[LLD][PowerPC] Add a pc-rel based long branch thunk

In this patch, a pc-rel based long branch thunk is added for the local
call protocol that caller and callee does not use TOC.

Reviewed By: sfertile, nemanjai

Differential Revision: https://reviews.llvm.org/D86706

lld/ELF/Thunks.cpp

@@ -326,7 +326,7 @@ public:
 
 // A bl instruction uses a signed 24 bit offset, with an implicit 4 byte
 // alignment. This gives a possible 26 bits of 'reach'. If the call offset is
-// larger then that we need to emit a long-branch thunk. The target address
+// larger than that we need to emit a long-branch thunk. The target address
 // of the callee is stored in a table to be accessed TOC-relative. Since the
 // call must be local (a non-local call will have a PltCallStub instead) the
 // table stores the address of the callee's local entry point. For
@@ -337,6 +337,8 @@ public:
   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;
 
 protected:
   PPC64LongBranchThunk(Symbol &dest, int64_t addend) : Thunk(dest, addend) {}
@@ -365,6 +367,24 @@ public:
   }
 };
 
+// A bl instruction uses a signed 24 bit offset, with an implicit 4 byte
+// alignment. This gives a possible 26 bits of 'reach'. If the caller and
+// callee do not use toc and the call offset is larger than 26 bits,
+// we need to emit a pc-rel based long-branch thunk. The target address of
+// the callee is computed with a PC-relative offset.
+class PPC64PCRelLongBranchThunk final : public Thunk {
+public:
+  PPC64PCRelLongBranchThunk(Symbol &dest, int64_t addend)
+      : Thunk(dest, addend) {
+    alignment = 16;
+  }
+  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;
+};
+
 } // end anonymous namespace
 
 Defined *Thunk::addSymbol(StringRef name, uint8_t type, uint64_t value,
@@ -937,6 +957,33 @@ void PPC64LongBranchThunk::addSymbols(ThunkSection &isec) {
             isec);
 }
 
+bool PPC64LongBranchThunk::isCompatibleWith(const InputSection &isec,
+                                            const Relocation &rel) const {
+  return rel.type == R_PPC64_REL24 || rel.type == R_PPC64_REL14;
+}
+
+void PPC64PCRelLongBranchThunk::writeTo(uint8_t *buf) {
+  int64_t offset = destination.getVA() - getThunkTargetSym()->getVA();
+  if (!isInt<34>(offset))
+    fatal("offset overflow 34 bits, please compile using the large code model");
+  uint64_t paddi = PADDI_R12_NO_DISP | (((offset >> 16) & 0x3ffff) << 32) |
+                   (offset & 0xffff);
+
+  writePrefixedInstruction(buf + 0, paddi); // paddi r12, 0, func@pcrel, 1
+  write32(buf + 8, MTCTR_R12);              // mtctr r12
+  write32(buf + 12, BCTR);                  // bctr
+}
+
+void PPC64PCRelLongBranchThunk::addSymbols(ThunkSection &isec) {
+  addSymbol(saver.save("__long_branch_pcrel_" + destination.getName()),
+            STT_FUNC, 0, isec);
+}
+
+bool PPC64PCRelLongBranchThunk::isCompatibleWith(const InputSection &isec,
+                                                 const Relocation &rel) const {
+  return rel.type == R_PPC64_REL24_NOTOC;
+}
+
 Thunk::Thunk(Symbol &d, int64_t a) : destination(d), addend(a), offset(0) {}
 
 Thunk::~Thunk() = default;
@@ -1057,12 +1104,15 @@ static Thunk *addThunkPPC64(RelType type, Symbol &s, int64_t a) {
                                        : (Thunk *)make<PPC64PltCallStub>(s);
 
   // This check looks at the st_other bits of the callee. If the value is 1
-  // then the callee clobbers the TOC and we need an R2 save stub.
-  if ((s.stOther >> 5) == 1)
+  // then the callee clobbers the TOC and we need an R2 save stub when RelType
+  // is R_PPC64_REL14 or R_PPC64_REL24.
+  if ((type == R_PPC64_REL14 || type == R_PPC64_REL24) && (s.stOther >> 5) == 1)
     return make<PPC64R2SaveStub>(s);
 
