[lld] [ELF] --pack-dyn-relocs=android: place IRELATIVE in .rela.dyn (PR #86751)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay created https://github.com/llvm/llvm-project/pull/86751

None

>From 40f0b099b1ac002143f9f6a3313afcd8f049086a Mon Sep 17 00:00:00 2001
From: Fangrui Song <i at maskray.me>
Date: Tue, 26 Mar 2024 17:01:50 -0700
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
 =?UTF-8?q?l=20version?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Created using spr 1.3.5-bogner
---
 lld/ELF/Relocations.cpp              | 10 +++++--
 lld/test/ELF/pack-dyn-relocs-ifunc.s | 43 ++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)
 create mode 100644 lld/test/ELF/pack-dyn-relocs-ifunc.s

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index 33c50133bec495..2ffb40c5fa4398 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -1659,10 +1659,16 @@ static bool handleNonPreemptibleIfunc(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
+  // IRELATIVE relocations in the packed relocation section could not read
+  // globals with RELR relocations. Work around this by placing IRELATIVE in
+  // .rela.plt.
   auto *directSym = makeDefined(cast<Defined>(sym));
   directSym->allocateAux();
-  addPltEntry(*in.iplt, *in.igotPlt, *mainPart->relaDyn, target->iRelativeRel,
-              *directSym);
+  auto &dyn = config->androidPackDynRelocs ? *in.relaPlt : *mainPart->relaDyn;
+  addPltEntry(*in.iplt, *in.igotPlt, dyn, target->iRelativeRel, *directSym);
   sym.allocateAux();
   symAux.back().pltIdx = symAux[directSym->auxIdx].pltIdx;
 
diff --git a/lld/test/ELF/pack-dyn-relocs-ifunc.s b/lld/test/ELF/pack-dyn-relocs-ifunc.s
new file mode 100644
index 00000000000000..ada771aa08ace3
--- /dev/null
+++ b/lld/test/ELF/pack-dyn-relocs-ifunc.s
@@ -0,0 +1,43 @@
+# REQUIRES: aarch64
+## Prior to Android V, there was a bug that caused RELR relocations to be
+## applied after packed relocations. This meant that resolvers referenced
+## IRELATIVE relocations in the packed relocation section could not read
+## globals with RELR relocations. Work around this by placing IRELATIVE in
+## .rela.plt
+
+# RUN: rm -rf %t && split-file %s %t && cd %t
+# RUN: llvm-mc -filetype=obj -triple=aarch64-linux-android a.s -o a.o
+# RUN: llvm-mc -filetype=obj -triple=aarch64-linux-android b.s -o b.o
+# RUN: ld.lld -shared b.o -o b.so
+# RUN: ld.lld --pack-dyn-relocs=android -z separate-loadable-segments a.o b.so -o a
+# RUN: llvm-readobj -r a | FileCheck %s
+# RUN: llvm-objdump -d a | FileCheck %s --check-prefix=ASM
+
+# CHECK:      .rela.plt {
+# CHECK-NEXT:   0x230020 R_AARCH64_JUMP_SLOT bar 0x0
+# CHECK-NEXT:   0x230028 R_AARCH64_IRELATIVE - {{.*}}
+# CHECK-NEXT: }
+
+# ASM:      <.iplt>:
+# ASM-NEXT: adrp    x16, 0x230000
+# ASM-NEXT: ldr     x17, [x16, #0x28]
+
+#--- a.s
+.text
+.type foo, %gnu_indirect_function
+.globl foo
+foo:
+  ret
+
+.globl _start
+_start:
+  bl foo
+  bl bar
+
+.data
+.quad .data
+
+#--- b.s
+.globl bar
+bar:
+  ret