if (type != R_PPC_LOCAL24PC && type != R_PPC_REL24 && type != R_PPC_PLTREL24)
     return false;
   if (s.isInPlt())
     return true;
   if (s.isUndefWeak())
     return false;
-  return !(expr == R_PC && PPC::inBranchRange(type, branchAddr, s.getVA()));
+  return !PPC::inBranchRange(type, branchAddr, s.getVA(a));
 }
 
 uint32_t PPC::getThunkSectionSpacing() const { return 0x2000000; }
 
 bool PPC::inBranchRange(RelType type, uint64_t src, uint64_t dst) const {
   uint64_t offset = dst - src;
-  if (type == R_PPC_REL24 || type == R_PPC_PLTREL24)
+  if (type == R_PPC_LOCAL24PC || type == R_PPC_REL24 || type == R_PPC_PLTREL24)
     return isInt<26>(offset);
   llvm_unreachable("unsupported relocation type used in branch");
 }
 
 RelExpr PPC::getRelExpr(RelType type, const Symbol &s,
                         const uint8_t *loc) const {
   switch (type) {
   case R_PPC_NONE:
     return R_NONE;
   case R_PPC_ADDR16_HA:
   case R_PPC_ADDR16_HI:
   case R_PPC_ADDR16_LO:
   case R_PPC_ADDR32:
     return R_ABS;
   case R_PPC_DTPREL16:
   case R_PPC_DTPREL16_HA:
   case R_PPC_DTPREL16_HI:
   case R_PPC_DTPREL16_LO:
   case R_PPC_DTPREL32:
     return R_DTPREL;
   case R_PPC_REL14:
   case R_PPC_REL32:
-  case R_PPC_LOCAL24PC:
   case R_PPC_REL16_LO:
   case R_PPC_REL16_HI:
   case R_PPC_REL16_HA:
     return R_PC;
   case R_PPC_GOT16:
     return R_GOT_OFF;
+  case R_PPC_LOCAL24PC:
   case R_PPC_REL24:
     return R_PLT_PC;
   case R_PPC_PLTREL24:
     return R_PPC32_PLTREL;
   case R_PPC_GOT_TLSGD16:
     return R_TLSGD_GOT;
   case R_PPC_GOT_TLSLD16:
     return R_TLSLD_GOT;

lld/ELF/Relocations.cpp

static void scanReloc(InputSectionBase &sec, OffsetGetter &getOffset, RelTy *&i,
   // example, if we are linking a main executable, all dynamic symbols that can
   // be resolved within the executable will actually be resolved that way at
   // runtime, because the main executable is always at the beginning of a search
   // list. We can leverage that fact.
   if (!sym.isPreemptible && (!sym.isGnuIFunc() || config->zIfuncNoplt)) {
     if (expr == R_GOT_PC && !isAbsoluteValue(sym)) {
       expr = target->adjustRelaxExpr(type, relocatedAddr, expr);
     } else {
-      // Addend of R_PPC_PLTREL24 is used to choose call stub type. It should be
-      // ignored if optimized to R_PC.
+      // The 0x8000 bit of r_addend of R_PPC_PLTREL24 is used to choose call
+      // stub type. It should be ignored if optimized to R_PC.
       if (config->emachine == EM_PPC && expr == R_PPC32_PLTREL)
-        addend = 0;
+        addend &= ~0x8000;
       expr = fromPlt(expr);
     }
   }
 
   // If the relocation does not emit a GOT or GOTPLT entry but its computation
   // uses their addresses, we need GOT or GOTPLT to be created.
   //
   // The 4 types that relative GOTPLT are all x86 and x86-64 specific.

 // relocation back to its original non-Thunk target.
 bool ThunkCreator::normalizeExistingThunk(Relocation &rel, uint64_t src) {
   if (Thunk *t = thunks.lookup(rel.sym)) {
     if (target->inBranchRange(rel.type, src,
                               rel.sym->getVA(rel.addend) + getPCBias(rel.type)))
       return true;
     rel.sym = &t->destination;
     // TODO Restore addend on all targets.
-    if (config->emachine == EM_AARCH64 || config->emachine == EM_PPC64)
+    if (config->emachine != EM_ARM && config->emachine != EM_MIPS)
       rel.addend = t->addend;
     if (rel.sym->isInPlt())
       rel.expr = toPlt(rel.expr);
   }
   return false;
 }
 
 // Process all relocations from the InputSections that have been assigned
forEachInputSectionDescription(
               ts->addThunk(t);
               thunks[t->getThunkTargetSym()] = t;
             }
 
             // Redirect relocation to Thunk, we never go via the PLT to a Thunk
             rel.sym = t->getThunkTargetSym();
             rel.expr = fromPlt(rel.expr);
 