-  if (type == R_PPC64_REL24_NOTOC && (s.stOther >> 5) > 1)
-    return make<PPC64R12SetupStub>(s);
+  if (type == R_PPC64_REL24_NOTOC)
+    return (s.stOther >> 5) > 1
+               ? (Thunk *)make<PPC64R12SetupStub>(s)
+               : (Thunk *)make<PPC64PCRelLongBranchThunk>(s, a);
 
   if (config->picThunk)
     return make<PPC64PILongBranchThunk>(s, a);

lld/test/ELF/ppc64-pcrel-long-branch-error.s

@@ -0,0 +1,31 @@
+# REQUIRES: ppc
+# RUN: echo 'SECTIONS { \
+# RUN:       .text_low 0x2000: { *(.text_low) } \
+# RUN:       .text_high 0x800002000 : { *(.text_high) } \
+# RUN:       }' > %t.script
+
+# RUN: llvm-mc -filetype=obj -triple=ppc64le %s -o %t.o
+# RUN: not ld.lld -T %t.script %t.o -o %t 2>&1 >/dev/null | FileCheck %s
+# RUN: llvm-mc -filetype=obj -triple=ppc64le -defsym HIDDEN=1 %s -o %t.o
+# RUN: not ld.lld -shared -T %t.script %t.o -o %t.so 2>&1 >/dev/null | FileCheck %s
+
+# RUN: llvm-mc -filetype=obj -triple=ppc64 %s -o %t.o
+# RUN: not ld.lld -T %t.script %t.o -o %t 2>&1 >/dev/null | FileCheck %s
+# RUN: llvm-mc -filetype=obj -triple=ppc64 -defsym HIDDEN=1 %s -o %t.o
+# RUN: not ld.lld -shared -T %t.script %t.o -o %t.so 2>&1 >/dev/null | FileCheck %s
+
+# CHECK: error: offset overflow 34 bits, please compile using the large code model
+
+.section .text_low, "ax", %progbits
+.globl _start
+_start:
+  bl high@notoc
+  blr
+
+.section .text_high, "ax", %progbits
+.ifdef HIDDEN
+.hidden high
+.endif
+.globl high
+high:
+  blr

lld/test/ELF/ppc64-pcrel-long-branch.s

@@ -0,0 +1,50 @@
+# 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=ppc64le %s -o %t.o
+# RUN: ld.lld -T %t.script %t.o -o %t
+# RUN: llvm-objdump -d --no-show-raw-insn --mcpu=pwr10 %t | FileCheck %s
+
+# RUN: llvm-mc -filetype=obj -triple=ppc64le -defsym HIDDEN=1 %s -o %t.o
+# RUN: ld.lld -shared -T %t.script %t.o -o %t.so
+# RUN: llvm-objdump -d --no-show-raw-insn --mcpu=pwr10 %t.so | FileCheck %s
+
+# RUN: llvm-mc -filetype=obj -triple=ppc64 %s -o %t.o
+# RUN: ld.lld -T %t.script %t.o -o %t
+# RUN: llvm-objdump -d --no-show-raw-insn --mcpu=pwr10 %t | FileCheck %s
+
+# RUN: llvm-mc -filetype=obj -triple=ppc64 -defsym HIDDEN=1 %s -o %t.o
+# RUN: ld.lld -shared -T %t.script %t.o -o %t.so
+# RUN: llvm-objdump -d --no-show-raw-insn --mcpu=pwr10 %t.so | FileCheck %s
+
+# CHECK-LABEL: <_start>:
+# CHECK-NEXT:    2000: bl 0x2010
+# CHECK-NEXT:          blr
+# CHECK-NEXT:          trap
+# CHECK-NEXT:          trap
+
+## Callee address - program counter = 0x2002000 - 0x2010 = 33554416
+# CHECK-LABEL: <__long_branch_pcrel_high>:
+# CHECK-NEXT:    2010: paddi 12, 0, 33554416, 1
+# CHECK-NEXT:          mtctr 12
+# CHECK-NEXT:          bctr
+
+# CHECK-LABEL: <high>:
+# CHECK-NEXT:    2002000: blr
+
+.section .text_low, "ax", %progbits
+.globl _start
+_start:
+  bl high@notoc
+  blr
+
+.section .text_high, "ax", %progbits
+.ifdef HIDDEN
+.hidden high
+.endif
+.globl high
+high:
+  blr