Reland "[LLVM][llvm-objcopy] Added basic plumbing to get things started"
As discussed on llvm-dev I've implemented the first basic steps towards
llvm-objcopy/llvm-objtool (name pending).
This change adds the ability to copy (without modification) 64-bit
little endian ELF executables that have SHT_PROGBITS, SHT_NOBITS,
SHT_NULL and SHT_STRTAB sections.
Patch by Jake Ehrlich
Differential Revision: https://reviews.llvm.org/D33964
llvm-svn: 309643
diff --git a/llvm/tools/llvm-objcopy/Object.cpp b/llvm/tools/llvm-objcopy/Object.cpp
new file mode 100644
index 0000000..77ac8d9
--- /dev/null
+++ b/llvm/tools/llvm-objcopy/Object.cpp
@@ -0,0 +1,341 @@
+//===- Object.cpp -----------------------------------------------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#include "Object.h"
+#include "llvm-objcopy.h"
+
+using namespace llvm;
+using namespace object;
+using namespace ELF;
+
+template <class ELFT> void Segment::writeHeader(FileOutputBuffer &Out) const {
+ typedef typename ELFT::Ehdr Elf_Ehdr;
+ typedef typename ELFT::Phdr Elf_Phdr;
+
+ uint8_t *Buf = Out.getBufferStart();
+ Buf += sizeof(Elf_Ehdr) + Index * sizeof(Elf_Phdr);
+ Elf_Phdr &Phdr = *reinterpret_cast<Elf_Phdr *>(Buf);
+ Phdr.p_type = Type;
+ Phdr.p_flags = Flags;
+ Phdr.p_offset = Offset;
+ Phdr.p_vaddr = VAddr;
+ Phdr.p_paddr = PAddr;
+ Phdr.p_filesz = FileSize;
+ Phdr.p_memsz = MemSize;
+ Phdr.p_align = Align;
+}
+
+void Segment::finalize() {
+ auto FirstSec = firstSection();
+ if (FirstSec) {
+ // It is possible for a gap to be at the begining of a segment. Because of
+ // this we need to compute the new offset based on how large this gap was
+ // in the source file. Section layout should have already ensured that this
+ // space is not used for something else.
+ uint64_t OriginalOffset = Offset;
+ Offset = FirstSec->Offset - (FirstSec->OriginalOffset - OriginalOffset);
+ }
+}
+
+void SectionBase::finalize() {}
+
+template <class ELFT>
+void SectionBase::writeHeader(FileOutputBuffer &Out) const {
+ uint8_t *Buf = Out.getBufferStart();
+ Buf += HeaderOffset;
+ typename ELFT::Shdr &Shdr = *reinterpret_cast<typename ELFT::Shdr *>(Buf);
+ Shdr.sh_name = NameIndex;
+ Shdr.sh_type = Type;
+ Shdr.sh_flags = Flags;
+ Shdr.sh_addr = Addr;
+ Shdr.sh_offset = Offset;
+ Shdr.sh_size = Size;
+ Shdr.sh_link = Link;
+ Shdr.sh_info = Info;
+ Shdr.sh_addralign = Align;
+ Shdr.sh_entsize = EntrySize;
+}
+
+void Section::writeSection(FileOutputBuffer &Out) const {
+ if (Type == SHT_NOBITS)
+ return;
+ uint8_t *Buf = Out.getBufferStart() + Offset;
+ std::copy(std::begin(Contents), std::end(Contents), Buf);
+}
+
+void StringTableSection::addString(StringRef Name) {
+ StrTabBuilder.add(Name);
+ Size = StrTabBuilder.getSize();
+}
+
+uint32_t StringTableSection::findIndex(StringRef Name) const {
+ return StrTabBuilder.getOffset(Name);
+}
+
+void StringTableSection::finalize() { StrTabBuilder.finalize(); }
+
+void StringTableSection::writeSection(FileOutputBuffer &Out) const {
+ StrTabBuilder.write(Out.getBufferStart() + Offset);
+}
+
+// Returns true IFF a section is wholly inside the range of a segment
+static bool sectionWithinSegment(const SectionBase &Section,
+ const Segment &Segment) {
+ // If a section is empty it should be treated like it has a size of 1. This is
+ // to clarify the case when an empty section lies on a boundary between two
+ // segments and ensures that the section "belongs" to the second segment and
+ // not the first.