-            // On AArch64 and PPC64, a jump/call relocation may be encoded as
+            // On AArch64 and PPC, a jump/call relocation may be encoded as
             // STT_SECTION + non-zero addend, clear the addend after
             // redirection.
-            //
-            // The addend of R_PPC_PLTREL24 should be ignored after changing to
-            // R_PC.
-            if (config->emachine == EM_AARCH64 ||
-                config->emachine == EM_PPC64 ||
-                (config->emachine == EM_PPC && rel.type == R_PPC_PLTREL24))
+            if (config->emachine != EM_ARM && config->emachine != EM_MIPS)
               rel.addend = 0;
           }
 
         for (auto &p : isd->thunkSections)
           addressesChanged |= p.first->assignOffsets();
       });
 
   for (auto &p : thunkedSections)

lld/ELF/Thunks.cpp

 };
 
 class PPC32PltCallStub final : public Thunk {
 public:
   // For R_PPC_PLTREL24, Thunk::addend records the addend which will be used to
   // decide the offsets in the call stub.
   PPC32PltCallStub(const InputSection &isec, const Relocation &rel,
                    Symbol &dest)
-      : Thunk(dest, rel.type == R_PPC_PLTREL24 ? rel.addend : 0),
-        file(isec.file) {}
+      : Thunk(dest, rel.addend), file(isec.file) {}
   uint32_t size() override { return 16; }
   void writeTo(uint8_t *buf) override;
   void addSymbols(ThunkSection &isec) override;
   bool isCompatibleWith(const InputSection &isec, const Relocation &rel) const override;
 
 private:
   // Records the call site of the call stub.
   const InputFile *file;
 };
 
+class PPC32LongThunk final : public Thunk {
+public:
+  PPC32LongThunk(Symbol &dest, int64_t addend) : Thunk(dest, addend) {}
+  uint32_t size() override { return config->isPic ? 32 : 16; }
+  void writeTo(uint8_t *buf) override;
+  void addSymbols(ThunkSection &isec) override;
+};
+
 // PPC64 Plt call stubs.
 // Any call site that needs to call through a plt entry needs a call stub in
 // the .text section. The call stub is responsible for:
 // 1) Saving the toc-pointer to the stack.
 // 2) Loading the target functions address from the procedure linkage table into
 //    r12 for use by the target functions global entry point, and into the count
 //    register.
 // 3) Transferring control to the target function through an indirect branch.
void PPC32PltCallStub::addSymbols(ThunkSection &isec) {
   addSymbol(saver.save(os.str()), STT_FUNC, 0, isec);
 }
 
 bool PPC32PltCallStub::isCompatibleWith(const InputSection &isec,
                                         const Relocation &rel) const {
   return !config->isPic || (isec.file == file && rel.addend == addend);
 }
 
+void PPC32LongThunk::addSymbols(ThunkSection &isec) {
+  addSymbol(saver.save("__LongThunk_" + destination.getName()), STT_FUNC, 0,
+            isec);
+}
+
+void PPC32LongThunk::writeTo(uint8_t *buf) {
+  auto ha = [](uint32_t v) -> uint16_t { return (v + 0x8000) >> 16; };
+  auto lo = [](uint32_t v) -> uint16_t { return v; };
+  uint32_t d = destination.getVA(addend);
+  if (config->isPic) {
+    uint32_t off = d - (getThunkTargetSym()->getVA() + 8);
+    write32(buf + 0, 0x7c0802a6);            // mflr r12,0
+    write32(buf + 4, 0x429f0005);            // bcl r20,r31,.+4
+    write32(buf + 8, 0x7d8802a6);            // mtctr r12
+    write32(buf + 12, 0x3d8c0000 | ha(off)); // addis r12,r12,off@ha
+    write32(buf + 16, 0x398c0000 | lo(off)); // addi r12,r12,off@l
+    write32(buf + 20, 0x7c0803a6);           // mtlr r0
+    buf += 24;
+  } else {
+    write32(buf + 0, 0x3d800000 | ha(d));    // lis r12,d@ha
+    write32(buf + 4, 0x398c0000 | lo(d));    // addi r12,r12,d@l
+    buf += 8;
+  }
+  write32(buf + 0, 0x7d8903a6);              // mtctr r12
+  write32(buf + 4, 0x4e800420);              // bctr
+}
+
 void writePPC64LoadAndBranch(uint8_t *buf, int64_t offset) {
   uint16_t offHa = (offset + 0x8000) >> 16;
   uint16_t offLo = offset & 0xffff;
 
