ELF: Have __rela_iplt_{start,end} surround .rela.iplt with --pack-dyn-relocs=android.

In #86751 we moved the IRELATIVE relocations to .rela.plt when
--pack-dyn-relocs=android was enabled but we neglected to also move
the __rela_iplt_{start,end} symbols. As a result, static binaries
linked with this flag were unable to find their IRELATIVE relocations.
Fix it by having the symbols surround the correct section.

Reviewers: MaskRay, smithp35

Reviewed By: MaskRay

Pull Request: https://github.com/llvm/llvm-project/pull/118585

lld/ELF/Relocations.cpp

@@ -1687,6 +1687,17 @@ template <class ELFT> void elf::scanRelocations(Ctx &ctx) {
     outerFn();
 }
 
+RelocationBaseSection &elf::getIRelativeSection(Ctx &ctx) {
+  // Prior to Android V, there was a bug that caused RELR relocations to be
+  // applied after packed relocations. This meant that resolvers referenced by
+  // IRELATIVE relocations in the packed relocation section would read
+  // unrelocated globals with RELR relocations when
+  // --pack-relative-relocs=android+relr is enabled. Work around this by placing
+  // IRELATIVE in .rela.plt.
+  return ctx.arg.androidPackDynRelocs ? *ctx.in.relaPlt
+                                      : *ctx.mainPart->relaDyn;
+}
+
 static bool handleNonPreemptibleIfunc(Ctx &ctx, Symbol &sym, uint16_t flags) {
   // Handle a reference to a non-preemptible ifunc. These are special in a
   // few ways:
@@ -1736,17 +1747,9 @@ static bool handleNonPreemptibleIfunc(Ctx &ctx, Symbol &sym, uint16_t flags) {
   // original section/value pairs. For non-GOT non-PLT relocation case below, we
   // may alter section/value, so create a copy of the symbol to make
   // section/value fixed.
-  //
-  // Prior to Android V, there was a bug that caused RELR relocations to be
-  // applied after packed relocations. This meant that resolvers referenced by
-  // IRELATIVE relocations in the packed relocation section would read
-  // unrelocated globals with RELR relocations when
-  // --pack-relative-relocs=android+relr is enabled. Work around this by placing
-  // IRELATIVE in .rela.plt.
   auto *directSym = makeDefined(cast<Defined>(sym));
   directSym->allocateAux(ctx);
-  auto &dyn =
-      ctx.arg.androidPackDynRelocs ? *ctx.in.relaPlt : *ctx.mainPart->relaDyn;
+  auto &dyn = getIRelativeSection(ctx);
   addPltEntry(ctx, *ctx.in.iplt, *ctx.in.igotPlt, dyn, ctx.target->iRelativeRel,
               *directSym);
   sym.allocateAux(ctx);

lld/ELF/Relocations.h

@@ -22,6 +22,7 @@ class Symbol;
 class InputSection;
 class InputSectionBase;
 class OutputSection;
+class RelocationBaseSection;
 class SectionBase;
 
 // Represents a relocation type, such as R_X86_64_PC32 or R_ARM_THM_CALL.
@@ -356,6 +357,8 @@ sortRels(Relocs<llvm::object::Elf_Crel_Impl<is64>> rels,
   return {};
 }
 
+RelocationBaseSection &getIRelativeSection(Ctx &ctx);
+
 // Returns true if Expr refers a GOT entry. Note that this function returns
 // false for TLS variables even though they need GOT, because TLS variables uses
 // GOT differently than the regular variables.

lld/ELF/Writer.cpp

@@ -844,11 +844,15 @@ template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
     ctx.sym.globalOffsetTable->section = sec;
   }
 
-  // .rela_iplt_{start,end} mark the start and the end of .rel[a].dyn.
-  if (ctx.sym.relaIpltStart && ctx.mainPart->relaDyn->isNeeded()) {
-    ctx.sym.relaIpltStart->section = ctx.mainPart->relaDyn.get();
-    ctx.sym.relaIpltEnd->section = ctx.mainPart->relaDyn.get();
-    ctx.sym.relaIpltEnd->value = ctx.mainPart->relaDyn->getSize();
+  // .rela_iplt_{start,end} mark the start and the end of the section containing
+  // IRELATIVE relocations.
+  if (ctx.sym.relaIpltStart) {
+    auto &dyn = getIRelativeSection(ctx);
+    if (dyn.isNeeded()) {
+      ctx.sym.relaIpltStart->section = &dyn;
+      ctx.sym.relaIpltEnd->section = &dyn;
+      ctx.sym.relaIpltEnd->value = dyn.getSize();
+    }
   }
 
   PhdrEntry *last = nullptr;

lld/test/ELF/pack-dyn-relocs-ifunc.s

@@ -47,3 +47,28 @@ _start:
 .globl bar
 bar:
   ret
+
+#--- c.s
+
+# RUN: llvm-mc -filetype=obj -triple=aarch64-linux-android c.s -o c.o
+# RUN: ld.lld --pack-dyn-relocs=android c.o -o c
+# RUN: llvm-readelf -sS c | FileCheck --check-prefix=STATIC %s
+
+# STATIC: .rela.plt         RELA            0000000000200158 000158 000018 18  AI  0   5  8
+# STATIC: 0000000000200158     0 NOTYPE  LOCAL  HIDDEN      1 __rela_iplt_start
+# STATIC: 0000000000200170     0 NOTYPE  LOCAL  HIDDEN      1 __rela_iplt_end
+
+.text
+.type foo, %gnu_indirect_function
+.globl foo
+foo:
+  ret
+
+.globl _start
+_start:
+  bl foo
+
+.data
+.balign 8
+.quad __rela_iplt_start
+.quad __rela_iplt_end