[llvm-objcopy] - Check dynamic relocation sections for broken references.

This is a fix for https://bugs.llvm.org/show_bug.cgi?id=41371.

Currently, it is possible to break the sh_link field of the dynamic relocation section
by removing the section it refers to. The patch fixes an issue and adds 2 test cases.

One of them shows that it does not seem possible to break the sh_info field.
I added an assert to verify this.

Differential revision: https://reviews.llvm.org/D60825

llvm-svn: 359552

1 files changed, 27 insertions, 6 deletions

diff --git a/llvm/tools/llvm-objcopy/ELF/Object.cpp b/llvm/tools/llvm-objcopy/ELF/Object.cpp
index 3830f92..60163b6 100644
--- a/llvm/tools/llvm-objcopy/ELF/Object.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/Object.cpp
@@ -680,12 +680,33 @@ void DynamicRelocationSection::accept(SectionVisitor &Visitor) const {
 }
 
 void DynamicRelocationSection::accept(MutableSectionVisitor &Visitor) {
-  Visitor.visit(*this);
-}
-
-Error Section::removeSectionReferences(bool AllowBrokenDependency,
-    function_ref<bool(const SectionBase *)> ToRemove) {
-  if (ToRemove(LinkSection)) {
+  Visitor.visit(*this);

+}

+

+Error DynamicRelocationSection::removeSectionReferences(

+    bool AllowBrokenLinks, function_ref<bool(const SectionBase *)> ToRemove) {

+  if (ToRemove(Symbols)) {

+    if (!AllowBrokenLinks)

+      return createStringError(

+          llvm::errc::invalid_argument,

+          "Symbol table %s cannot be removed because it is "

+          "referenced by the relocation section %s.",

+          Symbols->Name.data(), this->Name.data());

+    Symbols = nullptr;

+  }

+

+  // SecToApplyRel contains a section referenced by sh_info field. It keeps

+  // a section to which the relocation section applies. When we remove any

+  // sections we also remove their relocation sections. Since we do that much

+  // earlier, this assert should never be triggered.

+  assert(!SecToApplyRel || !ToRemove(SecToApplyRel));

+

+  return Error::success();

+}

+

+Error Section::removeSectionReferences(bool AllowBrokenDependency,

+    function_ref<bool(const SectionBase *)> ToRemove) {

+  if (ToRemove(LinkSection)) {

     if (!AllowBrokenDependency)
       return createStringError(llvm::errc::invalid_argument,
                                "Section %s cannot be removed because it is "