[PATCH] D51493: [llvm-strip] Allow copying relocation sections without symbol tables.

[Jordan Rupprecht via Phabricator via llvm-commits]

rupprecht created this revision.
rupprecht added a reviewer: jakehehrlich.
Herald added a reviewer: alexshap.
Herald added a subscriber: llvm-commits.

Fixes the error "Link field value 0 in section .rela.plt is invalid" when copying/stripping certain binaries. Minimal repro:

  $ cat /tmp/a.c
  int main() { return 0; }
  $ clang -static /tmp/a.c -o /tmp/a
  $ llvm-strip /tmp/a -o /tmp/b
  llvm-strip: error: Link field value 0 in section .rela.plt is invalid.


Repository:
  rL LLVM

https://reviews.llvm.org/D51493

Files:
  test/tools/llvm-objcopy/reloc-no-symtab.test
  tools/llvm-objcopy/Object.cpp


Index: tools/llvm-objcopy/Object.cpp
===================================================================
--- tools/llvm-objcopy/Object.cpp
+++ tools/llvm-objcopy/Object.cpp
@@ -375,11 +375,13 @@
 template <class SymTabType>
 void RelocSectionWithSymtabBase<SymTabType>::initialize(
     SectionTableRef SecTable) {
-  setSymTab(SecTable.getSectionOfType<SymTabType>(
-      Link,
-      "Link field value " + Twine(Link) + " in section " + Name + " is invalid",
-      "Link field value " + Twine(Link) + " in section " + Name +
-          " is not a symbol table"));
+  if (Link != SHN_UNDEF)
+    setSymTab(SecTable.getSectionOfType<SymTabType>(
+        Link,
+        "Link field value " + Twine(Link) + " in section " + Name +
+            " is invalid",
+        "Link field value " + Twine(Link) + " in section " + Name +
+            " is not a symbol table"));
 
   if (Info != SHN_UNDEF)
     setSection(SecTable.getSection(Info, "Info field value " + Twine(Info) +
@@ -391,7 +393,8 @@
 
 template <class SymTabType>
 void RelocSectionWithSymtabBase<SymTabType>::finalize() {
-  this->Link = Symbols->Index;
+  if (Symbols != nullptr)
+    this->Link = Symbols->Index;
   if (SecToApplyRel != nullptr)
     this->Info = SecToApplyRel->Index;
 }
Index: test/tools/llvm-objcopy/reloc-no-symtab.test
===================================================================
--- /dev/null
+++ test/tools/llvm-objcopy/reloc-no-symtab.test
@@ -0,0 +1,44 @@
+# Regression test for the following case:
+# $ cat /tmp/a.c
+# int main() { return 0; }
+# $ clang -static /tmp/a.c -o /tmp/a
+# $ llvm-strip /tmp/a -o /tmp/b
+# llvm-strip: error: Link field value 0 in section .rela.plt is invalid.
+
+# RUN: yaml2obj %s > %t.original
+# RUN: llvm-strip %t.original -o %t.stripped
+# RUN: llvm-readobj -sections %t.stripped | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:          .text
+    Type:          SHT_PROGBITS
+    Flags:         [ SHF_ALLOC, SHF_EXECINSTR ]
+  - Name:          .rela.plt
+    Type:          SHT_RELA
+    Flags:         [ SHF_ALLOC, SHF_INFO_LINK ]
+    Info:          .got.plt
+    Link:          0
+  - Name:          .plt
+    Type:          SHT_PROGBITS
+    Flags:         [ SHF_ALLOC, SHF_EXECINSTR ]
+  - Name:          .got.plt
+    Type:          SHT_PROGBITS
+    Flags:         [ SHF_ALLOC, SHF_WRITE ]
+
+# CHECK:      Name: .rela.plt
+# CHECK-NEXT: Type: SHT_RELA
+# CHECK-NEXT: Flags [
+# CHECK-NEXT:   SHF_ALLOC
+# CHECK-NEXT:   SHF_INFO_LINK
+# CHECK-NEXT: ]
+# CHECK-NEXT: Address:
+# CHECK-NEXT: Offset:
+# CHECK-NEXT: Size: 0
+# CHECK-NEXT: Link: 0
+# CHECK-NEXT: Info: 4


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