[llvm] r315412 - [llvm-objcopy] Add support for --strip-sections to remove all section headers leaving only program headers and loadable segment data
Jake Ehrlich via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 10 18:59:06 PDT 2017
Author: jakehehrlich
Date: Tue Oct 10 18:59:06 2017
New Revision: 315412
URL: http://llvm.org/viewvc/llvm-project?rev=315412&view=rev
Log:
[llvm-objcopy] Add support for --strip-sections to remove all section headers leaving only program headers and loadable segment data
elf utils implements a particularly extreme form of stripping that I'd
like to support. eu-strip has an option called "strip-sections" that
removes all section headers and leaves only program headers and the
segment data. I have implemented this option partly as a test but mainly
because in Fuchsia we would like to use this option to minimize the size
of our executables. The other strip options that are on my list include
--strip-all and --strip-debug. This is a preliminary implementation that
I'd like to start using in Fuchsia builds if possible. This change
implements such a stripping option for llvm-objcopy
Differential Revision: https://reviews.llvm.org/D38335
Added:
llvm/trunk/test/tools/llvm-objcopy/strip-sections.test
Modified:
llvm/trunk/tools/llvm-objcopy/Object.cpp
llvm/trunk/tools/llvm-objcopy/Object.h
llvm/trunk/tools/llvm-objcopy/llvm-objcopy.cpp
Added: llvm/trunk/test/tools/llvm-objcopy/strip-sections.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-objcopy/strip-sections.test?rev=315412&view=auto
==============================================================================
--- llvm/trunk/test/tools/llvm-objcopy/strip-sections.test (added)
+++ llvm/trunk/test/tools/llvm-objcopy/strip-sections.test Tue Oct 10 18:59:06 2017
@@ -0,0 +1,66 @@
+# RUN: yaml2obj %s > %t
+# RUN: llvm-objcopy --strip-sections %t %t2
+# RUN: llvm-readobj -file-headers -program-headers %t2 | FileCheck %s
+# RUN: od -t x1 -j 4096 %t2 | FileCheck %s --check-prefix=DATA
+
+!ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_X86_64
+Sections:
+ - Name: .text
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ AddressAlign: 0x0000000000001000
+ Content: "DEADBEEF"
+ProgramHeaders:
+- Type: PT_LOAD
+ Flags: [ PF_X, PF_R ]
+ Sections:
+ - Section: .text
+
+#DATA: 0010000 de ad be ef
+
+#CHECK: ElfHeader {
+#CHECK-NEXT: Ident {
+#CHECK-NEXT: Magic: (7F 45 4C 46)
+#CHECK-NEXT: Class: 64-bit (0x2)
+#CHECK-NEXT: DataEncoding: LittleEndian (0x1)
+#CHECK-NEXT: FileVersion: 1
+#CHECK-NEXT: OS/ABI: SystemV (0x0)
+#CHECK-NEXT: ABIVersion: 0
+#CHECK-NEXT: Unused: (00 00 00 00 00 00 00)
+#CHECK-NEXT: }
+#CHECK-NEXT: Type: Executable (0x2)
+#CHECK-NEXT: Machine: EM_X86_64 (0x3E)
+#CHECK-NEXT: Version: 1
+#CHECK-NEXT: Entry: 0x0
+#CHECK-NEXT: ProgramHeaderOffset: 0x40
+#CHECK-NEXT: SectionHeaderOffset: 0x0
+#CHECK-NEXT: Flags [ (0x0)
+#CHECK-NEXT: ]
+#CHECK-NEXT: HeaderSize: 64
+#CHECK-NEXT: ProgramHeaderEntrySize: 56
+#CHECK-NEXT: ProgramHeaderCount: 1
+#CHECK-NEXT: SectionHeaderEntrySize: 64
+#CHECK-NEXT: SectionHeaderCount: 0
+#CHECK-NEXT: StringTableSectionIndex: 0
+#CHECK-NEXT: }
+
+#CHECK: ProgramHeaders [
