[lld][AArch64][ELF][PAC] Support `.relr.auth.dyn` section (#87635)

Support `R_AARCH64_AUTH_RELATIVE` relocation compression as described in
https://github.com/ARM-software/abi-aa/blob/main/pauthabielf64/pauthabielf64.rst#relocation-compression

6 files changed, 216 insertions, 47 deletions

diff --git a/lld/ELF/Arch/AArch64.cpp b/lld/ELF/Arch/AArch64.cpp
index 2bf6e2c..b0aa0b9 100644
--- a/lld/ELF/Arch/AArch64.cpp
+++ b/lld/ELF/Arch/AArch64.cpp
@@ -428,6 +428,19 @@ void AArch64::relocate(uint8_t *loc, const Relocation &rel,
   case R_AARCH64_PREL64:
     write64(loc, val);
     break;
+  case R_AARCH64_AUTH_ABS64:
+    // If val is wider than 32 bits, the relocation must have been moved from
+    // .relr.auth.dyn to .rela.dyn, and the addend write is not needed.
+    //
+    // If val fits in 32 bits, we have two potential scenarios:
+    // * True RELR: Write the 32-bit `val`.
+    // * RELA: Even if the value now fits in 32 bits, it might have been
+    //   converted from RELR during an iteration in
+    //   finalizeAddressDependentContent(). Writing the value is harmless
+    //   because dynamic linking ignores it.
+    if (isInt<32>(val))
+      write32(loc, val);
+    break;
   case R_AARCH64_ADD_ABS_LO12_NC:
     or32AArch64Imm(loc, val);
     break;
diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index 04db413..2c02c2e 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -898,9 +898,9 @@ static void addRelativeReloc(InputSectionBase &isec, uint64_t offsetInSec,
     isec.addReloc({expr, type, offsetInSec, addend, &sym});
     if (shard)
       part.relrDyn->relocsVec[parallel::getThreadIndex()].push_back(
-          {&isec, offsetInSec});
+          {&isec, isec.relocs().size() - 1});
     else
-      part.relrDyn->relocs.push_back({&isec, offsetInSec});
+      part.relrDyn->relocs.push_back({&isec, isec.relocs().size() - 1});
     return;
   }
   part.relaDyn->addRelativeReloc<shard>(target->relativeRel, isec, offsetInSec,
@@ -1154,6 +1154,12 @@ void RelocationScanner::processAux(RelExpr expr, RelType type, uint64_t offset,
         // relative relocation. Use a symbolic relocation instead.
         if (sym.isPreemptible) {
           part.relaDyn->addSymbolReloc(type, *sec, offset, sym, addend, type);
+        } else if (part.relrAuthDyn && sec->addralign >= 2 && offset % 2 == 0) {
+          // When symbol values are determined in
+          // finalizeAddressDependentContent, some .relr.auth.dyn relocations
+          // may be moved to .rela.dyn.
+          sec->addReloc({expr, type, offset, addend, &sym});
+          part.relrAuthDyn->relocs.push_back({sec, sec->relocs().size() - 1});
         } else {
           part.relaDyn->addReloc({R_AARCH64_AUTH_RELATIVE, sec, offset,
                                   DynamicReloc::AddendOnlyWithTargetVA, sym,
diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 298c714..22bfed0 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -1420,6 +1420,12 @@ DynamicSection<ELFT>::computeContents() {
     addInt(config->useAndroidRelrTags ? DT_ANDROID_RELRENT : DT_RELRENT,
            sizeof(Elf_Relr));
   }
+  if (part.relrAuthDyn && part.relrAuthDyn->getParent() &&
+      !part.relrAuthDyn->relocs.empty()) {
+    addInSec(DT_AARCH64_AUTH_RELR, *part.relrAuthDyn);
+    addInt(DT_AARCH64_AUTH_RELRSZ, part.relrAuthDyn->getParent()->size);
+    addInt(DT_AARCH64_AUTH_RELRENT, sizeof(Elf_Relr));
+  }
   if (isMain && in.relaPlt->isNeeded()) {
     addInSec(DT_JMPREL, *in.relaPlt);
     entries.emplace_back(DT_PLTRELSZ, addPltRelSz());
@@ -1731,10 +1737,13 @@ template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *buf) {
   }
 }
 
