[llvm-objcopy][llvm-strip] Add switch to allow removing referenced sections
llvm-objcopy currently emits an error if a section to be removed is
referenced by another section. This is a reasonable thing to do, but is
different to GNU objcopy. We should allow users who know what they are
doing to have a way to produce the invalid ELF. This change adds a new
switch --allow-broken-links to both llvm-strip and llvm-objcopy to do
precisely that. The corresponding sh_link field is then set to 0 instead
of an error being emitted.
I cannot use llvm-readelf/readobj to test the link fields because they
emit an error if any sections, like the .dynsym, cannot be properly
loaded.
Reviewed by: rupprecht, grimar
Differential Revision: https://reviews.llvm.org/D60324
llvm-svn: 358649
diff --git a/llvm/tools/llvm-objcopy/ELF/Object.cpp b/llvm/tools/llvm-objcopy/ELF/Object.cpp
index 979ab0a..f5452ce 100644
--- a/llvm/tools/llvm-objcopy/ELF/Object.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/Object.cpp
@@ -51,6 +51,7 @@
}
Error SectionBase::removeSectionReferences(
+ bool AllowBrokenLinks,
function_ref<bool(const SectionBase *)> ToRemove) {
return Error::success();
}
@@ -424,14 +425,19 @@
}
Error SymbolTableSection::removeSectionReferences(
+ bool AllowBrokenLinks,
function_ref<bool(const SectionBase *)> ToRemove) {
if (ToRemove(SectionIndexTable))
SectionIndexTable = nullptr;
- if (ToRemove(SymbolNames))
- return createStringError(llvm::errc::invalid_argument,
- "String table %s cannot be removed because it is "
- "referenced by the symbol table %s",
- SymbolNames->Name.data(), this->Name.data());
+ if (ToRemove(SymbolNames)) {
+ if (!AllowBrokenLinks)
+ return createStringError(
+ llvm::errc::invalid_argument,
+ "String table %s cannot be removed because it is "
+ "referenced by the symbol table %s",
+ SymbolNames->Name.data(), this->Name.data());
+ SymbolNames = nullptr;
+ }
return removeSymbols(
[ToRemove](const Symbol &Sym) { return ToRemove(Sym.DefinedIn); });
}
@@ -476,12 +482,13 @@
void SymbolTableSection::finalize() {
uint32_t MaxLocalIndex = 0;
for (auto &Sym : Symbols) {
- Sym->NameIndex = SymbolNames->findIndex(Sym->Name);
+ Sym->NameIndex =
+ SymbolNames == nullptr ? 0 : SymbolNames->findIndex(Sym->Name);
if (Sym->Binding == STB_LOCAL)
MaxLocalIndex = std::max(MaxLocalIndex, Sym->Index);
}
// Now we need to set the Link and Info fields.
- Link = SymbolNames->Index;
+ Link = SymbolNames == nullptr ? 0 : SymbolNames->Index;
Info = MaxLocalIndex + 1;
}
@@ -491,10 +498,14 @@
// indexes later in fillShdnxTable.
if (SectionIndexTable)
SectionIndexTable->reserve(Symbols.size());
+
// Add all of our strings to SymbolNames so that SymbolNames has the right
// size before layout is decided.
- for (auto &Sym : Symbols)
- SymbolNames->addString(Sym->Name);
+ // If the symbol names section has been removed, don't try to add strings to
+ // the table.
+ if (SymbolNames != nullptr)
+ for (auto &Sym : Symbols)
+ SymbolNames->addString(Sym->Name);
}
void SymbolTableSection::fillShndxTable() {
@@ -548,12 +559,17 @@
}
Error RelocationSection::removeSectionReferences(
+ bool AllowBrokenLinks,
function_ref<bool(const SectionBase *)> ToRemove) {
- if (ToRemove(Symbols))
- 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());
+ 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;
+ }
for (const Relocation &R : Relocations) {
if (!R.RelocSymbol->DefinedIn || !ToRemove(R.RelocSymbol->DefinedIn))
@@ -667,13 +683,16 @@
Visitor.visit(*this);
}
-Error Section::removeSectionReferences(
+Error Section::removeSectionReferences(bool AllowBrokenDependency,
function_ref<bool(const SectionBase *)> ToRemove) {
- if (ToRemove(LinkSection))
- return createStringError(llvm::errc::invalid_argument,
- "Section %s cannot be removed because it is "
- "referenced by the section %s",
- LinkSection->Name.data(), this->Name.data());
+ if (ToRemove(LinkSection)) {
+ if (!AllowBrokenDependency)
+ return createStringError(llvm::errc::invalid_argument,
+ "Section %s cannot be removed because it is "
+ "referenced by the section %s",
+ LinkSection->Name.data(), this->Name.data());
+ LinkSection = nullptr;
+ }
return Error::success();
}
@@ -1387,7 +1406,7 @@
ELFWriter<ELFT>::ELFWriter(Object &Obj, Buffer &Buf, bool WSH)
: Writer(Obj, Buf), WriteSectionHeaders(WSH && Obj.HadShdrs) {}
-Error Object::removeSections(
+Error Object::removeSections(bool AllowBrokenLinks,
std::function<bool(const SectionBase &)> ToRemove) {
auto Iter = std::stable_partition(
@@ -1423,7 +1442,7 @@
// a live section critically depends on a section being removed somehow
// (e.g. the removed section is referenced by a relocation).
for (auto &KeepSec : make_range(std::begin(Sections), Iter)) {
- if (Error E = KeepSec->removeSectionReferences(
+ if (Error E = KeepSec->removeSectionReferences(AllowBrokenLinks,
[&RemoveSections](const SectionBase *Sec) {
return RemoveSections.find(Sec) != RemoveSections.end();
}))
@@ -1629,9 +1648,11 @@
// Since we don't need SectionIndexTable we should remove it and all
// references to it.
if (Obj.SectionIndexTable != nullptr) {
- if (Error E = Obj.removeSections([this](const SectionBase &Sec) {
- return &Sec == Obj.SectionIndexTable;
- }))
+ // We do not support sections referring to the section index table.
+ if (Error E = Obj.removeSections(false /*AllowBrokenLinks*/,
+ [this](const SectionBase &Sec) {
+ return &Sec == Obj.SectionIndexTable;
+ }))
return E;
}
}