diff options
Diffstat (limited to 'compiler/elf_builder.h')
| -rw-r--r-- | compiler/elf_builder.h | 75 |
1 files changed, 56 insertions, 19 deletions
diff --git a/compiler/elf_builder.h b/compiler/elf_builder.h index 3d24d19919..bc7c83ed7d 100644 --- a/compiler/elf_builder.h +++ b/compiler/elf_builder.h @@ -110,18 +110,27 @@ class ElfBuilder FINAL { CHECK(sections.empty() || sections.back()->finished_); // The first ELF section index is 1. Index 0 is reserved for NULL. section_index_ = sections.size() + 1; - // Push this section on the list of written sections. - sections.push_back(this); + // Page-align if we switch between allocated and non-allocated sections, + // or if we change the type of allocation (e.g. executable vs non-executable). + if (!sections.empty()) { + if (header_.sh_flags != sections.back()->header_.sh_flags) { + header_.sh_addralign = kPageSize; + } + } // Align file position. if (header_.sh_type != SHT_NOBITS) { - header_.sh_offset = RoundUp(owner_->stream_.Seek(0, kSeekCurrent), header_.sh_addralign); - owner_->stream_.Seek(header_.sh_offset, kSeekSet); + header_.sh_offset = owner_->AlignFileOffset(header_.sh_addralign); + } else { + header_.sh_offset = 0; } // Align virtual memory address. if ((header_.sh_flags & SHF_ALLOC) != 0) { - header_.sh_addr = RoundUp(owner_->virtual_address_, header_.sh_addralign); - owner_->virtual_address_ = header_.sh_addr; + header_.sh_addr = owner_->AlignVirtualAddress(header_.sh_addralign); + } else { + header_.sh_addr = 0; } + // Push this section on the list of written sections. + sections.push_back(this); } // Finish writing of this section. @@ -170,8 +179,8 @@ class ElfBuilder FINAL { // and it will be zero-initialized when the ELF file is loaded in the running program. void WriteNoBitsSection(Elf_Word size) { DCHECK_NE(header_.sh_flags & SHF_ALLOC, 0u); - Start(); header_.sh_type = SHT_NOBITS; + Start(); header_.sh_size = size; End(); } @@ -293,12 +302,13 @@ class ElfBuilder FINAL { dynamic_(this, ".dynamic", SHT_DYNAMIC, SHF_ALLOC, &dynstr_, 0, kPageSize, sizeof(Elf_Dyn)), eh_frame_(this, ".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), eh_frame_hdr_(this, ".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0), - strtab_(this, ".strtab", 0, kPageSize), + strtab_(this, ".strtab", 0, 1), symtab_(this, ".symtab", SHT_SYMTAB, 0, &strtab_), debug_frame_(this, ".debug_frame", SHT_PROGBITS, 0, nullptr, 0, sizeof(Elf_Addr), 0), debug_info_(this, ".debug_info", SHT_PROGBITS, 0, nullptr, 0, 1, 0), debug_line_(this, ".debug_line", SHT_PROGBITS, 0, nullptr, 0, 1, 0), shstrtab_(this, ".shstrtab", 0, 1), + started_(false), virtual_address_(0) { text_.phdr_flags_ = PF_R | PF_X; bss_.phdr_flags_ = PF_R | PF_W; @@ -357,16 +367,25 @@ class ElfBuilder FINAL { virtual_address_ = address; } - void Start() { - // Reserve space for ELF header and program headers. - // We do not know the number of headers until later, so - // it is easiest to just reserve a fixed amount of space. - int size = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * kMaxProgramHeaders; + // Reserve space for ELF header and program headers. + // We do not know the number of headers until later, so + // it is easiest to just reserve a fixed amount of space. + // Program headers are required for loading by the linker. + // It is possible to omit them for ELF files used for debugging. + void Start(bool write_program_headers = true) { + int size = sizeof(Elf_Ehdr); + if (write_program_headers) { + size += sizeof(Elf_Phdr) * kMaxProgramHeaders; + } stream_.Seek(size, kSeekSet); + started_ = true; virtual_address_ += size; + write_program_headers_ = write_program_headers; } void End() { + DCHECK(started_); + // Write section names and finish the section headers. shstrtab_.Start(); shstrtab_.Write(""); @@ -386,8 +405,7 @@ class ElfBuilder FINAL { shdrs.push_back(section->header_); } Elf_Off section_headers_offset; - section_headers_offset = RoundUp(stream_.Seek(0, kSeekCurrent), sizeof(Elf_Off)); - stream_.Seek(section_headers_offset, kSeekSet); + section_headers_offset = AlignFileOffset(sizeof(Elf_Off)); stream_.WriteFully(shdrs.data(), shdrs.size() * sizeof(shdrs[0])); // Flush everything else before writing the program headers. This should prevent @@ -395,14 +413,21 @@ class ElfBuilder FINAL { // and partially written data if we suddenly lose power, for example. stream_.Flush(); - // Write the initial file headers. - std::vector<Elf_Phdr> phdrs = MakeProgramHeaders(); + // The main ELF header. Elf_Ehdr elf_header = MakeElfHeader(isa_); - elf_header.e_phoff = sizeof(Elf_Ehdr); elf_header.e_shoff = section_headers_offset; - elf_header.e_phnum = phdrs.size(); elf_header.e_shnum = shdrs.size(); elf_header.e_shstrndx = shstrtab_.GetSectionIndex(); + + // Program headers (i.e. mmap instructions). + std::vector<Elf_Phdr> phdrs; + if (write_program_headers_) { + phdrs = MakeProgramHeaders(); + CHECK_LE(phdrs.size(), kMaxProgramHeaders); + elf_header.e_phoff = sizeof(Elf_Ehdr); + elf_header.e_phnum = phdrs.size(); + } + stream_.Seek(0, kSeekSet); stream_.WriteFully(&elf_header, sizeof(elf_header)); stream_.WriteFully(phdrs.data(), phdrs.size() * sizeof(phdrs[0])); @@ -492,6 +517,14 @@ class ElfBuilder FINAL { return &stream_; } + off_t AlignFileOffset(size_t alignment) { + return stream_.Seek(RoundUp(stream_.Seek(0, kSeekCurrent), alignment), kSeekSet); + } + + Elf_Addr AlignVirtualAddress(size_t alignment) { + return virtual_address_ = RoundUp(virtual_address_, alignment); + } + private: static Elf_Ehdr MakeElfHeader(InstructionSet isa) { Elf_Ehdr elf_header = Elf_Ehdr(); @@ -666,9 +699,13 @@ class ElfBuilder FINAL { // List of used section in the order in which they were written. std::vector<Section*> sections_; + bool started_; + // Used for allocation of virtual address space. Elf_Addr virtual_address_; + size_t write_program_headers_; + DISALLOW_COPY_AND_ASSIGN(ElfBuilder); }; |