From af90d54660dae0fdd61e918e3d2d797e255c7c7d Mon Sep 17 00:00:00 2001
From: George Rimar <grimar@accesssoftek.com>
Date: Mon, 2 May 2016 13:49:42 +0000
Subject: [PATCH] [ELF] - keep alive all non-text sections referenced by
 .eh_frame
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

Patch implements one of suggestions from Rafael Ávila de Espíndola,
to fix segfault after section that contains personality being
garbage collected.

Suggestion was just to keep alive all non executable sections
referenced by .eh_frame.

This fixes PR27529.

Differential revision: http://reviews.llvm.org/D19656

llvm-svn: 268228
---
 lld/ELF/MarkLive.cpp       | 51 ++++++++++++++++++++++++++++++++--------------
 lld/test/ELF/eh-frame-gc.s | 20 ++++++++++++++++++
 2 files changed, 56 insertions(+), 15 deletions(-)
 create mode 100644 lld/test/ELF/eh-frame-gc.s

diff --git a/lld/ELF/MarkLive.cpp b/lld/ELF/MarkLive.cpp
index 0c9fedb..b605269 100644
--- a/lld/ELF/MarkLive.cpp
+++ b/lld/ELF/MarkLive.cpp
@@ -61,7 +61,8 @@ static typename ELFT::uint getAddend(InputSectionBase<ELFT> *Sec,
 }
 
 template <class ELFT, class RelT>
-static ResolvedReloc<ELFT> resolveReloc(InputSection<ELFT> *Sec, RelT &Rel) {
+static ResolvedReloc<ELFT> resolveReloc(InputSectionBase<ELFT> *Sec,
+                                        RelT &Rel) {
   SymbolBody &B = Sec->getFile()->getRelocTargetSym(Rel);
   auto *D = dyn_cast<DefinedRegular<ELFT>>(&B);
   if (!D || !D->Section)
@@ -72,24 +73,38 @@ static ResolvedReloc<ELFT> resolveReloc(InputSection<ELFT> *Sec, RelT &Rel) {
   return {D->Section->Repl, Offset};
 }
 
+template <class ELFT, class Elf_Shdr>
+static void run(ELFFile<ELFT> &Obj, InputSectionBase<ELFT> *Sec,
+                Elf_Shdr *RelSec, std::function<void(ResolvedReloc<ELFT>)> Fn) {
+  if (RelSec->sh_type == SHT_RELA) {
+    for (const typename ELFT::Rela &RI : Obj.relas(RelSec))
+      Fn(resolveReloc(Sec, RI));
+  } else {
+    for (const typename ELFT::Rel &RI : Obj.rels(RelSec))
+      Fn(resolveReloc(Sec, RI));
+  }
+}
+
 // Calls Fn for each section that Sec refers to via relocations.
 template <class ELFT>
 static void forEachSuccessor(InputSection<ELFT> *Sec,
                              std::function<void(ResolvedReloc<ELFT>)> Fn) {
-  typedef typename ELFT::Rel Elf_Rel;
-  typedef typename ELFT::Rela Elf_Rela;
-  typedef typename ELFT::Shdr Elf_Shdr;
-
   ELFFile<ELFT> &Obj = Sec->getFile()->getObj();
-  for (const Elf_Shdr *RelSec : Sec->RelocSections) {
-    if (RelSec->sh_type == SHT_RELA) {
-      for (const Elf_Rela &RI : Obj.relas(RelSec))
-        Fn(resolveReloc(Sec, RI));
-    } else {
-      for (const Elf_Rel &RI : Obj.rels(RelSec))
-        Fn(resolveReloc(Sec, RI));
-    }
-  }
+  for (const typename ELFT::Shdr *RelSec : Sec->RelocSections)
+    run(Obj, Sec, RelSec, Fn);
+}
+
+template <class ELFT> static void scanEhFrameSection(EHInputSection<ELFT> &EH) {
+  if (!EH.RelocSection)
+    return;
+  ELFFile<ELFT> &EObj = EH.getFile()->getObj();
+  run<ELFT>(EObj, &EH, EH.RelocSection, [&](ResolvedReloc<ELFT> R) {
+    if (!R.Sec || R.Sec == &InputSection<ELFT>::Discarded)
+      return;
+    if (R.Sec->getSectionHdr()->sh_flags & SHF_EXECINSTR)
+      return;
+    R.Sec->Live = true;
+  });
 }
 
 // Sections listed below are special because they are used by the loader
@@ -160,9 +175,15 @@ template <class ELFT> void elf::markLive(SymbolTable<ELFT> *Symtab) {
   // script KEEP command.
   for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab->getObjectFiles())
     for (InputSectionBase<ELFT> *Sec : F->getSections())
-      if (Sec && Sec != &InputSection<ELFT>::Discarded)
+      if (Sec && Sec != &InputSection<ELFT>::Discarded) {
+        // .eh_frame is always marked as live now, but also it can reference to
+        // sections that contain personality. We preserve all non-text sections
+        // referred by .eh_frame here.
+        if (auto *EH = dyn_cast_or_null<EHInputSection<ELFT>>(Sec))
+          scanEhFrameSection<ELFT>(*EH);
         if (isReserved(Sec) || Script<ELFT>::X->shouldKeep(Sec))
           Enqueue({Sec, 0});
+      }
 
   // Mark all reachable sections.
   while (!Q.empty())
diff --git a/lld/test/ELF/eh-frame-gc.s b/lld/test/ELF/eh-frame-gc.s
new file mode 100644
index 0000000..b2e21f4
--- /dev/null
+++ b/lld/test/ELF/eh-frame-gc.s
@@ -0,0 +1,20 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=i686-pc-linux %s -o %t.o
+# RUN: ld.lld -shared --gc-sections %t.o -o %t
+# RUN: llvm-readobj  -s %t | FileCheck %s
+
+## Check that section containing personality is
+## not garbage collected.
+# CHECK: Sections [
+# CHECK: Name: .test_personality_section
+
+.text
+.globl foo
+.type foo,@function
+foo:
+ .cfi_startproc
+ .cfi_personality 155, DW.ref.__gxx_personality_v0
+ .cfi_endproc
+
+.section .test_personality_section
+DW.ref.__gxx_personality_v0:
-- 
2.7.4