-RelrBaseSection::RelrBaseSection(unsigned concurrency)
-    : SyntheticSection(SHF_ALLOC,
-                       config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR,
-                       config->wordsize, ".relr.dyn"),
+RelrBaseSection::RelrBaseSection(unsigned concurrency, bool isAArch64Auth)
+    : SyntheticSection(
+          SHF_ALLOC,
+          isAArch64Auth
+              ? SHT_AARCH64_AUTH_RELR
+              : (config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR),
+          config->wordsize, isAArch64Auth ? ".relr.auth.dyn" : ".relr.dyn"),
       relocsVec(concurrency) {}
 
 void RelrBaseSection::mergeRels() {
@@ -2002,8 +2011,8 @@ bool AndroidPackedRelocationSection<ELFT>::updateAllocSize() {
 }
 
 template <class ELFT>
-RelrSection<ELFT>::RelrSection(unsigned concurrency)
-    : RelrBaseSection(concurrency) {
+RelrSection<ELFT>::RelrSection(unsigned concurrency, bool isAArch64Auth)
+    : RelrBaseSection(concurrency, isAArch64Auth) {
   this->entsize = config->wordsize;
 }
 
@@ -4774,6 +4783,9 @@ template <class ELFT> void elf::createSyntheticSections() {
     if (config->relrPackDynRelocs) {
       part.relrDyn = std::make_unique<RelrSection<ELFT>>(threadCount);
       add(*part.relrDyn);
+      part.relrAuthDyn = std::make_unique<RelrSection<ELFT>>(
+          threadCount, /*isAArch64Auth=*/true);
+      add(*part.relrAuthDyn);
     }
 
     if (!config->relocatable) {
diff --git a/lld/ELF/SyntheticSections.h b/lld/ELF/SyntheticSections.h
index 34949025..eaa09ea 100644
--- a/lld/ELF/SyntheticSections.h
+++ b/lld/ELF/SyntheticSections.h
@@ -548,7 +548,9 @@ public:
   static bool classof(const SectionBase *d) {
     return SyntheticSection::classof(d) &&
            (d->type == llvm::ELF::SHT_RELA || d->type == llvm::ELF::SHT_REL ||
-            d->type == llvm::ELF::SHT_RELR);
+            d->type == llvm::ELF::SHT_RELR ||
+            (d->type == llvm::ELF::SHT_AARCH64_AUTH_RELR &&
+             config->emachine == llvm::ELF::EM_AARCH64));
   }
   int32_t dynamicTag, sizeDynamicTag;
   SmallVector<DynamicReloc, 0> relocs;
@@ -596,15 +598,17 @@ private:
 };
 
 struct RelativeReloc {
-  uint64_t getOffset() const { return inputSec->getVA(offsetInSec); }
+  uint64_t getOffset() const {
+    return inputSec->getVA(inputSec->relocs()[relocIdx].offset);
+  }
 
   const InputSectionBase *inputSec;
-  uint64_t offsetInSec;
+  size_t relocIdx;
 };
 
 class RelrBaseSection : public SyntheticSection {
 public:
-  RelrBaseSection(unsigned concurrency);
+  RelrBaseSection(unsigned concurrency, bool isAArch64Auth = false);
   void mergeRels();
   bool isNeeded() const override {
     return !relocs.empty() ||
@@ -622,7 +626,7 @@ template <class ELFT> class RelrSection final : public RelrBaseSection {
   using Elf_Relr = typename ELFT::Relr;
 
 public:
-  RelrSection(unsigned concurrency);
+  RelrSection(unsigned concurrency, bool isAArch64Auth = false);
 