+#CHECK-NEXT: ProgramHeader {
+#CHECK-NEXT: Type: PT_LOAD (0x1)
+#CHECK-NEXT: Offset: 0x1000
+#CHECK-NEXT: VirtualAddress: 0x0
+#CHECK-NEXT: PhysicalAddress: 0x0
+#CHECK-NEXT: FileSize: 4
+#CHECK-NEXT: MemSize: 4
+#CHECK-NEXT: Flags [ (0x5)
+#CHECK-NEXT: PF_R (0x4)
+#CHECK-NEXT: PF_X (0x1)
+#CHECK-NEXT: ]
+#CHECK-NEXT: Alignment: 4096
+#CHECK-NEXT: }
+#CHECK-NEXT:]
Modified: llvm/trunk/tools/llvm-objcopy/Object.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objcopy/Object.cpp?rev=315412&r1=315411&r2=315412&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objcopy/Object.cpp (original)
+++ llvm/trunk/tools/llvm-objcopy/Object.cpp Tue Oct 10 18:59:06 2017
@@ -575,14 +575,20 @@ void Object<ELFT>::writeHeader(FileOutpu
Ehdr.e_version = Version;
Ehdr.e_entry = Entry;
Ehdr.e_phoff = sizeof(Elf_Ehdr);
- Ehdr.e_shoff = SHOffset;
Ehdr.e_flags = Flags;
Ehdr.e_ehsize = sizeof(Elf_Ehdr);
Ehdr.e_phentsize = sizeof(Elf_Phdr);
Ehdr.e_phnum = Segments.size();
Ehdr.e_shentsize = sizeof(Elf_Shdr);
- Ehdr.e_shnum = Sections.size() + 1;
- Ehdr.e_shstrndx = SectionNames->Index;
+ if (WriteSectionHeaders) {
+ Ehdr.e_shoff = SHOffset;
+ Ehdr.e_shnum = Sections.size() + 1;
+ Ehdr.e_shstrndx = SectionNames->Index;
+ } else {
+ Ehdr.e_shoff = 0;
+ Ehdr.e_shnum = 0;
+ Ehdr.e_shstrndx = 0;
+ }
}
template <class ELFT>
@@ -633,12 +639,10 @@ void Object<ELFT>::removeSections(
if (SymbolTable != nullptr && ToRemove(*SymbolTable))
SymbolTable = nullptr;
if (ToRemove(*SectionNames)) {
- // Right now llvm-objcopy always outputs section headers. This will not
- // always be the case. Eventully the section header table will become
- // optional and if no section header is output then there dosn't need to be
- // a section header string table.
- error("Cannot remove " + SectionNames->Name +
- " because it is the section header string table.");
+ if (WriteSectionHeaders)
+ error("Cannot remove " + SectionNames->Name +
+ " because it is the section header string table.");
+ SectionNames = nullptr;
}
// Now make sure there are no remaining references to the sections that will
// be removed. Sometimes it is impossible to remove a reference so we emit
@@ -732,29 +736,34 @@ template <class ELFT> void ELFObject<ELF
}
}
- Offset = alignTo(Offset, sizeof(typename ELFT::Addr));
+ if (this->WriteSectionHeaders) {
+ Offset = alignTo(Offset, sizeof(typename ELFT::Addr));
+ }
this->SHOffset = Offset;
}
template <class ELFT> size_t ELFObject<ELFT>::totalSize() const {
// We already have the section header offset so we can calculate the total
// size by just adding up the size of each section header.
+ auto NullSectionSize = this->WriteSectionHeaders ? sizeof(Elf_Shdr) : 0;
return this->SHOffset + this->Sections.size() * sizeof(Elf_Shdr) +
- sizeof(Elf_Shdr);
+ NullSectionSize;
}
template <class ELFT> void ELFObject<ELFT>::write(FileOutputBuffer &Out) const {
this->writeHeader(Out);
this->writeProgramHeaders(Out);
this->writeSectionData(Out);
- this->writeSectionHeaders(Out);
+ if (this->WriteSectionHeaders)
+ this->writeSectionHeaders(Out);
}
template <class ELFT> void ELFObject<ELFT>::finalize() {
// Make sure we add the names of all the sections.