+ uint64_t SecSize = Section.Size ? Section.Size : 1;
+ return Segment.Offset <= Section.OriginalOffset &&
+ Segment.Offset + Segment.FileSize >= Section.OriginalOffset + SecSize;
+}
+
+template <class ELFT>
+void Object<ELFT>::readProgramHeaders(const ELFFile<ELFT> &ElfFile) {
+ uint32_t Index = 0;
+ for (const auto &Phdr : unwrapOrError(ElfFile.program_headers())) {
+ Segments.emplace_back(llvm::make_unique<Segment>());
+ Segment &Seg = *Segments.back();
+ Seg.Type = Phdr.p_type;
+ Seg.Flags = Phdr.p_flags;
+ Seg.Offset = Phdr.p_offset;
+ Seg.VAddr = Phdr.p_vaddr;
+ Seg.PAddr = Phdr.p_paddr;
+ Seg.FileSize = Phdr.p_filesz;
+ Seg.MemSize = Phdr.p_memsz;
+ Seg.Align = Phdr.p_align;
+ Seg.Index = Index++;
+ for (auto &Section : Sections) {
+ if (sectionWithinSegment(*Section, Seg)) {
+ Seg.addSection(&*Section);
+ if (!Section->ParentSegment ||
+ Section->ParentSegment->Offset > Seg.Offset) {
+ Section->ParentSegment = &Seg;
+ }
+ }
+ }
+ }
+}
+
+template <class ELFT>
+std::unique_ptr<SectionBase>
+Object<ELFT>::makeSection(const llvm::object::ELFFile<ELFT> &ElfFile,
+ const Elf_Shdr &Shdr) {
+ ArrayRef<uint8_t> Data;
+ switch (Shdr.sh_type) {
+ case SHT_STRTAB:
+ return llvm::make_unique<StringTableSection>();
+ case SHT_NOBITS:
+ return llvm::make_unique<Section>(Data);
+ default:
+ Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
+ return llvm::make_unique<Section>(Data);
+ };
+}
+
+template <class ELFT>
+void Object<ELFT>::readSectionHeaders(const ELFFile<ELFT> &ElfFile) {
+ uint32_t Index = 0;
+ for (const auto &Shdr : unwrapOrError(ElfFile.sections())) {
+ if (Index == 0) {
+ ++Index;
+ continue;
+ }
+ SecPtr Sec = makeSection(ElfFile, Shdr);
+ Sec->Name = unwrapOrError(ElfFile.getSectionName(&Shdr));
+ Sec->Type = Shdr.sh_type;
+ Sec->Flags = Shdr.sh_flags;
+ Sec->Addr = Shdr.sh_addr;
+ Sec->Offset = Shdr.sh_offset;
+ Sec->OriginalOffset = Shdr.sh_offset;
+ Sec->Size = Shdr.sh_size;
+ Sec->Link = Shdr.sh_link;
+ Sec->Info = Shdr.sh_info;
+ Sec->Align = Shdr.sh_addralign;
+ Sec->EntrySize = Shdr.sh_entsize;
+ Sec->Index = Index++;
+ Sections.push_back(std::move(Sec));
+ }
+}
+
+template <class ELFT> size_t Object<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.
+ return SHOffset + Sections.size() * sizeof(Elf_Shdr) + sizeof(Elf_Shdr);
+}
+
+template <class ELFT> Object<ELFT>::Object(const ELFObjectFile<ELFT> &Obj) {
+ const auto &ElfFile = *Obj.getELFFile();
+ const auto &Ehdr = *ElfFile.getHeader();
+
+ std::copy(Ehdr.e_ident, Ehdr.e_ident + 16, Ident);
+ Type = Ehdr.e_type;
+ Machine = Ehdr.e_machine;
+ Version = Ehdr.e_version;
+ Entry = Ehdr.e_entry;
+ Flags = Ehdr.e_flags;
+
+ readSectionHeaders(ElfFile);
+ readProgramHeaders(ElfFile);
+
+ SectionNames =
+ dyn_cast<StringTableSection>(Sections[Ehdr.e_shstrndx - 1].get());
+}
+
+template <class ELFT> void Object<ELFT>::sortSections() {
+ // Put all sections in offset order. Maintain the ordering as closely as
+ // possible while meeting that demand however.
+ auto CompareSections = [](const SecPtr &A, const SecPtr &B) {
+ return A->OriginalOffset < B->OriginalOffset;
+ };
+ std::stable_sort(std::begin(Sections), std::end(Sections), CompareSections);
+}
+
+template <class ELFT> void Object<ELFT>::assignOffsets() {
+ // Decide file offsets and indexes.
+ size_t PhdrSize = Segments.size() * sizeof(Elf_Phdr);
+ // We can put section data after the ELF header and the program headers.
+ uint64_t Offset = sizeof(Elf_Ehdr) + PhdrSize;
+ uint64_t Index = 1;
+ for (auto &Section : Sections) {
+ // The segment can have a different alignment than the section. In the case
+ // that there is a parent segment then as long as we satisfy the alignment
+ // of the segment it should follow that that the section is aligned.
+ if (Section->ParentSegment) {
+ auto FirstInSeg = Section->ParentSegment->firstSection();
+ if (FirstInSeg == Section.get()) {
+ Offset = alignTo(Offset, Section->ParentSegment->Align);
+ // There can be gaps at the start of a segment before the first section.