   bool updateAllocSize() override;
   size_t getSize() const override { return relrRelocs.size() * this->entsize; }
@@ -1460,6 +1464,7 @@ struct Partition {
   std::unique_ptr<PackageMetadataNote> packageMetadataNote;
   std::unique_ptr<RelocationBaseSection> relaDyn;
   std::unique_ptr<RelrBaseSection> relrDyn;
+  std::unique_ptr<RelrBaseSection> relrAuthDyn;
   std::unique_ptr<VersionDefinitionSection> verDef;
   std::unique_ptr<SyntheticSection> verNeed;
   std::unique_ptr<VersionTableSection> verSym;
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index e8a7b19..fe2e190 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -1454,9 +1454,32 @@ template <class ELFT> void Writer<ELFT>::finalizeAddressDependentContent() {
       in.mipsGot->updateAllocSize();
 
     for (Partition &part : partitions) {
+      // The R_AARCH64_AUTH_RELATIVE has a smaller addend field as bits [63:32]
+      // encode the signing schema. We've put relocations in .relr.auth.dyn
+      // during RelocationScanner::processAux, but the target VA for some of
+      // them might be wider than 32 bits. We can only know the final VA at this
+      // point, so move relocations with large values from .relr.auth.dyn to
+      // .rela.dyn. See also AArch64::relocate.
+      if (part.relrAuthDyn) {
+        auto it = llvm::remove_if(
+            part.relrAuthDyn->relocs, [&part](const RelativeReloc &elem) {
+              const Relocation &reloc = elem.inputSec->relocs()[elem.relocIdx];
+              if (isInt<32>(reloc.sym->getVA(reloc.addend)))
+                return false;
+              part.relaDyn->addReloc({R_AARCH64_AUTH_RELATIVE, elem.inputSec,
+                                      reloc.offset,
+                                      DynamicReloc::AddendOnlyWithTargetVA,
+                                      *reloc.sym, reloc.addend, R_ABS});
+              return true;
+            });
+        changed |= (it != part.relrAuthDyn->relocs.end());
+        part.relrAuthDyn->relocs.erase(it, part.relrAuthDyn->relocs.end());
+      }
       changed |= part.relaDyn->updateAllocSize();
       if (part.relrDyn)
         changed |= part.relrDyn->updateAllocSize();
+      if (part.relrAuthDyn)
+        changed |= part.relrAuthDyn->updateAllocSize();
       if (part.memtagGlobalDescriptors)
         changed |= part.memtagGlobalDescriptors->updateAllocSize();
     }
@@ -1614,6 +1637,14 @@ static void removeUnusedSyntheticSections() {
         auto *sec = cast<SyntheticSection>(s);
         if (sec->getParent() && sec->isNeeded())
           return false;
+        // .relr.auth.dyn relocations may be moved to .rela.dyn in
+        // finalizeAddressDependentContent, making .rela.dyn no longer empty.
+        // Conservatively keep .rela.dyn. .relr.auth.dyn can be made empty, but
+        // we would fail to remove it here.
+        if (config->emachine == EM_AARCH64 && config->relrPackDynRelocs)
+          if (auto *relSec = dyn_cast<RelocationBaseSection>(sec))
+            if (relSec == mainPart->relaDyn.get())
+              return false;
         unused.insert(sec);
         return true;
       });
@@ -1926,6 +1957,10 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
         part.relrDyn->mergeRels();
         finalizeSynthetic(part.relrDyn.get());
       }
+      if (part.relrAuthDyn) {
+        part.relrAuthDyn->mergeRels();
+        finalizeSynthetic(part.relrAuthDyn.get());
+      }
 
       finalizeSynthetic(part.dynSymTab.get());
       finalizeSynthetic(part.gnuHashTab.get());
diff --git a/lld/test/ELF/aarch64-reloc-pauth.s b/lld/test/ELF/aarch64-reloc-pauth.s
index b603d8f..f1ce29e 100644
--- a/lld/test/ELF/aarch64-reloc-pauth.s
+++ b/lld/test/ELF/aarch64-reloc-pauth.s
@@ -1,11 +1,13 @@
 # REQUIRES: aarch64
 
-# RUN: llvm-mc -filetype=obj -triple=aarch64 %p/Inputs/shared2.s -o %t.a.o
-# RUN: ld.lld -shared %t.a.o -soname=so -o %t.a.so
-# RUN: llvm-mc -filetype=obj -triple=aarch64 %s -o %t.o
+# RUN: rm -rf %t && split-file %s %t && cd %t
 