   write32(buf + 0, 0x3d820000 | offHa); // addis r12, r2, OffHa
   write32(buf + 4, 0xe98c0000 | offLo); // ld    r12, OffLo(r12)
   write32(buf + 8, 0x7d8903a6);         // mtctr r12
   write32(buf + 12, 0x4e800420);        // bctr
if ((s.stOther & STO_MIPS_MICROMIPS) && isMipsR6())
     return make<MicroMipsR6Thunk>(s);
   if (s.stOther & STO_MIPS_MICROMIPS)
     return make<MicroMipsThunk>(s);
   return make<MipsThunk>(s);
 }
 
 static Thunk *addThunkPPC32(const InputSection &isec, const Relocation &rel,
                             Symbol &s) {
-  assert((rel.type == R_PPC_REL24 || rel.type == R_PPC_PLTREL24) &&
+  assert((rel.type == R_PPC_LOCAL24PC || rel.type == R_PPC_REL24 ||
+          rel.type == R_PPC_PLTREL24) &&
          "unexpected relocation type for thunk");
+  if (s.isInPlt())
     return make<PPC32PltCallStub>(isec, rel, s);
+  return make<PPC32LongThunk>(s, rel.addend);
 }
 
 static Thunk *addThunkPPC64(RelType type, Symbol &s, int64_t a) {
   assert(type == R_PPC64_REL24 && "unexpected relocation type for thunk");
   if (s.isInPlt())
     return make<PPC64PltCallStub>(s);
 
   if (config->picThunk)

lld/test/ELF/ppc32-long-thunk.s

+# REQUIRES: ppc
+# RUN: echo 'SECTIONS { \
+# RUN:       .text_low 0x2000: { *(.text_low) } \
+# RUN:       .text_high 0x2002000 : { *(.text_high) } \
+# RUN:       }' > %t.script
+
+# RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
+# RUN: ld.lld -T %t.script %t.o -o %t
+# RUN: llvm-readelf -r %t | FileCheck --check-prefix=SEC %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefixes=CHECK,PD %s
+
+# RUN: ld.lld -T %t.script -pie %t.o -o %t
+# RUN: llvm-readelf -r %t | FileCheck --check-prefix=SEC %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefixes=CHECK,PI %s
+
+# SEC: There are no relocations in this file.
+
+# CHECK:      _start:
+# CHECK-NEXT:     2000: bl .+24
+# CHECK-NEXT:           bl .+20
+# CHECK-NEXT:           bl .+16
+# CHECK-NEXT:           bl .+33554428
+# PD-NEXT:              bl .+24
+# PI-NEXT:              bl .+40
+
+## high = 0x02002008 = 65536*512+8200
+# PD:         __LongThunk_high:
+# PD-NEXT:        2018: lis 12, 512
+# PD-NEXT:              addi 12, 12, 8200
+# PD-NEXT:              mtctr 12
+# PD-NEXT:              bctr
+
+## .text_high+16 = 0x02002010 = 65536*512+8208
+# PD:         __LongThunk_:
+# PD-NEXT:        2028: lis 12, 512
+# PD-NEXT:              addi 12, 12, 8208
+# PD-NEXT:              mtctr 12
+# PD-NEXT:              bctr
+
+## high-0x2028 = 0x02002008-0x2020 = 65536*512-24
+# PI:         __LongThunk_high:
+# PI-NEXT:        2018: mflr 0
+# PI-NEXT:              bcl 20, 31, .+4
+# PI-NEXT:        2020: mflr 12
+# PI-NEXT:              addis 12, 12, 512
+# PI-NEXT:              addi 12, 12, -24
+# PI-NEXT:              mtlr 0
+# PI-NEXT:              mtctr 12
+# PI-NEXT:              bctr
+
+## .text_high+16-0x2048 = 0x02002010-0x2048 = 65536*512-48
+# PI:         __LongThunk_:
+# PI-NEXT:        2038: mflr 0
+# PI-NEXT:              bcl 20, 31, .+4
+# PI-NEXT:        2040: mflr 12
+# PI-NEXT:              addis 12, 12, 512
+# PI-NEXT:              addi 12, 12, -48
+# PI-NEXT:              mtlr 0
+# PI-NEXT:              mtctr 12
+# PI-NEXT:              bctr
+
+.section .text_low, "ax", %progbits
+.globl _start
+_start:
+bl high@local     # Need a thunk
+bl high@local     # Need a thunk
+bl high+32768@plt # Need a thunk
+bl high
+bl .text_high+16 # Need a thunk
+blr
+
+# PD:         02002008 high:
+# PD-NEXT:             bl .-33554432
+# PD-NEXT:             bl .+4
+# PD:         __LongThunk_:
+# PD-NEXT:    2002010: lis 12, 0
+# PD-NEXT:             addi 12, 12, 8200
+# PD-NEXT:             mtctr 12
+# PD-NEXT:             bctr
+
+.section .text_high, "ax", %progbits
+nop
+nop
+.globl high
+high:
+bl .text_low+8
+bl .text_low+8    # Need a thunk