+ // So first we assign the alignment of the segment and then assign the
+ // location of the section from there
+ Section->Offset =
+ Offset + Section->OriginalOffset - Section->ParentSegment->Offset;
+ }
+ // We should respect interstitial gaps of allocated sections. We *must*
+ // maintain the memory image so that addresses are preserved. As, with the
+ // exception of SHT_NOBITS sections at the end of segments, the memory
+ // image is a copy of the file image, we preserve the file image as well.
+ // There's a strange case where a thread local SHT_NOBITS can cause the
+ // memory image and file image to not be the same. This occurs, on some
+ // systems, when a thread local SHT_NOBITS is between two SHT_PROGBITS
+ // and the thread local SHT_NOBITS section is at the end of a TLS segment.
+ // In this case to faithfully copy the segment file image we must use
+ // relative offsets. In any other case this would be the same as using the
+ // relative addresses so this should maintian the memory image as desired.
+ Offset = FirstInSeg->Offset + Section->OriginalOffset -
+ FirstInSeg->OriginalOffset;
+ }
+ // Alignment should have already been handled by the above if statement if
+ // this if this section is in a segment. Technically this shouldn't do
+ // anything bad if the alignments of the sections are all correct and the
+ // file image isn't corrupted. Still in sticking with the motto "maintain
+ // the file image" we should avoid messing up the file image if the
+ // alignment disagrees with the file image.
+ if (!Section->ParentSegment && Section->Align)
+ Offset = alignTo(Offset, Section->Align);
+ Section->Offset = Offset;
+ Section->Index = Index++;
+ if (Section->Type != SHT_NOBITS)
+ Offset += Section->Size;
+ }
+ // 'offset' should now be just after all the section data so we should set the
+ // section header table offset to be exactly here. This spot might not be
+ // aligned properly however so we should align it as needed. For 32-bit ELF
+ // this needs to be 4-byte aligned and on 64-bit it needs to be 8-byte aligned
+ // so the size of ELFT::Addr is used to ensure this.
+ Offset = alignTo(Offset, sizeof(typename ELFT::Addr));
+ SHOffset = Offset;
+}
+
+template <class ELFT> void Object<ELFT>::finalize() {
+ for (auto &Section : Sections)
+ SectionNames->addString(Section->Name);
+
+ sortSections();
+ assignOffsets();
+
+ // Finalize SectionNames first so that we can assign name indexes.
+ SectionNames->finalize();
+ // Finally now that all offsets and indexes have been set we can finalize any
+ // remaining issues.
+ uint64_t Offset = SHOffset + sizeof(Elf_Shdr);
+ for (auto &Section : Sections) {
+ Section->HeaderOffset = Offset;
+ Offset += sizeof(Elf_Shdr);
+ Section->NameIndex = SectionNames->findIndex(Section->Name);
+ Section->finalize();
+ }
+
+ for (auto &Segment : Segments)
+ Segment->finalize();
+}
+
+template <class ELFT>
+void Object<ELFT>::writeHeader(FileOutputBuffer &Out) const {
+ uint8_t *Buf = Out.getBufferStart();
+ Elf_Ehdr &Ehdr = *reinterpret_cast<Elf_Ehdr *>(Buf);
+ std::copy(Ident, Ident + 16, Ehdr.e_ident);
+ Ehdr.e_type = Type;
+ Ehdr.e_machine = Machine;
+ 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;
+}
+
+template <class ELFT>
+void Object<ELFT>::writeProgramHeaders(FileOutputBuffer &Out) const {
+ for (auto &Phdr : Segments)
+ Phdr->template writeHeader<ELFT>(Out);
+}
+
+template <class ELFT>
+void Object<ELFT>::writeSectionHeaders(FileOutputBuffer &Out) const {
+ uint8_t *Buf = Out.getBufferStart() + SHOffset;
+ // This reference serves to write the dummy section header at the begining
+ // of the file.
+ Elf_Shdr &Shdr = *reinterpret_cast<Elf_Shdr *>(Buf);
+ Shdr.sh_name = 0;
+ Shdr.sh_type = SHT_NULL;
+ Shdr.sh_flags = 0;
+ Shdr.sh_addr = 0;
+ Shdr.sh_offset = 0;
+ Shdr.sh_size = 0;
+ Shdr.sh_link = 0;
+ Shdr.sh_info = 0;
+ Shdr.sh_addralign = 0;
+ Shdr.sh_entsize = 0;
+
+ for (auto &Section : Sections)
+ Section->template writeHeader<ELFT>(Out);
+}
+
+template <class ELFT>
+void Object<ELFT>::writeSectionData(FileOutputBuffer &Out) const {
+ for (auto &Section : Sections)
+ Section->writeSection(Out);
+}
+
+template <class ELFT> void Object<ELFT>::write(FileOutputBuffer &Out) {
+ writeHeader(Out);
+ writeProgramHeaders(Out);
+ writeSectionData(Out);
+ writeSectionHeaders(Out);
+}
+
+template class Object<ELF64LE>;
+template class Object<ELF64BE>;
+template class Object<ELF32LE>;
+template class Object<ELF32BE>;