-# RUN: ld.lld -pie %t.o %t.a.so -o %t
-# RUN: llvm-readobj -r %t | FileCheck --check-prefix=UNPACKED %s
+# RUN: llvm-mc -filetype=obj -triple=aarch64 %p/Inputs/shared2.s -o a.o
+# RUN: ld.lld -shared a.o -soname=so -o a.so
+# RUN: llvm-mc -filetype=obj -triple=aarch64 main.s -o main.o
+
+# RUN: ld.lld -pie main.o a.so -o main
+# RUN: llvm-readobj -r main | FileCheck --check-prefix=UNPACKED %s
 
 # UNPACKED:          Section ({{.+}}) .rela.dyn {
 # UNPACKED-NEXT:       0x30470 R_AARCH64_AUTH_RELATIVE - 0x1
@@ -21,8 +23,8 @@
 # UNPACKED-NEXT:       0x304B0 R_AARCH64_AUTH_ABS64 bar2 0x0
 # UNPACKED-NEXT:     }
 
-# RUN: ld.lld %t.o %t.a.so -o %t.nopie
-# RUN: llvm-readobj -r %t.nopie | FileCheck --check-prefix=NOPIE %s
+# RUN: ld.lld main.o a.so -o main.nopie
+# RUN: llvm-readobj -r main.nopie | FileCheck --check-prefix=NOPIE %s
 
 # NOPIE:      Section ({{.+}}) .rela.dyn {
 # NOPIE:        0x230460 R_AARCH64_AUTH_RELATIVE - 0x200001
@@ -38,67 +40,95 @@
 # NOPIE-NEXT:   0x2304A0 R_AARCH64_AUTH_ABS64 bar2 0x0
 # NOPIE-NEXT: }
 
