[PATCH] D48929: [ELF] Update addends in non-allocatable sections for REL targets when creating a relocatable output.

[Igor Kudrin via Phabricator via llvm-commits]

ikudrin created this revision.
ikudrin added a reviewer: ruiu.
ikudrin added a project: lld.
Herald added subscribers: MaskRay, JDevlieghere, arichardson, aprantl, emaste.
Herald added a reviewer: espindola.

This fixes PR37735.

As addends were not updated in that case, the debug information in the relocatable output became corrupted.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D48929

Files:
  ELF/InputSection.cpp
  ELF/InputSection.h
  test/ELF/pr37735.s


Index: test/ELF/pr37735.s
===================================================================
--- /dev/null
+++ test/ELF/pr37735.s
@@ -0,0 +1,12 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=i386-pc-linux-gnu %s -o %t.o
+# RUN: ld.lld -r %t.o %t.o -o %t1.o
+# RUN: llvm-objdump -s -section=.bar %t1.o | FileCheck %s
+
+.section .foo
+	.byte 0
+
+# CHECK:      Contents of section .bar:
+# CHECK-NEXT:  0000 00000000 01000000
+.section .bar
+	.dc.a .foo
Index: ELF/InputSection.h
===================================================================
--- ELF/InputSection.h
+++ ELF/InputSection.h
@@ -179,6 +179,7 @@
   // the mmap'ed output buffer.
   template <class ELFT> void relocate(uint8_t *Buf, uint8_t *BufEnd);
   void relocateAlloc(uint8_t *Buf, uint8_t *BufEnd);
+  void relocateNonAllocForRelocatable(uint8_t *Buf, uint8_t *BufEnd);
 
   // The native ELF reloc data type is not very convenient to handle.
   // So we convert ELF reloc records to our own records in Relocations.cpp.
Index: ELF/InputSection.cpp
===================================================================
--- ELF/InputSection.cpp
+++ ELF/InputSection.cpp
@@ -734,6 +734,11 @@
     return;
   }
 
+  if (Config->Relocatable) {
+    relocateNonAllocForRelocatable(Buf, BufEnd);
+    return;
+  }
+
   auto *Sec = cast<InputSection>(this);
   if (Sec->AreRelocsRela)
     Sec->relocateNonAlloc<ELFT>(Buf, Sec->template relas<ELFT>());
@@ -804,6 +809,30 @@
   }
 }
 
+// This is used when '-r' is given.
+// For REL targets, InputSection::copyRelocations() may store artificial
+// relocations aimed to update addends. They are handled in relocateAlloc()
+// for allocatable sections, and this method does the same for non-allocatable
+// sections, such as sections with debug information.
+void InputSectionBase::relocateNonAllocForRelocatable(uint8_t *Buf,
+                                                      uint8_t *BufEnd) {
+  const unsigned Bits = Config->Wordsize * 8;
+
+  for (const Relocation &Rel : Relocations) {
+    // InputSection::copyRelocations() adds only R_ABS relocations.
+    // We don't expect to see here anything else.
+    assert(Rel.Expr == R_ABS);
+
+    auto *Sec = cast<InputSection>(this);
+    uint64_t Offset = Rel.Offset + Sec->OutSecOff;
+    uint8_t *BufLoc = Buf + Offset;
+    RelType Type = Rel.Type;
+    uint64_t TargetVA = SignExtend64(Rel.Sym->getVA(Rel.Addend), Bits);
+
+    Target->relocateOne(BufLoc, Type, TargetVA);
+  }
+}
+
 template <class ELFT> void InputSection::writeTo(uint8_t *Buf) {
   if (Type == SHT_NOBITS)
     return;


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