From 87575f6501dc4c1ae27e3bd6a469fa0391964a2b Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <peter@pcc.me.uk>
Date: Wed, 29 May 2019 04:06:01 +0000
Subject: [PATCH] ELF: Don't reuse a thunk in a different loadable partition.

There's no guarantee that the other partition will be loaded, so it
can't be reused.

Differential Revision: https://reviews.llvm.org/D62365

llvm-svn: 361926
---
 lld/ELF/Relocations.cpp              | 19 +++++++++++----
 lld/ELF/Relocations.h                |  3 ++-
 lld/test/ELF/partition-thunk-reuse.s | 45 ++++++++++++++++++++++++++++++++++++
 3 files changed, 62 insertions(+), 5 deletions(-)
 create mode 100644 lld/test/ELF/partition-thunk-reuse.s

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index aab5385..b02e1cc 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -1607,12 +1607,22 @@ ThunkSection *ThunkCreator::addThunkSection(OutputSection *OS,
                                             InputSectionDescription *ISD,
                                             uint64_t Off) {
   auto *TS = make<ThunkSection>(OS, Off);
+  TS->Partition = OS->Partition;
   ISD->ThunkSections.push_back({TS, Pass});
   return TS;
 }
 
-std::pair<Thunk *, bool> ThunkCreator::getThunk(Symbol &Sym, RelType Type,
-                                                uint64_t Src) {
+static bool isThunkSectionCompatible(InputSection *Source,
+                                     SectionBase *Target) {
+  // We can't reuse thunks in different loadable partitions because they might
+  // not be loaded. But partition 1 (the main partition) will always be loaded.
+  if (Source->Partition != Target->Partition)
+    return Target->Partition == 1;
+  return true;
+}
+
+std::pair<Thunk *, bool> ThunkCreator::getThunk(InputSection *IS, Symbol &Sym,
+                                                RelType Type, uint64_t Src) {
   std::vector<Thunk *> *ThunkVec = nullptr;
 
   // We use (section, offset) pair to find the thunk position if possible so
@@ -1625,7 +1635,8 @@ std::pair<Thunk *, bool> ThunkCreator::getThunk(Symbol &Sym, RelType Type,
 
   // Check existing Thunks for Sym to see if they can be reused
   for (Thunk *T : *ThunkVec)
-    if (T->isCompatibleWith(Type) &&
+    if (isThunkSectionCompatible(IS, T->getThunkTargetSym()->Section) &&
+        T->isCompatibleWith(Type) &&
         Target->inBranchRange(Type, Src, T->getThunkTargetSym()->getVA()))
       return std::make_pair(T, false);
 
@@ -1709,7 +1720,7 @@ bool ThunkCreator::createThunks(ArrayRef<OutputSection *> OutputSections) {
 
             Thunk *T;
             bool IsNew;
-            std::tie(T, IsNew) = getThunk(*Rel.Sym, Rel.Type, Src);
+            std::tie(T, IsNew) = getThunk(IS, *Rel.Sym, Rel.Type, Src);
 
             if (IsNew) {
               // Find or create a ThunkSection for the new Thunk
diff --git a/lld/ELF/Relocations.h b/lld/ELF/Relocations.h
index 923aa46..00156f5 100644
--- a/lld/ELF/Relocations.h
+++ b/lld/ELF/Relocations.h
@@ -136,7 +136,8 @@ private:
 
   void createInitialThunkSections(ArrayRef<OutputSection *> OutputSections);
 
-  std::pair<Thunk *, bool> getThunk(Symbol &Sym, RelType Type, uint64_t Src);
+  std::pair<Thunk *, bool> getThunk(InputSection *IS, Symbol &Sym, RelType Type,
+                                    uint64_t Src);
 
   ThunkSection *addThunkSection(OutputSection *OS, InputSectionDescription *,
                                 uint64_t Off);
diff --git a/lld/test/ELF/partition-thunk-reuse.s b/lld/test/ELF/partition-thunk-reuse.s
new file mode 100644
index 0000000..6425bdf
--- /dev/null
+++ b/lld/test/ELF/partition-thunk-reuse.s
@@ -0,0 +1,45 @@
+// REQUIRES: arm
+// RUN: llvm-mc %s -o %t.o -filetype=obj --triple=armv7-unknown-linux -arm-add-build-attributes
+// RUN: ld.lld %t.o -o %t --export-dynamic --gc-sections
+// RUN: llvm-nm %t | FileCheck %s
+
+// CHECK: __Thumbv7ABSLongThunk__start
+// CHECK: __Thumbv7ABSLongThunk__start
+
+// CHECK: __Thumbv7ABSLongThunk_foo
+// CHECK-NOT: __Thumbv7ABSLongThunk_foo
+
+.thumb
+
+.section .llvm_sympart.g1,"",%llvm_sympart
+.asciz "part1"
+.4byte f1
+
+.section .llvm_sympart.g2,"",%llvm_sympart
+.asciz "part2"
+.4byte f2
+
+.section .text._start,"ax",%progbits
+.globl _start
+_start:
+bx lr
+foo:
+b f0
+.zero 17*1048576
+
+.section .text.f0,"ax",%progbits
+.globl f0
+f0:
+b foo
+
+.section .text.f1,"aw",%progbits
+.globl f1
+f1:
+b _start
+b foo
+
+.section .text.f2,"ax",%progbits
+.globl f2
+f2:
+b _start
+b foo
-- 
2.7.4