-# RUN: ld.lld -pie %t.o %t.a.so -o %t.pie
-# RUN: llvm-readelf -S -d -r -x .test %t.pie | FileCheck --check-prefixes=PIE,HEX %s
-
-# PIE:      Section Headers:
-# PIE-NEXT: Name Type Address Off Size ES Flg Lk Inf Al
-# PIE:      .rela.dyn RELA {{0*}}[[#%x,ADDR1:]]
-# PIE-SAME:                                     {{0*}}[[#ADDR1]] 000108 18 A 1 0 8
-
-# PIE:      Relocation section '.rela.dyn' at offset 0x[[#ADDR1]] contains 11 entries:
-# PIE-NEXT:     Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
-# PIE-NEXT: 0000000000030470  0000000000000411 R_AARCH64_AUTH_RELATIVE 1
-# PIE-NEXT: 0000000000030478  0000000000000411 R_AARCH64_AUTH_RELATIVE 30472
-# PIE-NEXT: 0000000000030480  0000000000000411 R_AARCH64_AUTH_RELATIVE fffffffffffffffd
-# PIE-NEXT: 0000000000030488  0000000000000411 R_AARCH64_AUTH_RELATIVE 12345678
-# PIE-NEXT: 0000000000030490  0000000000000411 R_AARCH64_AUTH_RELATIVE 123456789a
-# PIE-NEXT: 0000000000030498  0000000000000411 R_AARCH64_AUTH_RELATIVE ffffffedcba98766
-# PIE-NEXT: 00000000000304a0  0000000000000411 R_AARCH64_AUTH_RELATIVE 8003046f
-# PIE-NEXT: 00000000000304b9  0000000000000411 R_AARCH64_AUTH_RELATIVE 4
-# PIE-NEXT: 00000000000304c2  0000000000000411 R_AARCH64_AUTH_RELATIVE 30475
-# PIE-NEXT: 00000000000304a8  0000000100000244 R_AARCH64_AUTH_ABS64   0000000000000000 zed2 + 1111
-# PIE-NEXT: 00000000000304b0  0000000200000244 R_AARCH64_AUTH_ABS64   0000000000000000 bar2 + 0
+# RUN: ld.lld -pie -z pack-relative-relocs main.o a.so -o main.pie
+# RUN: llvm-readelf -S -d -r -x .test main.pie | FileCheck --check-prefixes=RELR,HEX %s
+
+# RELR:      Section Headers:
+# RELR-NEXT: Name Type Address Off Size ES Flg Lk Inf Al
+# RELR:      .rela.dyn RELA {{0*}}[[ADDR1:.+]] {{0*}}[[ADDR1]] 000090 18 A 1 0 8
+# RELR:      .relr.auth.dyn AARCH64_AUTH_RELR {{0*}}[[ADDR2:.+]] {{0*}}[[ADDR2]] 000018 08 A 0 0 8
+
+# RELR:      Dynamic section at offset {{.+}} contains 16 entries
+# RELR:      0x0000000070000012 (AARCH64_AUTH_RELR) 0x[[ADDR2]]
+# RELR-NEXT: 0x0000000070000011 (AARCH64_AUTH_RELRSZ) 24 (bytes)
+# RELR-NEXT: 0x0000000070000013 (AARCH64_AUTH_RELRENT) 8 (bytes)
+
+## Decoded SHT_RELR section is same as UNPACKED,
+## but contains only the relative relocations.
+## Any relative relocations with odd offset or value wider than 32 bits stay in SHT_RELA.
+
+# RELR:      Relocation section '.rela.dyn' at offset 0x[[ADDR1]] contains 6 entries:
+# RELR-NEXT:     Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
+# RELR-NEXT: 0000000000030460  0000000000000411 R_AARCH64_AUTH_RELATIVE           123456789a
+# RELR-NEXT: 0000000000030468  0000000000000411 R_AARCH64_AUTH_RELATIVE           ffffffedcba98766
+# RELR-NEXT: 0000000000030470  0000000000000411 R_AARCH64_AUTH_RELATIVE           8003043f
+# RELR-NEXT: 0000000000030489  0000000000000411 R_AARCH64_AUTH_RELATIVE           4
+# RELR-NEXT: 0000000000030478  0000000100000244 R_AARCH64_AUTH_ABS64   0000000000000000 zed2 + 1111
+# RELR-NEXT: 0000000000030480  0000000200000244 R_AARCH64_AUTH_ABS64   0000000000000000 bar2 + 0
+# RELR-EMPTY:
+# RELR-NEXT: Relocation section '.relr.auth.dyn' at offset 0x[[ADDR2]] contains 5 entries:
+# RELR-NEXT: Index: Entry Address Symbolic Address
+# RELR-NEXT: 0000: 0000000000030440 0000000000030440 $d.0
+# RELR-NEXT: 0001: 000000000000000f 0000000000030448 $d.0 + 0x8
+# RELR-NEXT:  0000000000030450 $d.0 + 0x10
+# RELR-NEXT:  0000000000030458 $d.0 + 0x18
+# RELR-NEXT: 0002: 0000000000030492 0000000000030492 $d.0 + 0x52
 