- for (const auto &Section : this->Sections) {
- this->SectionNames->addString(Section->Name);
- }
+ if (this->SectionNames != nullptr)
+ for (const auto &Section : this->Sections) {
+ this->SectionNames->addString(Section->Name);
+ }
// Make sure we add the names of all the symbols.
if (this->SymbolTable != nullptr)
this->SymbolTable->addSymbolNames();
@@ -763,14 +772,16 @@ template <class ELFT> void ELFObject<ELF
assignOffsets();
// Finalize SectionNames first so that we can assign name indexes.
- this->SectionNames->finalize();
+ if (this->SectionNames != nullptr)
+ this->SectionNames->finalize();
// Finally now that all offsets and indexes have been set we can finalize any
// remaining issues.
uint64_t Offset = this->SHOffset + sizeof(Elf_Shdr);
for (auto &Section : this->Sections) {
Section->HeaderOffset = Offset;
Offset += sizeof(Elf_Shdr);
- Section->NameIndex = this->SectionNames->findIndex(Section->Name);
+ if (this->WriteSectionHeaders)
+ Section->NameIndex = this->SectionNames->findIndex(Section->Name);
Section->finalize();
}
}
Modified: llvm/trunk/tools/llvm-objcopy/Object.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objcopy/Object.h?rev=315412&r1=315411&r2=315412&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objcopy/Object.h (original)
+++ llvm/trunk/tools/llvm-objcopy/Object.h Tue Oct 10 18:59:06 2017
@@ -346,6 +346,7 @@ public:
uint32_t Machine;
uint32_t Version;
uint32_t Flags;
+ bool WriteSectionHeaders = true;
Object(const llvm::object::ELFObjectFile<ELFT> &Obj);
void removeSections(std::function<bool(const SectionBase &)> ToRemove);
Modified: llvm/trunk/tools/llvm-objcopy/llvm-objcopy.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objcopy/llvm-objcopy.cpp?rev=315412&r1=315411&r2=315412&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objcopy/llvm-objcopy.cpp (original)
+++ llvm/trunk/tools/llvm-objcopy/llvm-objcopy.cpp Tue Oct 10 18:59:06 2017
@@ -56,11 +56,14 @@ cl::opt<std::string> OutputFilename(cl::
cl::opt<std::string>
OutputFormat("O", cl::desc("set output format to one of the following:"
"\n\tbinary"));
-
cl::list<std::string> ToRemove("remove-section",
cl::desc("Remove a specific section"));
cl::alias ToRemoveA("R", cl::desc("Alias for remove-section"),
cl::aliasopt(ToRemove));
+cl::opt<bool> StripSections("strip-sections",
+ cl::desc("Remove all section headers"));
+
+typedef std::function<bool(const SectionBase &Sec)> SectionPred;
void CopyBinary(const ELFObjectFile<ELF64LE> &ObjFile) {
std::unique_ptr<FileOutputBuffer> Buffer;
@@ -71,12 +74,25 @@ void CopyBinary(const ELFObjectFile<ELF6
Obj = llvm::make_unique<BinaryObject<ELF64LE>>(ObjFile);
else
Obj = llvm::make_unique<ELFObject<ELF64LE>>(ObjFile);
+
+ SectionPred RemovePred = [](const SectionBase &) { return false; };
+
if (!ToRemove.empty()) {
- Obj->removeSections([&](const SectionBase &Sec) {
+ RemovePred = [&](const SectionBase &Sec) {
return std::find(std::begin(ToRemove), std::end(ToRemove), Sec.Name) !=
std::end(ToRemove);
- });
+ };
}
+
+ if (StripSections) {
+ RemovePred = [RemovePred](const SectionBase &Sec) {
+ return RemovePred(Sec) || (Sec.Flags & SHF_ALLOC) == 0;
+ };
+ Obj->WriteSectionHeaders = false;
+ }
+
+ Obj->removeSections(RemovePred);
+
Obj->finalize();
ErrorOr<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
FileOutputBuffer::create(OutputFilename, Obj->totalSize(),
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