[llvm] r341419 - [llvm-strip] Allow copying relocation sections without symbol tables.

[Jordan Rupprecht via llvm-commits]

Author: rupprecht
Date: Tue Sep  4 15:28:49 2018
New Revision: 341419

URL: http://llvm.org/viewvc/llvm-project?rev=341419&view=rev
Log:
[llvm-strip] Allow copying relocation sections without symbol tables.

Summary:
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.
```

Reviewers: jakehehrlich, alexshap

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D51493

Added:
    llvm/trunk/test/tools/llvm-objcopy/reloc-no-symtab.test
Modified:
    llvm/trunk/tools/llvm-objcopy/Object.cpp

Added: llvm/trunk/test/tools/llvm-objcopy/reloc-no-symtab.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-objcopy/reloc-no-symtab.test?rev=341419&view=auto
==============================================================================
--- llvm/trunk/test/tools/llvm-objcopy/reloc-no-symtab.test (added)
+++ llvm/trunk/test/tools/llvm-objcopy/reloc-no-symtab.test Tue Sep  4 15:28:49 2018
@@ -0,0 +1,45 @@
+# 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.original | FileCheck %s
+# 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

Modified: llvm/trunk/tools/llvm-objcopy/Object.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objcopy/Object.cpp?rev=341419&r1=341418&r2=341419&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objcopy/Object.cpp (original)
+++ llvm/trunk/tools/llvm-objcopy/Object.cpp Tue Sep  4 15:28:49 2018
@@ -375,11 +375,13 @@ void RelocSectionWithSymtabBase<SymTabTy
 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 @@ void RelocSectionWithSymtabBase<SymTabTy
 
 template <class SymTabType>
 void RelocSectionWithSymtabBase<SymTabType>::finalize() {
-  this->Link = Symbols->Index;
+  this->Link = Symbols ? Symbols->Index : 0;
+
   if (SecToApplyRel != nullptr)
     this->Info = SecToApplyRel->Index;
 }