 # HEX:      Hex dump of section '.test':
-# HEX-NEXT: 0x00030470 00000000 2a000020 00000000 2b000000
+# HEX-NEXT: 0x00030440 01000000 2a000020 42040300 2b000000
+##                     ^^^^^^^^ Implicit val = 1 = __ehdr_start + 1
 ##                              ^^^^ Discr = 42
 ##                                    ^^ Key (bits 5..6) = DA
+##                                       ^^^^^^^^ Implicit val = 0x30442 = 0x30440 + 2 = .test + 2
 ##                                                ^^^^ Discr = 43
 ##                                                      ^^ Key (bits 5..6) = IA
-# HEX-NEXT: 0x00030480 00000000 2c000080 00000000 2d000020
+# HEX-NEXT: 0x00030450 fdffffff 2c000080 78563412 2d000020
+##                     ^^^^^^^^ Implicit val = -3 = __ehdr_start - 3
 ##                              ^^^^ Discr = 44
 ##                                    ^^ Key (bits 5..6) = IA
 ##                                    ^^ Addr diversity (bit 7) = true
+##                                       ^^^^^^^^ Implicit val = 0x12345678 = __ehdr_start + 0x12345678
 ##                                                ^^^^ Discr = 45
 ##                                                      ^^ Key (bits 5..6) = DA
-# HEX-NEXT: 0x00030490 00000000 2e000020 00000000 2f000020
+# HEX-NEXT: 0x00030460 00000000 2e000020 00000000 2f000020
+##                     ^^^^^^^^ No implicit val (rela reloc due val wider than 32 bits)
 ##                              ^^^^ Discr = 46
 ##                                    ^^ Key (bits 5..6) = DA
+##                                       ^^^^^^^^ No implicit val (rela reloc due to val wider than 32 bits)
 ##                                                ^^^^ Discr = 47
 ##                                                      ^^ Key (bits 5..6) = DA
-# HEX-NEXT: 0x000304a0 00000000 30000020 00000000 31000020
+# HEX-NEXT: 0x00030470 00000000 30000020 00000000 31000020
+##                     ^^^^^^^^ No implicit val (rela reloc due val wider than 32 bits)
 ##                              ^^^^ Discr = 48
 ##                                    ^^ Key (bits 5..6) = DA
+##                                       ^^^^^^^^ No implicit val (rela reloc due to a preemptible symbol)
 ##                                                ^^^^ Discr = 49
 ##                                                      ^^ Key (bits 5..6) = DA
-# HEX-NEXT: 0x000304b0 00000000 32000000 77000000 00330000
+# HEX-NEXT: 0x00030480 00000000 32000000 77000000 00330000
+##                     ^^^^^^^^ No implicit val (rela reloc due to a preemptible symbol)
 ##                              ^^^^ Discr = 50
 ##                                    ^^ Key (bits 5..6) = IA
+##                                         ^^^^^^ ^^ No implicit val (rela reloc due to odd offset)
 ##                                                  ^^^^ Discr = 51
-# HEX-NEXT: 0x000304c0 20770000 00003400 0020{{\ }}
+# HEX-NEXT: 0x00030490 20774504 03003400 0020{{\ }}
 ##                     ^^ Key (bits 5..6) = DA
+##                         ^^^^ ^^^^ Implicit val = 0x30445 = 0x30440 + 5 = .test + 5
 ##                                  ^^^^ Discr = 52
 ##                                         ^^ Key (bits 5..6) = DA
 
+#--- main.s
+
 .section .test, "aw"
 .p2align 3
 .quad (__ehdr_start + 1)@AUTH(da,42)
 .quad (.test + 2)@AUTH(ia,43)
 .quad (__ehdr_start - 3)@AUTH(ia,44,addr)
 .quad (__ehdr_start + 0x12345678)@AUTH(da,45)
+## Addend wider than 32 bits, not enough room for storing implicitly, would go to rela
 .quad (__ehdr_start + 0x123456789A)@AUTH(da,46)
+## Negative addend wider than 32 bits, not enough room for storing implicitly, would go to rela
 .quad (__ehdr_start - 0x123456789A)@AUTH(da,47)
+## INT32_MAX plus non-zero .test is wider than 32 bits, not enough room for storing implicitly, would go to rela
 .quad (.test + 0x7FFFFFFF)@AUTH(da,48)
 .quad (zed2 + 0x1111)@AUTH(da,49)
 .quad bar2@AUTH(ia,50)
@@ -106,3 +136,71 @@
 .quad (__ehdr_start + 4)@AUTH(da,51)
 .byte 0x77
 .quad (.test + 5)@AUTH(da,52)
+
+#--- empty-relr.s
+
+## .relr.auth.dyn relocations that do not fit 32 bits are moved to .rela.dyn.
+## In this case .relr.auth.dyn will be made empty, but
+## removeUnusedSyntheticSections fails to remove the section.
+
+# RUN: llvm-mc -filetype=obj -triple=aarch64 empty-relr.s -o empty-relr.o
+# RUN: ld.lld -pie -z pack-relative-relocs empty-relr.o -o empty-relr
+# RUN: llvm-readelf -S -d -r empty-relr | FileCheck --check-prefixes=EMPTY-RELR %s
+
+# EMPTY-RELR:      Section Headers:
+# EMPTY-RELR-NEXT: Name Type Address Off Size ES Flg Lk Inf Al
+# EMPTY-RELR:      .rela.dyn RELA {{0*}}[[ADDR1:.+]] {{0*}}[[ADDR1]] 000018 18 A 0 0 8
+# EMPTY-RELR:      .relr.auth.dyn AARCH64_AUTH_RELR {{0*}}[[ADDR2:.+]] {{0*}}[[ADDR2]] 000000 08 A 0 0 8
+
+# EMPTY-RELR:      Dynamic section at offset {{.+}} contains 12 entries
+# EMPTY-RELR-NOT:  (AARCH64_AUTH_RELR)
+# EMPTY-RELR-NOT:  (AARCH64_AUTH_RELRSZ)
+# EMPTY-RELR-NOT:  (AARCH64_AUTH_RELRENT)
+# EMPTY-RELR:      0x0000000000000007 (RELA) 0x[[ADDR1]]
+# EMPTY-RELR-NEXT: 0x0000000000000008 (RELASZ) 24 (bytes)
+# EMPTY-RELR-NEXT: 0x0000000000000009 (RELAENT) 24 (bytes)
+
+# EMPTY-RELR:      Relocation section '.rela.dyn' at offset {{.+}} contains 1 entries:
+# EMPTY-RELR-NEXT:     Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
+# EMPTY-RELR-NEXT: 0000000000030320  0000000000000411 R_AARCH64_AUTH_RELATIVE           8003031f
+# EMPTY-RELR-EMPTY:
+# EMPTY-RELR-NEXT: Relocation section '.relr.auth.dyn' at offset {{.+}} contains 0 entries:
+# EMPTY-RELR-NEXT: Index: Entry Address Symbolic Address
+
+.section .test, "aw"
+.p2align 3
+.quad (.test + 0x7FFFFFFF)@AUTH(da,42)
+
+#--- empty-rela.s
+
+## .relr.auth.dyn relocations that do not fit 32 bits are moved to .rela.dyn.
+## If this scenario does not happen, .rela.dyn will remain empty,
+## but removeUnusedSyntheticSections fails to remove the section.
+
+# RUN: llvm-mc -filetype=obj -triple=aarch64 empty-rela.s -o empty-rela.o
+# RUN: ld.lld -pie -z pack-relative-relocs empty-rela.o -o empty-rela
+# RUN: llvm-readelf -S -d -r empty-rela | FileCheck --check-prefixes=EMPTY-RELA %s
+
+# EMPTY-RELA:      Section Headers:
+# EMPTY-RELA-NEXT: Name Type Address Off Size ES Flg Lk Inf Al
+# EMPTY-RELA:      .rela.dyn RELA {{0*}}[[ADDR1:.+]] {{0*}}[[ADDR1]] 000000 18 A 0 0 8
+# EMPTY-RELA:      .relr.auth.dyn AARCH64_AUTH_RELR {{0*}}[[ADDR2:.+]] {{0*}}[[ADDR2]] 000008 08 A 0 0 8
+
+# EMPTY-RELA:      Dynamic section at offset {{.+}} contains 12 entries
+# EMPTY-RELA-NOT:  (RELR)
+# EMPTY-RELA-NOT:  (RELRSZ)
+# EMPTY-RELA-NOT:  (RELRENT)
+# EMPTY-RELA:      0x0000000070000012 (AARCH64_AUTH_RELR) 0x[[ADDR2]]
+# EMPTY-RELA-NEXT: 0x0000000070000011 (AARCH64_AUTH_RELRSZ) 8 (bytes)
+# EMPTY-RELA-NEXT: 0x0000000070000013 (AARCH64_AUTH_RELRENT) 8 (bytes)
+
+# EMPTY-RELA:      Relocation section '.rela.dyn' at offset {{.+}} contains 0 entries:
+# EMPTY-RELA-NEXT:     Offset             Info             Type               Symbol's Value  Symbol's Name
+# EMPTY-RELA-EMPTY:
+# EMPTY-RELA-NEXT: Relocation section '.relr.auth.dyn' at offset {{.+}} contains 1 entries:
+# EMPTY-RELA-NEXT: Index: Entry Address Symbolic Address
+# EMPTY-RELA-NEXT: 0000: 0000000000030310 0000000000030310 $d.0
+
+.section .test, "aw"
+.p2align 3
+.quad (.test + 0x12345678)@AUTH(da,42)